Campbell Biology

return to the atmosphere as gases, while others are carried ▼ Fungi decomposing
out of the ecosystem by moving water or by wind. Like a dead tree
organisms, ecosystems are open systems, absorbing energy
and mass and releasing heat and waste products. ▲ Rod-shaped and spherical bacteria
in compost (colorized SEM)
Most gains and losses to ecosystems are small compared
to the amounts that cycle within them. Even so, the balance Figure 55.3  Detritivores.
between inputs and outputs is important because it determines
whether an ecosystem stores or loses a given element. In partic- Another group of heterotrophs is the detritivores, or
ular, if a nutrient’s outputs exceed its inputs, that nutrient will decomposers, terms used synonymously in this text to refer
eventually limit production in that ecosystem. Human activi- to consumers that get their energy from detritus. Detritus
ties often change the balance of inputs and outputs consider- is nonliving organic material, such as the remains of dead
ably, as we’ll see later in this chapter and in Concept 56.4. organisms, feces, fallen leaves, and wood. Although some
animals (such as earthworms) feed on detritus, the main
Energy, Mass, and Trophic Levels detritivores are prokaryotes and fungi (Figure 55.3). These
organisms secrete enzymes that digest organic material; they
Ecologists group species in an ecosystem into trophic levels then absorb the breakdown products. Many detritivores are
based on feeding relationships (see Concept 54.2). The trophic in turn eaten by secondary and tertiary consumers. In a for-
level that ultimately supports all others consists of autotrophs, est, for instance, birds eat earthworms that have been feeding
also called the primary producers of the ecosystem. Most on leaf litter and its associated prokaryotes and fungi. As a
autotrophs are photosynthetic organisms that use light energy result, chemicals originally synthesized by plants pass from
to synthesize sugars and other organic compounds, which the plants to leaf litter to detritivores to birds.
they use as fuel for cellular respiration and as building material
for growth. The most common autotrophs are plants, algae, By recycling chemical elements to producers, detritivores
and photosynthetic prokaryotes, although chemosynthetic also play a key role in the trophic relationships of an ecosys-
prokaryotes are the primary producers in ecosystems such as tem (Figure 55.4). Detritivores convert organic matter from
deep-sea hydrothermal vents (see Figure 52.15) and places all trophic levels to inorganic compounds usable by primary
deep under the ground or ice.

Organisms in trophic levels above the primary producers
are heterotrophs, which depend directly or indirectly on
the outputs of primary producers for their source of energy.
Herbivores, which eat plants and other primary producers,
are primary consumers. Carnivores that eat herbivores
are secondary consumers, and carnivores that eat other
carnivores are tertiary consumers.

Figure 55.4  An overview of energy and Loss of heat Sun Key
nutrient dynamics in an ecosystem. Energy Primary producers
enters, flows through, and exits an ecosystem, Chemical cycling
whereas chemical nutrients cycle within it. Energy Energy flow
(dark orange arrows) entering from the sun as
radiation is transferred as chemical energy through Primary consumers Detritus
the food web; each of these units of energy Microorganisms
ultimately exits as heat radiated into space. Most Secondary and
transfers of nutrients (blue arrows) through the tertiary consumers and other
food web lead eventually to detritus; the nutrients detritivores
then cycle back to the primary producers.

VISUAL SKILLS In this diagram, one blue arrow
leads to the box labeled “Primary consumers,” and three
blue arrows come out of this box. For each of these four
arrows, describe an example of nutrient transfer that the
arrow could represent.

1238 unit eight  Ecology

producers. When the detritivores excrete waste products About 50% of incoming solar radiation is absorbed, scattered,
or die, those inorganic compounds are returned to the soil. or reflected by clouds and dust in the atmosphere. The amount
Producers can then absorb these elements and use them to of solar radiation that ultimately reaches Earth’s surface limits
synthesize organic compounds. If decomposition stopped, the possible photosynthetic output of ecosystems.
life as we know it would cease as detritus piled up and the
supply of ingredients needed to synthesize organic matter However, only a small fraction of the sunlight that reaches
was exhausted. Earth’s surface is actually used in photosynthesis. Much of
the radiation strikes materials that don’t photosynthesize,
Animation: Energy Flow and Chemical Cycling such as ice and soil. Of the radiation that does reach photo-
synthetic organisms, only certain wavelengths are absorbed
Concept Check 55.1 by photosynthetic pigments (see Figure 10.9); the rest is
transmitted, reflected, or lost as heat. As a result, only about
1. Why is the transfer of energy in an ecosystem referred to 1% of the visible light that strikes photosynthetic organisms
as energy flow, not energy cycling? is converted to chemical energy. Nevertheless, Earth’s
primary producers create about 150 billion metric tons
2. WHAT IF? You are studying nitrogen cycling on the (1.50 * 1014 kg) of organic material each year.
Serengeti Plain in Africa. During your experiment, a herd
of migrating wildebeests grazes through your study plot. Gross and Net Production
What would you need to know to measure their effect
on nitrogen balance in the plot? Total primary production in an ecosystem is known as that
ecosystem’s gross primary production (GPP)—the
3. MAKE CONNECTIONS Use the second law of thermody- amount of energy from light (or chemicals, in chemoau-
namics to explain why an ecosystem’s energy supply must totrophic systems) converted to the chemical energy of
be continually replenished (see Concept 8.1). organic molecules per unit time. Not all of this production is
For suggested answers, see Appendix A. stored as organic material in the primary producers because
they use some of the molecules as fuel for their own cellular
Concept  55.2 respiration. Net primary production (NPP) is equal
to gross primary production minus the energy used by the
Energy and other limiting factors primary producers (autotrophs) for their cellular respiration
control primary production in (Ra, where “a” stands for autotrophs):
ecosystems
NPP = GPP - Ra
The theme of energy transfer underlies all biological inter-
actions (see Concept 1.1). In most ecosystems, the amount On average, NPP is about one-half of GPP. To ecologists, NPP
of light energy converted to chemical energy—in the form is the key measurement because it represents the storage of
of organic compounds—by autotrophs during a given chemical energy that will be available to consumers in the
time period is the ecosystem’s primary production. In ecosystem. Using the analogy of a paycheck, you can think of
ecosystems where the primary producers are chemoauto- net primary production (NPP) as the take-home pay, which
trophs, the initial energy input is chemical, and the initial equals gross primary production (GPP), the gross pay, minus
products are the organic compounds synthesized by the respiration (Ra), the taxes.
microorganisms.
Net primary production can be expressed as energy per
Ecosystem Energy Budgets unit area per unit time [ J/(m2 · yr)] or as biomass (mass of
vegetation) added per unit area per unit time [g/(m2 · yr)].
In most ecosystems, primary producers use light energy to (Note that biomass is usually expressed in terms of the dry
synthesize energy-rich organic molecules, and consumers mass of organic material.) An ecosystem’s NPP should not
acquire their organic fuels secondhand (or even third- or be confused with the total biomass of photosynthetic auto-
fourth-hand) through food webs (see Figure 54.15). Therefore, trophs present. The net primary production is the amount of
the total amount of photosynthetic production sets the new biomass added in a given period of time. Although the
“spending limit” for the entire ecosystem’s energy budget. total biomass of a forest is large, its NPP may actually be less
than that of some grasslands; grasslands do not accumulate
The Global Energy Budget as much biomass as forests because animals consume the
plants rapidly and because grasses and herbs decompose
Each day, Earth’s atmosphere is bombarded by approximately more quickly than trees do.
1022 joules of solar radiation (1 J = 0.239 cal). This is enough
energy to supply the demands of the entire human population Satellites provide a powerful tool for studying global pat-
for 19 years at 2013 energy consumption levels. The intensity terns of primary production. Images produced from satellite
of the solar energy striking Earth varies with latitude, with data show that different ecosystems vary considerably in
the tropics receiving the greatest input (see Figure 52.3).

chapter 55  Ecosystems and Restoration Ecology 1239

Figure 55.5  Global net Net primary production
primary production. The map [kg carbon/(m2• yr)]
is based on satellite-collected
data, such as amount of sunlight 3
absorbed by vegetation. Note that
tropical land areas have the highest 2
rates of production (yellow and red
on the map). 1

VISUAL SKILLS Does this map
accurately reflect the significance of
wetlands, coral reefs, and coastal
zones, which are highly productive
habitats? Explain.

0

their NPP (Figure 55.5). For example, tropical rain forests are Light Limitation
among the most productive terrestrial ecosystems and con-
tribute a large portion of the planet’s NPP. Estuaries and coral Because solar radiation drives photosynthesis, you would
reefs also have very high NPP, but their contribution to the expect light to be a key variable in controlling primary pro-
global total is smaller because these ecosystems cover only duction in oceans. Indeed, the depth of light penetration
about one-tenth the area covered by tropical rain forests. In affects primary production throughout the photic zone of
contrast, while the open oceans are relatively unproductive, an ocean or lake (see Figure 52.13). About half of the solar
their vast size means that together they contribute as much radiation is absorbed in the first 15 m of water. Even in “clear”
global NPP as terrestrial systems do. water, only 5–10% of the radiation may reach a depth of 75 m.

Whereas NPP can be expressed as the amount of new biomass If light were the main variable limiting primary produc-
added by producers in a given period of time, net ecosystem tion in the ocean, you would expect production to increase
production (NEP) is a measure of the total biomass accumula- along a gradient from the poles toward the equator, which
tion during that time. NEP is defined as gross primary produc- receives the greatest intensity of light. However, you can see
tion minus the total respiration of all organisms in the system in Figure 55.5 that there is no such gradient. What other factor
(RT)—not just primary producers, as for the calculation of NPP, strongly influences primary production in the ocean?
but decomposers and other heterotrophs as well:
Nutrient Limitation
NEP = GPP - RT
More than light, nutrients limit primary production in most
NEP is useful to ecologists because its value determines whether oceans and lakes. A limiting nutrient is the element that
an ecosystem is gaining or losing carbon over time. A forest may must be added for production to increase. The nutrients that
have a positive NPP but still lose carbon if heterotrophs release most often limit marine production are nitrogen and phos-
it as CO2 more quickly than primary producers incorporate it phorus. Concentrations of these nutrients are typically low in
into organic compounds. the photic zone because they are rapidly taken up by phyto-
plankton and because detritus tends to sink.
The most common way to estimate NEP is to measure the
net flux (flow) of CO2 or O2 entering or leaving the ecosystem. In one study, detailed in Figure 55.6, nutrient enrichment
If more CO2 enters than leaves, the system is storing carbon. experiments found that nitrogen was limiting phytoplank-
Because O2 release is directly coupled to photosynthesis and ton growth off the south shore of Long Island, New York.
respiration (see Figure 9.2), a system that is giving off O2 is also One practical application of this work is in preventing algal
storing carbon. On land, ecologists typically measure only blooms caused by excess nitrogen runoff that fertilizes the
the net flux of CO2 from ecosystems because detecting small phytoplankton. Preventing such blooms is critical because
changes in O2 flux in a large atmospheric O2 pool is difficult. their occurrence can lead to the formation of large marine
“dead zones,” regions in which oxygen concentrations drop
Next, we’ll examine factors that limit production in eco- to levels that are fatal to many organisms (see Figure 56.24).
systems, focusing first on aquatic ecosystems.
The macronutrients nitrogen and phosphorus are not the
Primary Production in Aquatic Ecosystems only nutrients that limit aquatic production. Several large
areas of the ocean have low phytoplankton densities despite
In aquatic (marine and freshwater) ecosystems, both light and relatively high nitrogen concentrations. The Sargasso Sea,
nutrients are important in controlling primary production. a subtropical region of the Atlantic Ocean, has some of the

1240 unit eight  Ecology

Figure 55.6 Table 55.1  Nutrient Enrichment Experiment for Sargasso
Sea Samples 
Inquiry  Which nutrient limits phytoplankton
production along the coast of Long Island? Nutrients Added to Experimental Relative Uptake
Culture of 14C by Cultures*
Experiment  Pollution from duck farms concentrated near
Moriches Bay adds both nitrogen and phosphorus to the coastal None (controls)  1.00
water off Long Island, New York. To determine which nutrient
limits phytoplankton growth in this area, John Ryther and William Nitrogen (N) + phosphorus (P) only  1.10
Dunstan, of the Woods Hole Oceanographic Institution, cultured the N + P + metals, excluding iron (Fe)  1.08
phytoplankton Nannochloris atomus with water collected from sev- N + P + metals, including Fe 12.90
eral sites, identified as A through G. They added either ammonium N + P + Fe 12.00
(NH4+) or phosphate (PO43-) to some of the cultures.
Results  The addition of ammonium caused heavy phytoplankton *14C uptake by cultures measures primary production.
growth in the cultures, but the addition of phosphate did not.
Data from  D. W. Menzel and J. H. Ryther, Nutrients limiting the production
30 Ammonium of phytoplankton in the Sargasso Sea, with special reference to iron, Deep Sea
enriched Research 7:276–281 (1961).

Phytoplankton density 24 Phosphate INTERPRET THE DATA The element molybdenum (Mo) is another
(millions of cells per mL) enriched micronutrient that can limit primary production in the oceans. If the researchers

found the following results for additions of Mo, what would you conclude

about its relative importance for growth?

Unenriched N + P + Mo 6.0
18 control
N + P + Fe + Mo 72.0

12 occur in the Southern Ocean (also called the Antarctic
Ocean), along the equator, and in the coastal waters off Peru,
6 California, and parts of western Africa.

0 Nutrient limitation is also common in freshwater lakes.
ABCDE FG During the 1970s, scientists showed that the sewage and fertil-
Collection site izer runoff from farms and lawns adds considerable nutrients
to lakes, promoting the growth of primary producers. When
Conclusion  The researchers concluded that nitrogen is the nutrient the primary producers die, detritivores decompose them,
that limits phytoplankton growth in this ecosystem because adding depleting the water of much or all of its oxygen. The ecologi-
phosphorus did not increase Nannochloris growth, whereas adding cal impacts of this process, known as eutrophication (from
nitrogen increased phytoplankton density dramatically. the Greek eutrophos, well nourished), include the loss of many
fish species from the lakes (see Figure 52.15).
Data from  J. H. Ryther and W. M. Dunstan, Nitrogen, phosphorus, and eutrophication
in the coastal marine environment, Science 171:1008 –1013 (1971). To control eutrophication, scientists need to know which
nutrient is responsible. While nitrogen rarely limits primary
WHAT IF? Predict how the results would change if water samples were production in lakes, many whole-lake experiments showed
drawn from areas where new duck farms had greatly increased the amount that phosphorus availability limited cyanobacterial growth.
of pollution in the water. Explain. This and other ecological research led to the use of phosphate-
free detergents and other water quality reforms.
clearest water in the world because of its low phytoplankton
density. Nutrient enrichment experiments have revealed that Primary Production in Terrestrial Ecosystems
the availability of the micronutrient iron limits primary pro-
duction there (Table 55.1). Windblown dust from land sup- At regional and global scales, temperature and moisture are
plies most of the iron to the oceans but is relatively scarce in the the main factors controlling primary production in terres-
Sargasso Sea and certain other regions compared to the oceans trial ecosystems. Tropical rain forests, with their warm, wet
as a whole. conditions that promote plant growth, are the most produc-
tive terrestrial ecosystems (see Figure 55.5). In contrast, low-
On the flip side, areas of upwelling, where deep, nutrient- productivity systems are generally hot and dry, like many
rich waters circulate to the ocean surface, have exceptionally deserts, or cold and dry, like arctic tundra. Between these
high primary production. This fact supports the hypothesis extremes lie the temperate forest and grassland ecosystems,
that nutrient availability determines marine primary pro- with moderate climates and intermediate productivity.
duction. Because upwelling stimulates growth of the phyto-
plankton that form the base of marine food webs, upwelling The climate variables of precipitation and temperature
areas typically host highly productive, diverse ecosystems are very useful for predicting NPP in terrestrial ecosystems.
and are prime fishing locations. The largest areas of upwelling For example, primary production is greater in wetter ecosys-
tems, as shown for the plot of NPP and annual precipitation

chapter 55  Ecosystems and Restoration Ecology 1241

Figure 55.7  A global relationship between net primaryNet annual primary productionthat climate change could affect production in terres-
production and mean annual precipitation for terrestrial[above ground, dry g/(m2 • yr)]trial ecosystems—and it does. For example, satellite data
ecosystems. showed that from 1982 to 1999, NPP increased by 6% in
terrestrial ecosystems. Nearly half of this increase occurred
1,400 in the tropical forests of the Amazon, where changing cli-
mate patterns had caused cloud cover to decrease, thereby
1,200 increasing the amount of solar energy available to primary
producers. Since 2000, however, these gains in NPP have
1,000 been erased. This reversal was affected by another aspect of
climate change: a series of major droughts in the southern
800 hemisphere.

600 Another effect of climate change on NPP can be seen
in the impact of “hotter droughts” on wildfires and insect
400 outbreaks. Consider forests in the American southwest. In
recent decades, the forests of this region have experienced
200 droughts driven by climate warming and changing patterns
of precipitation. These ongoing droughts, in turn, have led to
0 20 40 60 80 100 120 140 160 180 200 increases in the area burned by wildfires and the area affected
Mean annual precipitation (cm) by outbreaks of bark beetles such as the mountain pine beetle
Dendroctonus ponderosae (Figure 55.8). As a result, tree mortal-
in Figure 55.7. NPP also increases with temperature and the ity has increased and NPP has decreased in these forests.
amount of solar energy available to drive evaporation and
transpiration. Figure 55.8  Climate change, wildfires, and insect
outbreaks. Forests in the American southwest are experiencing
Nutrient Limitations and Adaptations hotter droughts caused by rising temperatures in the summer and
That Reduce Them reduced snowfall in the winter. The drought-stress index indicates
how greatly trees are stressed by these conditions; rising values
Evolution Soil nutrients can also limit primary production of this index correspond to increasing drought. Higher drought
in terrestrial ecosystems. As in aquatic systems, nitrogen and stress correlates with increasing
phosphorus are the nutrients that most commonly limit ter- area burned by wildfires (top) and
restrial production. Globally, nitrogen limits plant growth affected by bark beetles (bottom),
most. Phosphorus limitations are common in older soils where which specifically target drought-
phosphate molecules have been leached away by water, such as stressed trees with weakened
in many tropical ecosystems. Note that adding a nonlimiting defenses.
nutrient, even one that is scarce, will not stimulate production.
Conversely, adding more of the limiting nutrient will increase Area burned by wildfires 104 2 Drought-stress index:
production until some other nutrient becomes limiting. (km2, log scale): 103
102 0
Various adaptations have evolved in plants that can 10
increase their uptake of limiting nutrients. One i­mportant –2
adaptation is the mutualism between plant roots and 1
­nitrogen-fixing bacteria. Another is the mycorrhizal associa- Area affected by 1 Drought-stress index:
tion between plant roots and fungi that supply phosphorus bark beetles 104 0
and other limiting elements to plants (see Figure 37.15). 103 –1
Plant roots also have hairs and other anatomical features that (km2, log scale): 102 2014
increase the area of soil in contact with the roots (see Figures
33.9 and 35.3). Many plants release enzymes and other sub- 1997 2000 2005 2010
stances into the soil that increase the availability of limiting Year
nutrients; such substances include phosphatases, which
cleave a phosphate group from larger molecules, and certain
molecules (called chelating agents) that make micronutrients
such as iron more soluble in the soil.

Effects of Climate Change on Production

As we’ve seen, climatic factors such as temperature and
precipitation affect terrestrial NPP. Thus, we might expect

1242 unit eight  Ecology

Problem-Solving Exercise

Can an insect In this exercise, you will test whether an outbreak of the mountain pine beetle (Dendroctonus
outbreak threaten ponderosae) alters the amount of CO2 that a forest ecosystem absorbs from and releases to
a forest’s ability the atmosphere.
to absorb CO2 from
the atmosphere? Your Approach The principle guiding your investigation is that every ecosystem both ab-
sorbs and releases CO2. Net ecosystem production (NEP) indicates whether
One way to combat climate change is an ecosystem is a carbon sink (absorbing more CO2 from the atmosphere
to plant trees, since trees absorb large than it releases; this occurs when NEP 7 0) or a carbon source (releasing
amounts of CO2 from the atmosphere, more CO2 than it absorbs; NEP 6 0). To find out if the mountain pine bee-
converting it to biomass through photo- tle affects NEP, you will determine a forest’s NEP before and after a recent
synthesis. But what happens to the car- outbreak of this insect.
bon stored as biomass in trees when an
insect population explodes in number? Your Data From 2000 to 2006, an outbreak of the mountain pine beetle killed millions
Such insect outbreaks have become more of trees in British Columbia, Canada. The impact of such outbreaks on
frequent with climate change. whether forests gain carbon (NEP 7 0) or lose carbon (NEP 6 0) was poorly
understood. To find out, ecologists estimated net primary production
(NPP) and cellular respiration by decomposers and other heterotrophs (Rh),
before and after the outbreak. These data allow forest NEP to be calculated
from the equation NEP = NPP - Rh.

Before outbreak #NPP #Rh
After outbreak
[g/(m2 yr)] [g/(m2 yr)]
440 408
400 424

Your Analysis 1. Before the outbreak, was the forest a carbon sink or a carbon source?
After the outbreak?
A tree with dozens of “pitch tubes,”
indications of a damaging outbreak of 2. NEP is often defined as NEP = GPP - RT, where GPP is gross primary
mountain pine beetles (inset) production and RT equals cellular respiration by autotrophs (Ra)
plus cellular respiration by heterotrophs (Rh). Use the relation
Instructors: A version of this NPP = GPP - Ra to show that the two equations for NEP introduced
Problem-Solving Exercise can be in this exercise are equivalent.
assigned in MasteringBiology.
3. Based on your results in question 1, predict whether the mountain
pine beetle outbreak could have feedback effects on the global
climate. Explain.

Climate change can also affect whether an ecosystem change by releasing more CO2 than it absorbs. In the
stores or loses carbon over time. As discussed earlier, net eco- Problem-Solving Exercise, you can examine how out-
system production, or NEP, reflects the total biomass accu- breaks of an insect population may affect the NEP of
mulation that occurs during a given period of time. When ­forest ecosystems.
NEP 7 0, the ecosystem gains more carbon than it loses;
such ecosystems store carbon and are said to be a ­carbon Concept Check 55.2
sink. In contrast, when NEP 6 0, the ecosystem loses more
carbon than it gains; such ecosystems are a carbon source. 1. Why is only a small portion of the solar energy
that strikes Earth’s atmosphere stored by primary
Recent research shows that climate change can cause an producers?
ecosystem to switch from a carbon sink to a carbon source.
For example, in some arctic ecosystems, climate warming 2. How can ecologists experimentally determine the factor
has increased the metabolic activities of soil microorgan- that limits primary production in an ecosystem?
isms, causing an uptick in the amount of CO2 produced in
cellular respiration. In these ecosystems, the total amount 3. WHAT IF? Suppose a forest was heavily burned by a
of CO2 produced in cellular respiration now exceeds what is wildfire. Predict how NEP of this forest would change
absorbed in photosynthesis. As a result, these ecosystems— over time.
which once were carbon sinks—are now carbon sources.
When this happens, an ecosystem may contribute to climate 4. MAKE CONNECTIONS Explain how nitrogen and
­phosphorus, the nutrients that most often limit primary
production, are necessary for the Calvin cycle to function
in photosynthesis (see Concept 10.3).
For suggested answers, see Appendix A.

chapter 55  Ecosystems and Restoration Ecology 1243

Concept  55.3 We can measure the efficiency of animals as energy trans-
formers using the following equation:
Energy transfer between trophic
levels is typically only 10% efficient Production efficiency = Net secondary production * 100%
Assimilation of primary production
The amount of chemical energy in consumers’ food that is con-
verted to their own new biomass during a given period is called Net secondary production is the energy stored in biomass rep-
the secondary production of the ecosystem. Consider the resented by growth and reproduction. Assimilation consists
transfer of organic matter from primary producers to herbi- of the total amount of energy an organism has consumed and
vores, the primary consumers. In most ecosystems, herbivores used for growth, reproduction, and respiration. Production
eat only a small fraction of plant material produced; globally, efficiency, therefore, is the percentage of energy stored in
they consume only about one-sixth of total plant production. assimilated food that is used for growth and reproduction,
Moreover, they cannot digest all the plant material that they not respiration. For the caterpillar in Figure 55.9, production
do eat, as anyone who has walked through a field where cattle efficiency is 33%; 67 J of the 100 J of assimilated energy is used
have been grazing will attest. Most of an ecosystem’s produc- for respiration. (The 100 J of energy lost as undigested material
tion is eventually consumed by detritivores. Let’s analyze the in feces does not count toward assimilation.) Birds and mam-
process of energy transfer more closely. mals typically have low production efficiencies, in the range
of 1–3%, because they use so much energy in maintaining a
Production Efficiency constant, high body temperature. Fishes, which are mainly
ectothermic (see Concept 40.3), have production efficiencies
We’ll begin by examining secondary production in one around 10%. Insects and microorganisms are even more effi-
organism—a caterpillar. When a caterpillar feeds on a leaf, cient, with production efficiencies averaging 40% or more.
only about 33 J out of 200 J, or one-sixth of the potential
energy in the leaf, is used for secondary production, or growth Trophic Efficiency and Ecological Pyramids
(Figure 55.9). The caterpillar stores some of the remaining
energy in organic compounds that will be used for cellular res- Let’s scale up now from the production efficiencies of individ-
piration and passes the rest in its feces. The energy in the feces ual consumers to the flow of energy through trophic levels.
remains in the ecosystem temporarily, but most of it is lost as
heat after the feces are consumed by detritivores. The energy Trophic efficiency is the percentage of production
used for the caterpillar’s respiration is also eventually lost from transferred from one trophic level to the next. Trophic
the ecosystem as heat. Only the chemical energy stored by efficiencies must always be less than production efficien-
herbivores as biomass, through growth or the production of cies because they take into account not only the energy lost
offspring, is available as food to secondary consumers. through respiration and contained in feces, but also the
energy in organic material in a lower trophic level that is
Figure 55.9  Energy partitioning within a link of the not consumed by the next trophic level. Trophic efficiencies
food chain. range from roughly 5% to 20% in different ecosystems, but
on average are only about 10%. In other words, 90% of the
Plant material energy available at one trophic level typically is not trans-
eaten by caterpillar ferred to the next. This loss is multiplied over the length of
a food chain. If 10% of available energy is transferred from
200 J primary producers to primary consumers, such as caterpillars,
and 10% of that energy is transferred to secondary consumers
Feces 100 J 67 J Cellular (carnivores), then only 1% of net primary production is avail-
respiration able to secondary consumers (10% of 10%). In the Scientific
Skills Exercise, you can calculate trophic efficiency and
33 J other measures of energy flow in a salt marsh ecosystem.

Not assimilated Growth (new biomass; The progressive loss of energy along a food chain limits
secondary production) the abundance of top-level carnivores that an ecosystem can
Assimilated support. Only about 0.1% of the chemical energy fixed by
photosynthesis can flow all the way through a food web to a
INTERPRET THE DATA What percentage of the energy in the caterpillar’s tertiary consumer, such as a snake or a shark. This explains
food is actually used for secondary production (growth)? why most food webs include only about four or five trophic
levels (see Figure 54.15).

The loss of energy with each transfer in a food chain
can be represented by an energy pyramid, in which the net
productions of different trophic levels are arranged in tiers
(Figure 55.10). The width of each tier is proportional to the

1244 unit eight  Ecology

Scientific Skills Exercise Data from the Study

Interpreting Form of Energy kcal/(m2 ∙ yr)
Quantitative Data
Solar radiation 600,000
How Efficient Is Energy Gross grass production 34,580
Transfer in a Salt Marsh Net grass production 6,585
Ecosystem?  Gross insect production 305
In a classic experiment, John Net insect production 81
Teal studied the flow of energy Detritus leaving marsh 3,671
through the producers, consum-
ers, and detritivores in a salt Data from  J. M. Teal, Energy flow in the salt marsh ecosystem of Georgia, Ecology
marsh. In this exercise, you will use the data from this study to 43:614 – 624 (1962).
calculate some measures of energy transfer between trophic levels in
this ecosystem. Interpret the Data

How the Study Was Done  Teal measured the amount of solar 1. What percentage of the solar energy that reaches the marsh is incor-
radiation entering a salt marsh in Georgia over a year. He also porated into gross primary production? Into net primary production?
measured the aboveground biomass of the dominant primary pro-
ducers, which were grasses, as well as the biomass of the dominant 2. How much energy is lost by primary producers as respiration in this
consumers, including insects, spiders, and crabs, and of the detritus ecosystem? How much is lost as respiration by the insect population?
that flowed out of the marsh to the surrounding coastal waters. To
determine the amount of energy in each unit of biomass, he dried 3. If all of the detritus leaving the marsh is plant material, what per-
the biomass, burned it in a calorimeter, and measured the amount centage of all net primary production leaves the marsh as detritus
of heat produced. each year?

Instructors: A version of this Scientific Skills Exercise can be
assigned in MasteringBiology.

net production, expressed in joules, of each trophic level. are so inefficient (Figure 55.11a). Certain aquatic ecosys-
The highest level, which represents top-level predators, tems, however, have inverted biomass pyramids: Primary
contains relatively few individuals. The small population consumers outweigh the producers in these ecosystems
size typical of top predators is one reason they tend to be (Figure 55.11b). Such inverted biomass pyramids occur
vulnerable to extinction (and to the evolutionary conse- because the producers—phytoplankton—grow, reproduce,
quences of small population size; see Concept 23.3). and are consumed so quickly by the zooplankton that their
total biomass remains at comparatively low levels. However,
One important ecological consequence of low trophic because the phytoplankton continually replace their biomass
efficiencies is represented in a biomass pyramid, in which
each tier represents the total dry mass of all organisms in Figure 55.11  Pyramids of biomass. Numbers denote the dry
one trophic level. Most biomass pyramids narrow sharply mass of all organisms at each trophic level.
from primary producers at the base to top-level carnivores
at the apex because energy transfers between trophic levels

Figure 55.10  An idealized pyramid of energy. This example Trophic level Dry mass
assumes a trophic efficiency of 10% for each link in the food chain. (g/m2)
Notice that primary producers convert only about 1% of the energy Tertiary consumers
available to them to net primary production. Secondary consumers 1.5
11
Tertiary Primary consumers 37
consumers Primary producers 809

10 J (a) Most biomass pyramids show a sharp decrease in biomass at
successively higher trophic levels, as illustrated by data from a
Secondary 100 J Florida bog.
consumers

Primary Trophic level Dry mass
consumers (g/m2)
Primary 1,000 J
producers 10,000 J Primary consumers (zooplankton) 21
1,000,000 J of sunlight Primary producers (phytoplankton) 4

(b) In some aquatic ecosystems, such as the English Channel,
a small biomass of primary producers (phytoplankton) supports
a larger biomass of primary consumers (zooplankton).

chapter 55  Ecosystems and Restoration Ecology 1245

at such a rapid rate, they can support a biomass of zoo- Figure 55.12
plankton bigger than their own biomass. Likewise, because
phytoplankton reproduce so quickly and have much higher Inquiry  How does temperature affect litter
production than zooplankton, the pyramid of energy for this decomposition in an ecosystem?
ecosystem is still bottom-heavy, like the one in Figure 55.10.
Experiment  Researchers with the Canadian Forest Service placed
The dynamics of energy flow through ecosystems have identical samples of organic material—litter—on the ground in 21 sites
implications for human consumers. For example, eating across Canada. Three years later, they returned to see how much of
meat is a relatively inefficient way of tapping photosynthetic each sample had decomposed.
production. The same pound of soybeans that a person could Results  The mass of litter in the warmest ecosystem decreased four
eat for protein produces only a fifth of a pound of beef or less times faster than in the coldest ecosystem.
when fed to a cow. Agriculture worldwide could, in fact, feed
many more people and require less land if we all fed more Percent of mass lost 80 Ecosystem
efficiently—as primary consumers, eating plant material. 70 type
60
Concept Check 55.3 50 Subarctic
40 Boreal
1. If an insect that eats plant seeds containing 100 J of 30 Temperate
energy uses 30 J of that energy for respiration and 20 Grassland
excretes 50 J in its feces, what is the insect’s net second- 10 Mountain
ary production? What is its production efficiency?
0 –10 –5 0 5 10
2. Tobacco leaves contain nicotine, a poisonous compound –15
that is energetically expensive for the plant to make.
What advantage might the plant gain by using some of Mean annual temperature (°C)
its resources to produce nicotine?
Conclusion  Decomposition rate increases with temperature across
3. WHAT IF? Detritivores are consumers that obtain their much of Canada.
energy from detritus. How many joules of energy are
potentially available to detritivores in the ecosystem Data from  J. A. Trofymow and the CIDET Working Group, The Canadian Intersite
represented in Figure 55.10? Decomposition Experiment: Project and Site Establishment Report (Information Report
BC-X-378), Natural Resources Canada, Canadian Forest Service, Pacific Forestry Centre
For suggested answers, see Appendix A. (1998) and T. R. Moore et al., Litter decomposition rates in Canadian forests, Global
Change Biology 5:75–82 (1999).
Concept  55.4
WHAT IF? What factors other than temperature might also have varied
Biological and geochemical processes across these 21 sites? How might this variation have affected the interpretation
cycle nutrients and water in ecosystems of the results?

Although most ecosystems receive abundant solar energy, the higher temperatures and more abundant precipitation in
chemical elements are available only in limited amounts. Life tropical rain forests. Because decomposition in a tropical rain
therefore depends on the recycling of essential chemical ele- forest is rapid, relatively little organic material accumulates
ments. Much of an organism’s chemical stock is replaced con- as leaf litter on the forest floor; about 75% of the ecosystem’s
tinuously as nutrients are assimilated and waste products are nutrients is present in the woody trunks of trees, and only
released. When the organism dies, the atoms in its body are about 10% is contained in the soil. Thus, the relatively low
returned to the atmosphere, water, or soil by decomposers. concentrations of some nutrients in the soil of tropical rain
By liberating nutrients from organic matter, decomposition forests result from a short cycling time, not from a lack of
replenishes the pools of inorganic nutrients that plants and these elements in the ecosystem. In temperate forests, where
other autotrophs use to build new organic matter. decomposition is much slower, the soil may contain as much
as 50% of all the organic material in the ecosystem. The nutri-
Decomposition and Nutrient Cycling Rates ents that are present in temperate forest detritus and soil may
remain there for years before plants assimilate them.
Decomposers are heterotrophs that get their energy from
detritus. Their growth is controlled by the same factors that Decomposition on land is also slower when conditions
limit primary production in ecosystems, including tem- are either too dry for decomposers to thrive or too wet to sup-
perature, moisture, and nutrient availability. Decomposers ply them with enough oxygen. Ecosystems that are cold and
usually grow faster and decompose material more quickly in wet, such as peatlands, store large amounts of organic matter.
warmer ecosystems (Figure 55.12). In tropical rain forests, Decomposers grow poorly there, and net primary production
most organic material decomposes in a few months to a few greatly exceeds the rate of decomposition.
years, whereas in temperate forests, decomposition takes four
to six years, on average. The difference is largely the result of In aquatic ecosystems, decomposition in anaerobic muds
can take 50 years or longer. Bottom sediments are comparable
1246 unit eight  Ecology

to the detritus layer in terrestrial ecosystems, but algae and to the soil by decomposers. In aquatic systems, however, they
aquatic plants usually assimilate nutrients directly from the cycle more broadly as dissolved forms carried in currents.
water. Thus, the sediments often constitute a nutrient sink,
and aquatic ecosystems are very productive only when there Let’s first look at a general model of nutrient cycling that
is exchange between the bottom layers of water and surface includes reservoirs where elements exist and processes that
waters (as occurs in the upwelling regions described earlier). transfer elements between them (Figure 55.13). The nutrients
in living organisms and detritus (reservoir A) are available to
Biogeochemical Cycles other organisms when consumers feed and when detritivores
consume nonliving organic matter. The low pH and low
Because nutrient cycles involve both biotic and abiotic com- oxygen levels found in the waterlogged sediments of swamps
ponents, they are called biogeochemical cycles. We can can inhibit decomposition, leading to the formation of peat.
recognize two general scales of biogeochemical cycles: global When this occurs, organic materials from dead organisms
and local. Gaseous forms of carbon, oxygen, sulfur, and nitro- can be transferred from reservoir A to reservoir B; eventually,
gen occur in the atmosphere, and cycles of these elements peat may be converted to fossil fuels such as coal or oil.
are essentially global. For example, some of the carbon and Inorganic materials that are dissolved in water or present in
oxygen atoms a plant acquires from the air as CO2 may have soil or air (reservoir C) are available for use. Although most
been released into the atmosphere by the respiration of an organisms cannot directly tap into the inorganic elements
organism in a distant locale. Other elements, including phos- tied up in rocks (reservoir D), these nutrients may slowly
phorus, potassium, and calcium, are too heavy to occur as become available through weathering and erosion.
gases at Earth’s surface, although they are transported in dust.
In terrestrial ecosystems, these elements cycle more locally, Figure 55.14 provides a detailed look at the cycling of
absorbed from the soil by plant roots and eventually returned water, carbon, nitrogen, and phosphorus. When you study
each cycle, consider which steps are driven primarily by

Figure 55.13  Visualizing Biogeochemical Cycles

A biogeochemical cycle diagram summarizes the movements of Cycle diagrams include a representation of the
reservoirs in which the chemical element is
a chemical element between living and nonliving components found. A reservoir can consist of either organic
or inorganic materials, and those materials
of the biosphere. This figure uses a generic model of nutrient may be either available for direct use by
organisms, or unavailable.
cycling to show what types of information

may be represented. Later, when Nutrient uptake, Reservoir A A cycle diagram also represents
you study Figure 55.14, notice photosynthesis Organic materials the movements of the chemical
how this information is available as element between reservoirs, usually
depicted in the specific nutrients with arrows. These movements
nutrient cycles. Living occur through biological, chemical,
or geologic processes.
organisms, Waterlogging,
Respiration, detritus fossilization
decomposition,
excretion

Reservoir C 1 Suppose decomposition
Inorganic materials rates slowed greatly.
available as nutrients
Use the diagram to

Reservoir B hypothesize how that
Organic materials
Nutrient cycle diagrams Atmosphere unavailable as might affect the
may not represent the time nutrients
transfer of materials
Peat
scale of the different Coal from reservoir A to

processes. Thus, it’s Water Oil reservoirs B and C.

important to keep in mind Soil Burning of
that some processes, such as fossil fuels
photosynthesis, occur on a
short time scale within an Reservoir D
individual’s lifespan, while Inorganic materials
others, such as rock formation, Weathering, unavailable
occur on a long geologic erosion as nutrients

time scale. Formation of Minerals
in rocks
2 Compare and contrast the time sedimentary rock
scales at which materials move


into and out of reservoirs A and B. Instructors: Additional questions related
to this Visualizing Figure can be assigned
in MasteringBiology.

chapter 55  Ecosystems and Restoration Ecology 1247

Figure 55.14  Exploring Water and Nutrient Cycling

Examine each cycle closely, considering the major reservoirs of water, carbon,
nitrogen, and phosphorus and the processes that drive each cycle. The widths
of the arrows in the diagrams approximately reflect the relative contribution
of each process to the movement of water or a nutrient in the biosphere.

The Water Cycle

Biological importance Water is essential to all organisms, Movement over
and its availability influences the rates of ecosystem processes, land by wind
particularly primary production and decomposition in
terrestrial ecosystems. Precipitation Evaporation Precipitation
Forms available to life All organisms are capable of over ocean from ocean over land
exchanging water directly with their environment. Liquid water Percolation
is the primary physical phase in which water is used, though Evapotranspiration through
some organisms can harvest water vapor. Freezing of soil water from land soil
can limit water availability to terrestrial plants.
Reservoirs The oceans contain 97% of the water in the Runoff and
biosphere. Approximately 2% is bound in glaciers and polar groundwater
ice caps, and the remaining 1% is in lakes, rivers, and
groundwater, with a negligible amount in the atmosphere.
Key processes The main processes driving the water
cycle are evaporation of liquid water by solar energy,
condensation of water vapor into clouds, and precipitation.
Transpiration by terrestrial plants also moves large volumes
of water into the atmosphere. Surface and groundwater flow
can return water to the oceans, completing the water cycle.

The Carbon Cycle

CO2 in atmosphere Biological importance Carbon forms the framework of
Photosynthesis the organic molecules essential to all organisms.
Forms available to life Photosynthetic organisms utilize
Photo- Cellular CO2 during photosynthesis and convert the carbon to organic
synthesis respiration forms that are used by consumers, including animals, fungi,
and heterotrophic protists and prokaryotes.
Burning of Reservoirs The major reservoirs of carbon include fossil
fossil fuels fuels, soils, the sediments of aquatic ecosystems, the oceans
and wood (dissolved carbon compounds), plant and animal biomass, and
the atmosphere (CO2). The largest reservoir is sedimentary
Phyto- rocks such as limestone; however, carbon remains in this pool
plankton for long periods of time. All organisms are capable of returning
carbon directly to their environment in its original form (CO2)
Consumers through respiration.
Key processes Photosynthesis by plants and phytoplankton
Consumers removes substantial amounts of atmospheric CO2 each year.
This quantity is approximately equal to the CO2 added to the
Decomposition atmosphere through cellular respiration by producers and
consumers. The burning of fossil fuels and wood is adding
significant amounts of additional CO2 to the atmosphere. Over
geologic time, volcanoes are also a substantial source of CO2.

BioFlix® Animation: The Carbon Cycle

1248 Unit eight  Ecology

The Nitrogen Cycle

Biological importance Nitrogen is part of amino acids, proteins, Forms available to life Plants can assimilate (use) two inorganic
and nucleic acids and is often a limiting plant nutrient. forms of nitrogen—ammonium (NH4+) and nitrate (NO3–)—and
some organic forms, such as amino acids. Various bacteria can use
all of these forms as well as nitrite (NO2–). Animals can use only
organic forms of nitrogen.

N2 in atmosphere Reservoirs The main reservoir of nitrogen is the atmosphere,
Reactive N which is 80% free nitrogen gas (N2). The other reservoirs of
gases inorganic and organic nitrogen compounds are soils and the
sediments of lakes, rivers, and oceans; surface water and
Industrial groundwater; and the biomass of living organisms.
fixation

Key processes The major pathway for nitrogen to enter an ecosys-
tem is via nitrogen fixation, the conversion of N2 to forms that can be
Denitrification used to synthesize organic nitrogen compounds. Certain bacteria, as

N fertilizers well as lightning and volcanic activity, fix nitrogen naturally. Nitrogen
inputs from human activities now outpace natural inputs on land.
Fixation Two major contributors are industrially produced fertilizers and

Dissolved Runoff legume crops that fix
organic N NO3– nitrogen via bacteria in
NO3– Terrestrial N2 their root nodules. Other
NH4+ cycling
Aquatic
cycling bacteria in soil convert
nitrogen to different
Denitri- forms. Examples include
fication nitrifying bacteria, which

Decomposition Assimilation convert ammonium to
and
Decomposition nitrate, and denitrifying
sedimentation Fixation in bacteria, which convert
root nodules nitrate to nitrogen gas.
Uptake NO3– Human activities also
of amino release large quantities of
reactive nitrogen gases,
acids such as nitrogen oxides,

Ammoni- Nitrification
fication
NH4+
Animation: The Nitrogen Cycle
to the atmosphere.

The Phosphorus Cycle

Biological importance Organisms require phosphorus as a Wind-blown
major constituent of nucleic acids, phospholipids, and ATP and dust
other energy-storing molecules and as a mineral constituent of
bones and teeth. Geologic Weathering
Forms available to life The most biologically important uplift of rocks
inorganic form of phosphorus is phosphate (PO43–), which plants
absorb and use in the synthesis of organic compounds. Runoff
Reservoirs The largest accumulations of phosphorus are in
sedimentary rocks of marine origin. There are also large quantities Consumption
of phosphorus in soil, in the oceans (in dissolved form), and in
organisms. Because soil particles bind PO43–, the recycling of Decomposition Plant
phosphorus tends to be quite localized in ecosystems. uptake
Key processes Weathering of rocks gradually adds PO43– to Plankton Dissolved PO43– of PO43–
soil; some leaches into groundwater and surface water and
may eventually reach the sea. Phosphate taken up by producers Uptake Leaching
and incorporated into biological molecules may be eaten by
consumers. Phosphate is returned to soil or water by either Sedimentation
decomposition of biomass or excretion by consumers. Because
there are no significant phosphorus-containing gases, only Decomposition
relatively small amounts of phosphorus move through the
atmosphere, usually in the forms of dust and sea spray.

chapter 55  Ecosystems and Restoration Ecology 1249

biological processes. For the carbon cycle, for instance, plants, the mineral nutrients in the system. For example, only about

animals, and other organisms control most of the key steps, 0.3% more calcium (Ca2+) leaves a valley via its creek than

including photosynthesis and decomposition. For the water is added by rainwater, and this small net loss is probably

cycle, however, purely physical processes control many key replaced by chemical decomposition of the bedrock. During

steps, such as evaporation from the oceans. Note also that most years, the forest even registers small net gains of a few

human actions, such as the burning of fossil fuels and the mineral nutrients, including nitrogen.

production of fertilizers, have had major effects on the global Experimental deforestation of a watershed dramatically

cycling of carbon and nitrogen. increased the flow of water and minerals leaving the water-

How have ecologists worked out the details of chemical shed (Figure 55.15b). Over three years, water runoff from

cycling in various ecosystems? One common method is to the newly deforested watershed was 30–40% greater than in

follow the movement of naturally occurring, nonradioactive a control watershed, apparently because there were no plants

isotopes through the biotic (organic) and abiotic (inorganic) to absorb and transpire water from the soil. Most remark-

components of an ecosystem. Another method involves add- able was the loss of nitrate, whose concentration in the creek

ing tiny amounts of radioactive isotopes of specific elements increased 60-fold, reaching levels considered unsafe for drink-

and tracing their progress. Scientists have also been able to ing water (Figure 55.15c). The Hubbard Brook deforestation

make use of radioactive carbon (14C) released into the atmo- study showed that the amount of nutrients leaving an intact

sphere during atom bomb testing in the

1950s and early 1960s. This “spike” of Figure 55.15  Nutrient cycling in the Hubbard Brook Experimental Forest: an
14C can reveal where and how quickly example of long-term ecological research.

carbon flows into ecosystem compo-

nents, including plants, soils, and

ocean water.

Case Study: Nutrient Cycling (a) Concrete dams and weirs (b) One watershed was clear-cut to study the effects of the loss of
in the Hubbard Brook built across streams at the vegetation on drainage and nutrient cycling. All of the original
Experimental Forest bottom of watersheds plant material was left in place to decompose.
enabled researchers to
Since 1963, ecologist Gene Likens and monitor the out ow of
colleagues have been studying nutri- water and nutrients from
ent cycling at the Hubbard Brook the ecosystem.
Experimental Forest in the White
Mountains of New Hampshire. Their Nitrate concentration in runoff 80 Deforested
research site is a deciduous forest that (mg/L) 60
grows in six small valleys, each drained 40 Control
by a single creek. Impermeable bedrock 20 1967
underlies the soil of the forest.
4 Completion of
The research team first determined 3 tree cutting
the mineral budget for each of six
valleys by measuring the input and 2
outflow of several key nutrients. They
collected rainfall at several sites to mea- 1
sure the amount of water and dissolved
minerals added to the ecosystem. To 0 1966 1968
monitor the loss of water and miner- 1965
als, they constructed a small concrete
dam with a V-shaped spillway across (c) The concentration of nitrate in runoff from the deforested watershed was 60 times greater than
the creek at the bottom of each valley in a control (unlogged) watershed.
(Figure 55.15a). They found that about Instructors: A related Experimental Inquiry Tutorial can be assigned in MasteringBiology.
60% of the water added to the ecosys-
tem as rainfall and snow exits through
the stream, and the remaining 40% is
lost by evapotranspiration.

Preliminary studies confirmed that
internal cycling conserved most of

1250 unit eight  Ecology

forest ecosystem is controlled mainly by the plants. Retaining environmental damage is at least partly reversible. This optimis-
nutrients in an ecosystem helps to maintain the productivity tic view must be balanced by a second assumption—that ecosys-
of the system, as well as to avoid algal blooms and other prob- tems are not infinitely resilient. Restoration ecologists therefore
lems caused by excess nutrient runoff. work to identify and manipulate the processes that most limit
recovery of ecosystems from disturbances. Where disturbance is
Interview with Eugene Likens: Co-founder of the Hubbard so severe that restoring all of a habitat is impractical, ecologists
Brook Forest Study try to reclaim as much of a habitat or ecological process as pos-
sible, within the limits of the time and money available to them.
Concept Check 55.4
In extreme cases, the physical structure of an ecosystem
1. DRAW IT For each of the four biogeochemical cycles in may need to be restored before biological restoration can
Figure 55.14, draw a simple diagram that shows one pos- occur. If a stream was straightened to channel water quickly
sible path for an atom of that chemical from abiotic to through a suburb, ecologists may reconstruct a meandering
biotic reservoirs and back. channel to slow down the flow of water eroding the stream
bank. To restore an open-pit mine, engineers may grade
2. Why does deforestation of a watershed increase the con- the site with heavy equipment to reestablish a gentle slope,
centration of nitrates in streams draining the watershed? spreading topsoil when the slope is in place (Figure 55.16).

3. WHAT IF? Why is nutrient availability in a tropical rain After any physical reconstruction of the ecosystem is com-
forest particularly vulnerable to logging? plete, the next step is biological restoration. The long-term
objective of restoration is to return an ecosystem as closely
For suggested answers, see Appendix A. as possible to its predisturbance state. Figure 55.17 explores
four ambitious and successful restoration projects. These and
Concept  55.5 the many other such projects throughout the world often
employ two key strategies: bioremediation and biological
Restoration ecologists return degraded augmentation.
ecosystems to a more natural state
Bioremediation
Ecosystems can recover naturally from most disturbances
(including the experimental deforestation at Hubbard Brook) Using organisms—usually prokaryotes, fungi, or plants—to
through the stages of ecological succession (see Concept 54.3). detoxify polluted ecosystems is known as bioremediation.
Sometimes, however, that recovery takes centuries, particu- Some plants and lichens adapted to soils containing heavy
larly when humans have degraded the environment. Tropical metals can accumulate high concentrations of toxic metals
areas that are cleared for farming may quickly become unpro- such as lead and cadmium in their tissues. Restoration ecolo-
ductive because of nutrient losses. Mining activities may last gists can introduce such species to sites polluted by mining
for several decades, and the lands are often abandoned in a and other human activities and then harvest these organ-
degraded state. Ecosystems can also be damaged by salts that isms to remove the metals from the ecosystem. For instance,
build up in soils from irrigation and by toxic chemicals or oil researchers in the United Kingdom have discovered a lichen
spills. Biologists increasingly are called on to help restore and
repair damaged ecosystems.

Restoration ecologists seek to initiate or speed up the recov-
ery of degraded ecosystems. One of the basic assumptions is that

Figure 55.16  A gravel and clay mine site in New Jersey before and after restoration.

(a) In 1991, before restoration (b) In 2000, near the completion of restoration

chapter 55  Ecosystems and Restoration Ecology 1251

Figure 55.17  Exploring Restoration Ecology Worldwide

The examples highlighted in this figure are just a few of the many
restoration ecology projects taking place around the world.

Kissimmee River, Florida

In the 1960s, the Kissimmee River was 167 km of natural river channel. Pictured
converted from a meandering river to here is a section of the Kissimmee canal
a 90-km canal to control flooding. This that has been plugged (wide, light strip
channelization diverted water from the on the right side of the photo), diverting
floodplain, causing the wetlands to dry up, flow into remnant river channels (center
threatening many fish and wetland bird of the photo). The project will also
populations. Kissimmee River restoration restore natural flow patterns, which
has filled 12 km of drainage canal and will foster self-sustaining populations of
reestablished 24 km of the original wetland birds and fishes.

Succulent Karoo, South Africa

In the Succulent Karoo desert region employing more sustainable resource
of southern Africa, as in many arid management. The photo shows a small
regions, overgrazing by livestock has sample of the exceptional plant diversity
damaged vast areas. Private landowners of the Succulent Karoo; its 5,000 plant
and government agencies in South species include the highest diversity of
Africa are restoring large areas of this succulent plants in the world.
unique region, revegetating the land and

Maungatautari, New Zealand

Weasels, rats, pigs, and other introduced the reserve eliminates the need to
species pose a serious threat to New continue setting traps and using
Zealand’s native plants and animals, poisons that can harm native wildlife.
including kiwis, a group of flightless, In 2006, a pair of critically endangered
ground-dwelling bird species. The goal takahe (a species of flightless rail) were
of the Maungatautari restoration project released into the reserve with the hope
is to exclude all exotic mammals from a of reestablishing a breeding population
3,400-ha reserve located on a forested of this colorful bird on New Zealand’s
volcanic cone. A specialized fence around North Island.

Coastal Japan Techniques include constructing suitable
seafloor habitat, transplanting seaweeds and
Seaweed and seagrass beds are important seagrasses from natural beds using artificial
nursery grounds for a wide variety of fishes substrates, and hand seeding (shown in this
and shellfish. Once extensive but now photograph).
reduced by development, these beds are
being restored in the coastal areas of Japan.

species that grows on soil polluted with uranium dust left Concentration ofFigure 55.18  Bioremediation of groundwater
over from mining. The lichen concentrates uranium in a dark soluble uranium (μM )contaminated with uranium at Oak Ridge National
pigment, making it useful as a biological monitor and poten- Laboratory, Tennessee.
tially as a remediator.
(a) Wastes containing uranium were dumped in these four unlined pits
Ecologists already use the abilities of many prokaryotes to for more than 30 years, contaminating soils and groundwater.
carry out bioremediation of soils and water (see Concept 27.6). 6
Scientists have sequenced the genomes of at least ten prokary- 5
otic species specifically for their bioremediation potential. One 4
of the species, the bacterium Shewanella oneidensis, appears 3
particularly promising. It can metabolize a dozen or more ele- 2
ments under aerobic and anaerobic conditions. In doing so, it 1
converts soluble forms of uranium, chromium, and nitrogen 0
to insoluble forms that are less likely to leach into streams or 0 50 100 150 200 250 300 350 400
groundwater. Researchers at Oak Ridge National Laboratory, Days after adding ethanol
in Tennessee, stimulated the growth of Shewanella and other
uranium-reducing bacteria by adding ethanol to groundwater (b) After ethanol was added, microbial activity decreased the
contaminated with uranium; the bacteria can use ethanol as an concentration of soluble uranium in groundwater near the pits.
energy source. In just five months, the concentration of solu-
ble uranium in the ecosystem dropped by 80% (Figure 55.18). Ecosystems: A Review

Biological Augmentation Figure 55.19 illustrates energy transfer, nutrient cycling,
and other key processes for an arctic tundra ecosystem. Note
In contrast to bioremediation, which is a strategy for remov- the conceptual similarities between this figure and Make
ing harmful substances from an ecosystem, biological Connections Figure 10.23, “The Working Cell.” The scale of
augmentation uses organisms to add essential materials the two figures is different, but the physical laws and biological
to a degraded ecosystem. To augment ecosystem processes, rules that govern life apply equally to both systems.
restoration ecologists need to determine which factors, such
as chemical nutrients, have been lost from a system and are Concept Check 55.5
limiting its recovery.
1. Identify the main goal of restoration ecology.
Encouraging the growth of plants that thrive in nutrient- 2. WHAT IF? In what way is the Kissimmee River proj-
poor soils often speeds up succession and ecosystem recovery.
In alpine ecosystems of the western United States, nitrogen- ect a more complete ecological restoration than the
fixing plants such as lupines are often planted to raise nitrogen Maungatautari project (see Figure 55.17)?
concentrations in soils disturbed by mining and other activi-
ties. Once these nitrogen-fixing plants become established, For suggested answers, see Appendix A.
other native species are better able to obtain enough soil
nitrogen to survive. In other systems where the soil has been
severely disturbed or where topsoil is missing entirely, plant
roots may lack the mycorrhizal symbionts that help them meet
their nutritional needs (see Concept 31.1). Ecologists restoring
a tallgrass prairie in Minnesota recognized this limitation and
enhanced the recovery of native species by adding mycorrhizal
symbionts to the soil they seeded.

Restoring the physical structure and plant community
of an ecosystem does not always ensure that animal species
will recolonize a site and persist there. Because animals pro-
vide critical ecosystem services, including pollination and
seed dispersal, restoration ecologists sometimes help wildlife
to reach and use restored ecosystems. They might release
animals at a site or establish habitat corridors that connect
a restored site to places where the animals are found. They
sometimes establish artificial perches for birds to use. These
and other efforts can increase the biodiversity of restored
ecosystems and help the community persist.

chapter 55  Ecosystems and Restoration Ecology 1253

Figure 55.19 Make Connections

The Working Ecosystem

This arctic tundra ecosystem teems with life in the short
two-month growing season each summer. In ecosystems,
organisms interact with each other and with the environment
around them in diverse ways, including those illustrated here.

1 2
Caribou Snow geese

Populations Are Dynamic (Chapter 53) 5
Herbivory
1 Populations change in size through births and
deaths and through immigration and
emigration. Caribou migrate across the
tundra to give birth at their calving grounds
each year. (See Figure 53.3.)

2 Snow geese and many other species migrate
to the Arctic each spring for the abundant food
found there in summer. (See Concept 51.1.)

3 Birth and death rates influence the density of all
populations. Death in the tundra comes from
many causes, including predation, competition
for resources, and lack of food in winter.
(See Figure 53.18.)

BioFlix® Animation: Population Ecology

Arctic fox 3 Species Interact in Diverse Ways (Chapter 54)

4 4 In predation, an individual of one species kills
Predation and eats another. (See Concept 54.1.)

Snow goose 5 In herbivory, an individual of one species eats part of
a plant or other primary producer, such as a caribou
eating a lichen. (See Concept 54.1.)

6 In mutualism, two species interact in ways that benefit
each other. In some mutualisms, the partners live in
direct contact, forming a symbiosis; for example, a
lichen is a symbiotic mutualism between a fungus and
an alga or cyanobacterium. (See Concept 54.1 and
Figures 31.22 and 31.23.)

7 In competition, individuals seek to acquire the same
limiting resources. For example, snow geese and caribou
both eat cottongrass. (See Concept 54.1.)

1254

Nitrogen cycle 12 Carbon cycle Organisms Transfer Energy and Matter
N2 CO2 in Ecosystems (Chapter 55)

Denitrification Cellular 8 Primary producers convert the energy in sunlight
respiration to chemical energy through photosynthesis. Their
Photosynthesis growth is often limited by abiotic factors such as
low temperatures, scarce soil nutrients, and lack of
Organisms N fixation light in winter. (See Figures 10.6, 52.12, and 55.4.)

9 Food chains are typically short in the tundra
because primary production is lower than in most
other ecosystems. (See Figure 54.14.)

10 When one organism eats another, the transfer of
energy from one trophic level to the next is typically
only 10%. (See Figure 55.10.)

11 Detritivores recycle chemical elements back to
primary producers. (See Figures 55.3 and 55.4.)

12 Chemical elements such as carbon and nitrogen
move in cycles between the physical environment
and organisms. (See Figures 55.13 and 55.14.)

BioFlix® Animation: The Carbon Cycle

Secondary 10
consumers
(wolves)
9

Primary
consumers
(caribou)

Primary Chemical elements
producers
(plants and lichens)

7 Competition 8 Detritivores
(soil fungi and
6 Mutualism 11 prokaryotes)

Algal cell Lichen
Fungal
hyphae

MAKE CONNECTIONS Human actions are causing
climate change, thereby affecting Earth’s ecosystems—
few of which have been affected as greatly as those in the
Arctic. Hypothesize how climate change might cause evo-
lution in arctic tundra populations. Explain. (See Concepts
1.1, 22.2, and 25.4.)

1255

55 Chapter Review Go to MasteringBiology™ for Videos, Animations, Vocab Self-Quiz,
Practice Tests, and more in the Study Area.

Summary of Key Concepts Concept  55.3

Concept  55.1 Energy transfer between trophic levels
is typically only 10% efficient (pp. 1244–1246)

Physical laws govern energy flow The amount of energy available to each trophic level is determined
by the net primary production and the production efficiency,
and chemical cycling in ecosystems the efficiency with which food energy is converted to biomass at
each link in the food chain.
(pp. 1237–1239) VOCAB
SELF-QUIZ The percentage of energy transferred from one trophic level to the
goo.gl/6u55ks next, called trophic efficiency, is typically 10%. Pyramids of
An ecosystem consists of all the organisms in a energy and biomass reflect low trophic efficiency.
community and all the abiotic factors with which
they interact. Energy is conserved but released as heat during
ecosystem processes. As a result, energy flows through ecosystems
(rather than being recycled). Tertiary
Chemical elements enter and leave an ecosystem and cycle consumers 10 J

within it, subject to the law of conservation of mass. Inputs
and outputs are generally small compared to recycled amounts,
but their balance determines whether the ecosystem gains or Secondary 100 J
consumers

loses an element over time.

Loss of heat Sun Key Primary 1,000 J
Primary producers consumers 10,000 J
Chemical cycling Primary 1,000,000 J of sunlight
Energy flow producers

Primary consumers Detritus ? Why would runners have a lower production efficiency when running a
Secondary and Microorganisms long-distance race than when they are sedentary?

tertiary consumers and other Concept  55.4
detritivores
Biological and geochemical processes cycle
nutrients and water in ecosystems (pp. 1246–1251)

? Considering the second law of thermodynamics, would you expect the Water moves in a global cycle driven by solar energy. The car-
typical biomass of primary producers in an ecosystem to be greater bon cycle primarily reflects the reciprocal processes of photo-
synthesis and cellular respiration. Nitrogen enters ecosystems
than or less than the biomass of secondary producers in the system? through atmospheric deposition and nitrogen fixation by
prokaryotes.
Explain your reasoning.
The proportion of a nutrient in a particular form varies
Concept  55.2 among ecosystems, largely because of differences in the rate of
decomposition.
Energy and other limiting factors
control primary production in ecosystems Nutrient cycling is strongly regulated by vegetation. The
(pp. 1239–1243) Hubbard Brook case study showed that logging increases water
runoff and can cause large losses of minerals.
Primary production sets the spending limit for the global
energy budget. Gross primary production is the total energy ? If decomposers usually grow faster and decompose material more quickly
assimilated by an ecosystem in a given period. Net primary in warmer ecosystems, why is decomposition in hot deserts relatively slow?
production, the energy accumulated in autotroph biomass,
equals gross primary production minus the energy used by the Concept  55.5
primary producers for respiration. Net ecosystem production
is the total biomass accumulation of an ecosystem, defined as the Restoration ecologists return degraded
difference between gross primary production and total ecosystem ecosystems to a more natural state (pp. 1251–1255)
respiration.
Restoration ecologists harness organisms to detoxify polluted
In aquatic ecosystems, light and nutrients limit primary produc- ecosystems through the process of bioremediation.
tion. In terrestrial ecosystems, climatic factors such as tempera-
ture and moisture affect primary production at large scales, but a In biological augmentation, ecologists use organisms to add
soil nutrient is often the limiting factor locally. essential materials to ecosystems.

? If you know NPP for an ecosystem, what additional variable do you be ? In preparing a site for surface mining and later restoration, why would
need to know to estimate NEP? Why might measuring this variable engineers separate the topsoil from the deeper soil, rather than removing

difficult, for instance, in a sample of ocean water? all soil at once and mixing it in a single pile?

1256 Unit eight  Ecology

Test Your Understanding Level 3: Synthesis/Evaluation

Level 1: Knowledge/Comprehension 9. DRAW IT  (a) Draw a simplified global water cycle showing
ocean, land, atmosphere, and runoff from the land to the
1. Which of the following organisms is incorrectly PRACTICE ocean. Label your drawing with these annual water fluxes:
paired with its trophic level? TEST     ocean evaporation, 425 km3
(A) cyanobacterium—primary producer      ocean evaporation that returns to the ocean as precipitation,
(B) grasshopper—primary consumer goo.gl/CUYGKD 385 km3
(C) zooplankton—primary producer      ocean evaporation that falls as precipitation on land, 40 km3
(D) fungus—detritivore      evapotranspiration from plants and soil that falls as precipi-
tation on land, 70 km3
2. Which of these ecosystems has the lowest net primary     runoff to the oceans, 40 km3
production per square meter? (b) What is the ratio of ocean evaporation that falls as precipitation
(A) a salt marsh on land compared with runoff from land to the oceans? (c) How
(B) an open ocean would this ratio change during an ice age, and why?
(C) a coral reef
(D) a tropical rain forest 10. EVOLUTION CONNECTION  Some biologists have suggested
that ecosystems are emergent, “living” systems capable of
3. The discipline that applies ecological principles to returning evolving. One manifestation of this idea is environmentalist
degraded ecosystems to a more natural state is known as James Lovelock’s Gaia hypothesis, which views Earth itself as
(A) restoration ecology. a living, homeostatic entity—a kind of superorganism. Are
(B) thermodynamics. ecosystems capable of evolving? If so, would this be a form of
(C) eutrophication. Darwinian evolution? Why or why not? Explain.
(D) biogeochemistry.
11. SCIENTIFIC INQUIRY  Using two neighboring ponds in a forest
Level 2: Application/Analysis as your study site, design a controlled experiment to measure
the effect of falling leaves on net primary production in a pond.
4. Nitrifying bacteria participate in the nitrogen cycle mainly by
(A) converting nitrogen gas to ammonia. 12. WRITE ABOUT A THEME: Energy and Matter 
(B) releasing ammonium from organic compounds, thus Decomposition typically occurs quickly in moist tropical
returning it to the soil. forests. However, waterlogging in the soil of some moist
(C) converting ammonium to nitrate, which plants absorb. tropical forests results over time in a buildup of organic
(D) incorporating nitrogen into amino acids and organic matter called “peat.” In a short essay (100–150 words), discuss
compounds. the relationship of net primary production, net ecosystem
production, and decomposition for such an ecosystem. Are
5. Which of the following has the greatest effect on the rate of NPP and NEP likely to be positive? What do you think would
chemical cycling in an ecosystem? happen to NEP if a landowner drained the water from a
(A) the rate of decomposition in the ecosystem tropical peatland, exposing the organic matter to air?
(B) the production efficiency of the ecosystem’s consumers
(C) the trophic efficiency of the ecosystem 13. SYNTHESIZE YOUR KNOWLEDGE
(D) the location of the nutrient reservoirs in the ecosystem
This dung beetle (genus Scarabaeus) is burying a ball of dung
6. The Hubbard Brook watershed deforestation experiment it has collected from a large mammalian herbivore in Kenya.
yielded all of the following results except which of the Explain why this process is important for the cycling of nutri-
following? ents and for primary production.
(A) Most minerals were recycled within a forest ecosystem. For selected answers, see Appendix A.
(B) Calcium levels remained high in the soil of deforested
areas. For additional practice questions, check out the Dynamic Study
(C) Deforestation increased water runoff. Modules in MasteringBiology. You can use them to study on
(D) The nitrate concentration in waters draining the deforested your smartphone, tablet, or computer anytime, anywhere!
area became dangerously high.

7. Which of the following would be considered an example of
bioremediation?
(A) adding nitrogen-fixing microorganisms to a degraded
ecosystem to increase nitrogen availability
(B) using a bulldozer to regrade a strip mine
(C) reconfiguring the channel of a river
(D) adding seeds of a chromium-accumulating plant to soil
contaminated by chromium

8. If you applied a fungicide to a cornfield, what would you expect
to happen to the rate of decomposition and net ecosystem
production (NEP)?
(A) Both decomposition rate and NEP would decrease.
(B) Neither would change.
(C) Decomposition rate would increase and NEP would
decrease.
(D) Decomposition rate would decrease and NEP would
increase.

chapter 55  Ecosystems and Restoration Ecology 1257

Conservation Biology 56
and Global Change

Figure 56.1  What will be the fate of this newly described lizard species?

Key Concepts Psychedelic Treasure

56.1 Human activities threaten Earth’s Scurrying across a rocky outcrop, a lizard stops abruptly in a patch of sunlight. It catches
the eye of a conservation biologist, who is thrilled to observe the gecko splashed with
biodiversity rainbow colors, its bright orange legs and tail blending into a blue body, its head and
neck splotched with yellow and green. This lizard, the psychedelic rock gecko (Cnemaspis
56.2 Population conservation focuses psychedelica), was discovered in 2010 during an expedition to the Greater Mekong region
of southeast Asia (Figure 56.1). Its known habitat is restricted to an island of just 8 km2
on population size, genetic (3 mi2) in southern Vietnam. Other new species found during the same series of expe-
diversity, and critical habitat ditions include the striking Daklak orchid (Dendrobium daklakense), named for the
Vietnamese province where it was observed. Between 2000 and 2010, biologists identi-
56.3 Landscape and regional fied more than 1,000 new species in the Greater Mekong region alone.

conservation help sustain To date, scientists have described and formally named about 1.8 million species
biodiversity of organisms. In addition to these named species, many others remain to be discov-
ered: Estimates for the number of species that currently exist range from 5 million
56.4 Earth is changing rapidly to 100 million. Some of the greatest concentrations of species are in the tropics.
Unfortunately, tropical forests are being cleared at an alarming rate to make room for
as a result of human actions and support a burgeoning human population. Rates of deforestation in Vietnam are
among the highest in the world (Figure 56.2). What will become of the psychedelic
56.5 Sustainable development can rock gecko and other newly discovered species if such activities continue unchecked?

improve human lives while Daklak orchid
conserving biodiversity

When you see this blue icon, log in to MasteringBiology Get Ready for This Chapter
and go to the Study Area for digital resources.

Figure 56.2  Tropical deforestation in Vietnam. These hills rate seen in the fossil record (see Concept 25.4). This compari-
were once covered with tropical forest, most of which has been cut son suggests that the extinction rate today is high and that
down to make room for farmland such as the terraced rice fields on human activities threaten Earth’s biodiversity at all levels.
the lower slopes.
Three Levels of Biodiversity
Throughout the biosphere, human activities are altering
natural disturbances, trophic structures, energy flow, and Biodiversity—short for biological diversity—can be considered
chemical cycling—ecosystem processes on which we and all at three main levels: genetic diversity, species diversity, and
other species depend. We have physically altered nearly half of ecosystem diversity (Figure 56.3).
Earth’s land surface, and we use over half of all accessible sur-
face fresh water. In the oceans, stocks of most major fisheries Genetic Diversity
are shrinking because of overharvesting. By some estimates,
we may be pushing more species toward extinction than did Genetic diversity comprises not only the individual genetic
the asteroid that triggered the Cretaceous mass extinction variation within a population, but also the genetic variation
66 million years ago (see Figure 25.18). between populations that is often associated with adaptations
to local conditions. If one population becomes extinct, then
In this chapter, we’ll examine changes happening across a species may have lost some of the genetic diversity that
Earth, focusing on conservation biology, a discipline that makes microevolution possible. This erosion of genetic diver-
integrates ecology, physiology, molecular biology, genetics, sity in turn reduces the adaptive potential of the species.
and evolutionary biology to conserve biological diversity at
all levels. Efforts to sustain ecosystem processes and stem the Figure 56.3  Three levels of biodiversity. The oversized
loss of biodiversity also connect the life sciences with the chromosomes in the top diagram symbolize the genetic variation
social sciences, economics, and humanities. within the population.

We’ll begin by taking a closer look at the biodiversity Genetic diversity in a vole population
crisis and examining some of the conservation strategies
being adopted to slow the rate of species loss. We’ll also Species diversity in a coastal redwood ecosystem
examine how human activities are altering the environment
through climate change, ozone depletion, and other global Community and ecosystem diversity
processes. Finally, we’ll consider how current decisions about across the landscape of an entire region
long-term conservation priorities could affect life on Earth.

Concept  56.1

Human activities threaten Earth’s
biodiversity

Extinction is a natural phenomenon that has been occurring
since life first evolved; it is the high rate of extinction that is
responsible for today’s biodiversity crisis. More than 1,000
species have become extinct in the last 400 years, a rate that
is 100 to 1,000 times the “background,” or typical, extinction

chapter 56  Conservation Biology and Global Change 1259

Species Diversity river system but survive in an adjacent one. Global extinction
of a species means that it is lost from all the ecosystems in
Public awareness of the biodiversity crisis centers on species which it lived, leaving them permanently impoverished.
diversity—the number of species in an ecosystem or across
the biosphere. Of particular concern are species that are HHMI Video: Surveying Gorongosa’s Biodiversity
endangered or threatened. An endangered species is one
that is in danger of extinction throughout all or much of its Ecosystem Diversity
range (Figure 56.4), while a threatened species is con-
sidered likely to become endangered in the near future. The The variety of ecosystems on Earth is a third level of bio-
following are just a few statistics that illustrate the problem logical diversity. Because of the many interactions between
of species loss: different species in an ecosystem, the extinction of popula-
tions of one species can have a negative impact on other
According to the International Union for Conservation species in the ecosystem (see Figure 54.18). For instance,
of Nature and Natural Resources (IUCN), 12% of the bats called “flying foxes” are important pollinators and seed
10,000 known species of birds and 21% of the 5,500 dispersers in the Pacific Islands, where they are increas-
known species of mammals are threatened. ingly hunted as a luxury food (Figure 56.5). Conservation
biologists fear that the extinction of flying foxes would also
A survey by the Center for Plant Conservation showed harm the native plants of the Samoan Islands, where four-
that of the nearly 20,000 known plant species in the fifths of the tree species depend on flying foxes for pollina-
United States, 200 have become extinct since such tion or seed dispersal.
records have been kept, and 730 are endangered or
threatened. Some ecosystems have already been heavily affected by
humans, and others are being altered at a rapid pace. Since
In North America, at least 123 freshwater animal species European colonization, more than half of the wetlands in the
have become extinct since 1900, and hundreds more contiguous United States have been drained and converted
species are threatened. The extinction rate for North to agricultural and other uses. In California, Arizona, and
American freshwater fauna is about five times as high New Mexico, roughly 90% of native riparian (streamside)
as that for terrestrial animals. communities have been affected by overgrazing, flood con-
trol, water diversions, lowering of water tables, and invasion
The local populations of a species can also be driven to extinc- by non-native plants.
tion; for example, populations of a species may be lost in one
Biodiversity and Human Welfare
Figure 56.4  A hundred heartbeats from extinction. These
are two members of what Harvard biologist E. O. Wilson calls the Why should we care about the loss of biodiversity? One basic
Hundred Heartbeat Club, species with fewer than 100 individuals reason concerns our human sense of connection to nature
remaining on Earth. The Yangtze River dolphin may be extinct, and all forms of life, termed biophilia. Moreover, the belief
but a few individuals were reportedly sighted in 2007. that other species are entitled to life is a pervasive theme

Philippine eagle Figure 56.5  The endangered Marianas “flying fox” bat
(Pteropus mariannus), an important pollinator.
Yangtze River
dolphin

? T o document that a species has actually become extinct, what factors
would you need to consider?

1260 unit eight  Ecology

of many religions and the basis of a moral argument that Each species lost means the loss of unique genes, some of
we should protect biodiversity. There is also a concern for which may code for enormously useful proteins. The enzyme
future human generations. Paraphrasing an old proverb, Taq polymerase was first extracted from a bacterium, Thermus
G. H. Brundtland, a former prime minister of Norway, said, aquaticus, found in hot springs at Yellowstone National Park.
“We must consider our planet to be on loan from our c­ hildren, This enzyme is essential for the polymerase chain reaction
rather than being a gift from our ancestors.” In addition (PCR) because it is stable at the high temperatures required
to such philosophical and moral justifications, species for automated PCR (see Figure 20.8). DNA from many other
and genetic diversity bring us many practical benefits. species of prokaryotes, living in a variety of environments, is
used in the mass production of proteins for new medicines,
Interview with E. O. Wilson: Advocate for protecting foods, petroleum substitutes, industrial chemicals, and other
biodiversity products. However, because many species of prokaryotes
and other organisms may become extinct before we discover
Benefits of Species and Genetic Diversity them, we stand to lose the valuable genetic potential held
in their unique libraries of genes.
Many threatened species could potentially provide medi-
cines, food, and fibers for human use, making biodiversity a Ecosystem Services
crucial natural resource. Products from aspirin to antibiotics
were derived originally from natural sources. If we lose wild The benefits that individual species provide to humans are
populations of plants closely related to agricultural species, substantial, but saving individual species is only part of the
we lose genetic resources that could be used to improve crop reason for preserving ecosystems. Humans evolved in Earth’s
qualities, such as disease resistance. For instance, in the 1970s, ecosystems, and we rely on these systems and their inhabit-
plant breeders responded to devastating outbreaks of the grassy ants for our survival. Ecosystem services encompass all
stunt virus in rice (Oryza sativa) by screening 7,000 popula- the processes through which natural ecosystems help sus-
tions of this species and its close relatives for resistance to the tain human life. Ecosystems purify our air and water. They
virus. One population of a single relative, Indian rice (Oryza detoxify and decompose our wastes and reduce the impacts of
nivara), was found to be resistant to the virus, and scientists extreme weather and flooding. The organisms in ecosystems
succeeded in breeding the resistance trait into commercial pollinate our crops, control pests, and create and preserve our
rice varieties. Today, the original disease-resistant population soils. Moreover, these diverse services are provided for free.
has apparently become extinct in the wild.
If we had to pay for them, how much would the services
In the United States, about 25% of the prescriptions of natural ecosystems be worth? In 1997, scientists esti-
dispensed from pharmacies contain substances originally mated the value of Earth’s ecosystem services at $33 trillion
derived from plants. For example, researchers discovered that per year, nearly twice the gross national product of all the
the rosy periwinkle, which grows in Madagascar, contains countries on Earth at the time ($18 trillion). It may be more
alkaloids that inhibit cancer cell growth (Figure 56.6). This realistic to do the accounting on a smaller scale. In 1996,
discovery led to treatments for two deadly forms of cancer, New York City invested more than $1 billion to buy land
Hodgkin’s lymphoma and childhood leukemia, resulting and restore habitat in the Catskill Mountains, the source of
in remission in most cases. Madagascar is also home to five much of the city’s fresh water. This investment was spurred
other species of periwinkles, one of which is approaching by increasing pollution of the water by sewage, pesticides,
extinction. Losing these species would mean the loss of any and fertilizers. By harnessing ecosystem services to purify
possible medicinal benefits they might offer. its water naturally, the city saved $8 billion it would have
otherwise spent to build a new water treatment plant and
Figure 56.6  $300 million a year to run the plant.
The rosy periwinkle
(Catharanthus There is growing evidence that the functioning of ecosys-
roseus), a plant tems, and hence their capacity to perform services, is linked
that saves lives. to biodiversity. As human activities reduce biodiversity,
we are reducing the capacity of the planet’s ecosystems to
perform processes critical to our own survival.

Threats to Biodiversity

Many different human activities threaten biodiversity on
local, regional, and global scales. The threats posed by these
activities include four major types: habitat loss, introduced
species, overharvesting, and global change.

chapter 56  Conservation Biology and Global Change 1261

Habitat Loss lost, often as a result of the dams, reservoirs, channel modifi-
cation, and flow regulation now affecting most of the world’s
Human alteration of habitat is the single greatest threat to rivers. For example, the more than 30 dams and locks built
biodiversity throughout the biosphere. Habitat loss has been along the Mobile River basin in the southeastern United
brought about by factors such as agriculture, urban develop- States changed river depth and flow. While providing the
ment, forestry, mining, and pollution. As discussed later in benefits of hydroelectric power and increased ship traffic,
this chapter, global climate change is already altering habitats these dams and locks also helped drive more than 40 species
today and will have an even larger effect later this century. of mussels and snails to extinction.
When no alternative habitat is available or a species is unable
to move, habitat loss may mean extinction. The IUCN impli- Introduced Species
cates destruction of habitat as a contributing cause for 73%
of the species that have become extinct, endangered, vulner- Introduced species, also called non-native or exotic species,
able, or rare in the last few hundred years. are those that humans move intentionally or accidentally
from the species’ native locations to new geographic regions.
Habitat loss and fragmentation may occur over immense Human travel by ship and airplane has accelerated the trans-
regions. Approximately 98% of the tropical dry forests of plant of species. Free from the predators, parasites, and patho-
Central America and Mexico have been cut down. The clear- gens that limit their populations in their native habitats, such
ing of tropical rain forest in the state of Veracruz, Mexico, transplanted species may spread rapidly through a new region.
mostly for cattle ranching, has resulted in the loss of more
than 90% of the original forest, leaving relatively small, Some introduced species disrupt their new community,
isolated patches of forest. Many other natural habitats have often by preying on native organisms or outcompeting native
also been fragmented by human activities (Figure 56.7). organisms for resources. For example, the brown tree snake
was accidentally introduced to the island of Guam from other
Habitat fragmentation often leads to species loss because parts of the South Pacific after World War II, as a “stowaway”
the smaller populations in habitat fragments have a higher in military cargo. Since then, 12 species of birds and 6 species
probability of extinction. Prairie covered about 800,000 hect- of lizards that the snakes ate have become extinct on Guam.
ares of southern Wisconsin when Europeans first arrived in In 1988, the devastating zebra mussel, a suspension-feeding
North America but occupies only 800 hectares today; most mollusc, was discovered in the Great Lakes of North America,
of the original prairie in this area is now used to grow crops. most likely introduced in the ballast water of ships arriving
Plant diversity surveys of 54 Wisconsin prairie remnants con- from Europe. Zebra mussels form dense colonies and have
ducted in 1948–1954 and 1987–1988 showed that the rem- disrupted freshwater ecosystems, threatening native aquatic
nants lost 8–60% of their plant species in the time between species. They have also clogged water intake structures, caus-
the two surveys. ing billions of dollars in damage to domestic and industrial
water supplies.
Habitat loss is also a major threat to aquatic biodiversity.
About 70% of coral reefs, among Earth’s most species-rich Humans have deliberately introduced many species with
aquatic communities, have been damaged by human activi- good intentions but disastrous effects. An Asian plant called
ties. At the current rate of destruction, 40–50% of the reefs, kudzu, which the U.S. Department of Agriculture once intro-
home to one-third of marine fish species, could disappear duced in the southern United States to help control erosion,
in the next 30 to 40 years. Freshwater habitats are also being has taken over large areas of the landscape there (Figure 56.8).

Figure 56.7  Habitat fragmentation in the foothills of Los Figure 56.8  Kudzu, an introduced species, thriving
Angeles. Development in the valleys may confine the organisms that in the southeastern United States.
inhabit the narrow strips of hillside.

1262 unit eight  Ecology

The European starling was brought intentionally into New Figure 56.9  Ecological forensics and elephant poaching.
York’s Central Park in 1890 by a citizens’ group intent These severed tusks were part of an illegal shipment of ivory
on introducing all the plants and animals mentioned in intercepted on its way from Africa to Singapore in 2002. DNA-based
Shakespeare’s plays. It quickly spread across North America, evidence showed that the thousands of elephants killed for the tusks
where its population now exceeds 100 million, displacing came from a relatively narrow east-west band centered in Zambia
many native songbirds. rather than from across Africa.

Introduced species are a worldwide problem, contributing MAKE CONNECTIONS Figure 26.6 describes a similar example in which
to approximately 40% of the extinctions recorded since 1750 conservation biologists used DNA analyses to compare harvested samples of
and costing billions of dollars each year in damage and con- whale meat with a reference DNA database. How are these examples similar,
trol efforts. There are more than 50,000 introduced species and how are they different? What limitations might there be to using such
in the United States alone. forensic methods in other suspected cases of poaching?

Overharvesting overfishing. Demands from an increasing human population
for protein-rich food, coupled with new harvesting technolo-
The term overharvesting refers generally to the harvesting of gies, such as long-line fishing and modern trawlers, have
wild organisms at rates exceeding the ability of their popula- reduced these fish populations to levels that cannot sustain
tions to rebound. Species with restricted habitats, such as further exploitation. Until the past few decades, the Atlantic
those that inhabit small islands, are particularly vulnerable bluefin tuna was considered a sport fish of little commercial
to overharvesting. One such species was the great auk, a large, value—just a few cents per pound for use in cat food. In the
flightless seabird found on islands in the North Atlantic. By 1980s, however, wholesalers began airfreighting fresh, iced
the 1840s, humans had hunted the great auk to extinction bluefin to Japan for sushi and sashimi. In that market, the
to satisfy demand for its feathers, eggs, and meat. fish now brings up to $100 per pound (Figure 56.10). With
increased harvesting spurred by such high prices, it took just
Also susceptible to overharvesting are large organisms ten years to reduce the western Atlantic bluefin population
with low reproductive rates, such as elephants, whales, and to less than 20% of its 1980 size.
rhinoceroses. The decline of Earth’s largest terrestrial animals,
the African elephants, is a classic example of the impact of Figure 56.10  Overharvesting. Atlantic bluefin tuna are
overhunting. Largely because of the trade in ivory, elephant auctioned in a Japanese fish market.
populations have been declining in most of Africa for the last
50 years. An international ban on the sale of new ivory resulted
in increased poaching (illegal hunting), so the ban had little
effect in much of central and eastern Africa. Only in South
Africa, where once-decimated herds have been well protected
for nearly a century, have elephant populations been stable
or increasing (see Figure 53.9).

Conservation biologists are increasingly using the tools
of molecular genetics to track the origins of tissues har-
vested from endangered species. For example, researchers
have used DNA isolated from samples of elephant dung to
construct a DNA reference map for the African elephant
(Loxodonta africana). By comparing this reference map with
DNA isolated from ivory harvested legally or by poachers,
they can determine to within a few hundred kilometers
where the elephants were killed (Figure 56.9). Such work in
Zambia suggested that poaching rates were 30 times higher
than previously estimated, a finding that has stimulated
improved anti-poaching efforts by the Zambian govern-
ment. Similarly, biologists using phylogenetic analyses of
mitochondrial DNA (mtDNA) showed that some whale meat
sold in Japanese fish markets came from illegally harvested
species, including fin and humpback whales, which are
endangered (see Figure 26.6).

Many commercially important fish populations, once
thought to be inexhaustible, have been decimated by

chapter 56  Conservation Biology and Global Change 1263

pHGlobal Change ecologists estimate that it will take decades for aquatic eco-
systems to recover. Meanwhile, emissions of nitrogen oxides
The fourth threat to biodiversity, global change, alters the are increasing in the United States, and emissions of sulfur
fabric of Earth’s ecosystems at regional to global scales. Global dioxide and acid precipitation continue to damage forests in
change includes alterations in climate, atmospheric chemistry, central and eastern Europe.
and broad ecological systems that reduce the capacity of Earth
to sustain life. We’ll explore the importance of global change for Earth’s
biodiversity in more detail in Concept 56.4, where we examine
One of the first types of global change to cause concern such factors as climate change and ozone depletion. Next, we’ll
was acid precipitation, which is rain, snow, sleet, or fog with a take a closer look at how scientists seek to protect populations
pH less than 5.2. The burning of wood and fossil fuels releases and species under threat.
oxides of sulfur and nitrogen that react with water in air, form-
ing sulfuric and nitric acids. The acids eventually fall to Earth’s Concept Check 56.1
surface, where they cause chemical reactions that decrease
nutrient supplies and increase concentrations of toxic metals. 1. Explain why it is too narrow to define the biodiversity
These changes to the soil and water harm some terrestrial and crisis as simply a loss of species.
aquatic organisms.
2. Identify the four main threats to biodiversity and explain
In the 1960s, ecologists determined that lake-dwelling how each damages diversity.
organisms in eastern Canada were dying because of air pol-
lution from factories in the Midwestern United States. Newly 3. WHAT IF? Imagine two populations of a fish species,
hatched lake trout, for instance, die when the pH drops below one in the Mediterranean Sea and one in the Caribbean
5.4. Lakes and streams in southern Norway and Sweden were Sea. Now imagine two scenarios: (1) The populations
losing fish because of pollution generated in Great Britain and breed separately, and (2) adults of both populations
central Europe. By 1980, the pH of precipitation in large areas migrate yearly to the North Atlantic to interbreed. Which
of North America and Europe averaged 4.0–4.5 and sometimes scenario would result in a greater loss of genetic diversity
dropped as low as 3.0. (To review pH, see Concept 3.3.) if the Mediterranean population were harvested
to extinction? Explain your answer.
Environmental regulations and new technologies have For suggested answers, see Appendix A.
enabled many countries to reduce sulfur dioxide emissions in
recent decades. In the United States, sulfur dioxide emissions Concept  56.2
decreased more than 75% between 1990 and 2013, gradually
reducing the acidity of precipitation (Figure 56.11). However, Population conservation focuses
on population size, genetic diversity,
Figure 56.11  Changes in the pH of precipitation at the and critical habitat
Hubbard Brook Experimental Forest, New Hampshire.
Biologists who work on conservation at the population and
4.9 species levels use two main approaches. One approach focuses
on populations that are small and hence often vulnerable. The
4.8 other emphasizes populations that are declining rapidly, even
if they are not yet small.
4.7
Small-Population Approach
4.6
Small populations are particularly vulnerable to overhar-
4.5 vesting, habitat loss, and the other threats to biodiversity
that you read about in Concept 56.1. After such factors have
4.4 reduced a population’s size to a small number of individuals,
the small size itself can push the population to extinction.
4.3 The small-population approach emphasizes the various pro-
cesses that cause extinctions once population sizes have been
4.2 greatly reduced.

4.1 The Extinction Vortex: Evolutionary Implications
of Small Population Size
4.0
Evolution A small population is vulnerable to inbreeding
1960 ‘65 ‘70 ‘75 ‘80 ‘85 ‘90 ‘95 2000 ‘05 ‘10 ‘15 and genetic drift, which can draw the population down an
Year extinction vortex toward smaller and smaller population

MAKE CONNECTIONS Describe the relationship between pH and
acidity. (See Concept 3.3.) Overall, is the precipitation in this forest becoming
more acidic or less acidic?

1264 unit eight  Ecology

Figure 56.12  Processes driving an extinction vortex. Figure 56.13

Small Inbreeding, Inquiry  What caused the drastic decline of the
population genetic Illinois greater prairie chicken population?
drift
Experiment  Researchers had observed that the population col-
Lower reproduction, lapse of the greater prairie chicken was mirrored in a reduction in
higher mortality fertility, as measured by the hatching rate of eggs. Comparison of
DNA samples from the Jasper County, Illinois, population with DNA
Lower individual Loss of from feathers in museum specimens showed that genetic variation
fitness and genetic had declined in the study population (see Figure 23.11). In 1992,
variability Ronald Westemeier and colleagues began translocating prairie
population adaptability chickens from neighboring states in an attempt to increase
genetic variation.
Results  After translocation (black arrow), the viability of eggs rapidly
increased, and the population rebounded.

Smaller 200
population

size until no individuals survive (Figure 56.12). A key factor Number of male birds 150
driving the extinction vortex is the loss of genetic variation
that can enable evolutionary responses to environmental 100
change, such as the appearance of new strains of pathogens. Translocation
Both inbreeding and genetic drift can cause a loss of genetic
variation (see Concept 23.3), and their effects become more 50
harmful as a population shrinks. Inbreeding often reduces
fitness because offspring are more likely to be homozygous 0 1975 1980 1985 1990 1995
for harmful recessive traits. 1970

Not all small populations are doomed by low genetic diver- (a) Population dynamics Year
sity, and low genetic variability does not automatically lead
to permanently small populations. For instance, overhunting 100
of northern elephant seals in the 1890s reduced the species to
only 20 individuals—clearly a bottleneck with reduced genetic Eggs hatched (%) 90
variation. Since that time, however, the northern elephant
seal populations have rebounded to about 150,000 individuals 80
today, though their genetic variation remains relatively low.
70
Case Study: The Greater Prairie Chicken
and the Extinction Vortex 60

When Europeans arrived in North America, the greater prai- 50
rie chicken (Tympanuchus cupido) was common from New
England to Virginia and across the western prairies of the 40
continent. Land cultivation for agriculture fragmented the
populations of this species, and its abundance decreased 30 1975 1980 1985 1990 1995
rapidly (see Figure 23.11). Illinois had millions of greater 1970
prairie chickens in the 19th century but fewer than 50 by
1993. Researchers found that the decline in the Illinois popu- Year
lation was associated with reduced genetic variation and a
decrease in fertility. As a test of the extinction vortex hypoth- (b) Hatching rate. Bar height represents the average rate for
esis, scientists increased genetic variation by importing 271 the years spanned by the bar.
birds from larger populations elsewhere (Figure 56.13). The
Illinois population rebounded, indicating that it had been Conclusion  Reduced genetic variation had started the Jasper
on its way to extinction until rescued by the transfusion of County population of prairie chickens down the extinction vortex.
genetic variation.
Data from  R. L. Westemeier et al., Tracking the long-term decline and recovery of
an isolated population, Science 282:1695–1698 (1998). © 1998 by AAAS. Reprinted
with permission.

Inquiry in Action  Read and analyze the original paper in Inquiry
in Action: Interpreting Scientific Papers.

WHAT IF? Given the success of using transplanted birds as a tool for
increasing the percentage of hatched eggs in Illinois, would you support
transplanting additional birds to Illinois? Why or why not?

chapter 56  Conservation Biology and Global Change 1265

Minimum Viable Population Size active individuals. The conservation goal of sustaining effective
population size (Ne) above MVP stems from the concern that
How small does a population have to be before it starts down populations retain enough genetic diversity to adapt as their
an extinction vortex? The answer depends on the type of environment changes.
organism and other factors. Large predators that feed high on
the food chain usually require extensive individual ranges, The MVP of a population is often used in population
resulting in low population densities. Such species may be rare viability analysis. The objective of this analysis is to predict
yet of little concern to conservation biologists. All populations, a population’s chances for survival, usually expressed as a
however, require some minimum size to remain viable. specific probability of survival, such as a 95% chance, over
a particular time interval, perhaps 100 years. Such model-
The minimal population size at which a species is able to ing approaches allow conservation biologists to explore the
sustain its numbers is known as the minimum viable potential consequences of alternative management plans.
population (MVP). MVP is usually estimated for a given
species using computer models that integrate many factors. Case Study: Analysis of Grizzly Bear
The calculation may include, for instance, an estimate of how Populations
many individuals in a small population are likely to be killed
by a natural catastrophe such as a storm. Once in the extinc- One of the first population viability analyses was conducted
tion vortex, two or three consecutive years of bad weather in 1978 by Mark Shaffer as part of a long-term study of grizzly
could finish off a population that is already below its MVP. bears in Yellowstone National Park and its surrounding areas
(Figure 56.14). A threatened species in the United States, the
Effective Population Size grizzly bear (Ursus arctos horribilis) is currently found in only
4 of the 48 contiguous states. Its populations in those states
Genetic variation is a key issue in the small-population have been drastically reduced and fragmented. In 1800, an esti-
mated 100,000 grizzlies ranged over about 500 million hectares
approach. The total size of a population may be misleading of habitat, while today only 1,000 individuals in six relatively
isolated populations range over less than 5 million hectares.
because only certain members of the population breed suc-
Shaffer attempted to determine viable sizes for the
cessfully and pass their alleles on to offspring. Therefore, a Yellowstone grizzly population. Using life history data
obtained for individual Yellowstone bears over a 12-year
meaningful estimate of MVP requires the researcher to deter- period, he simulated the effects of environmental factors
mine the effective population size, which is based on the on survival and reproduction. His models predicted that,
given a suitable habitat, a Yellowstone grizzly bear popula-
breeding potential of the population. tion of 70–90 individuals would have about a 95% chance of
surviving for 100 years. A slightly larger population of only
The following formula illustrates one way to estimate the 100 bears would have a 95% chance of surviving for twice as
long, about 200 years.
effective population size, abbreviated Ne:
Figure 56.14  Long-term monitoring of a grizzly bear
Ne = 4NfNm population. The ecologist is fitting this tranquilized bear with a radio
Nf + Nm collar so that the bear’s movements can be compared with those of
other grizzlies in the Yellowstone National Park population.
where Nf and Nm are, respectively, the number of females and
the number of males that successfully breed. If we apply this

formula to an idealized population whose total size is 1,000

individuals, Ne will also be 1,000 if every individual breeds
and the sex ratio is 500 females to 500 males. In this case, Ne =
(4 * 500 * 500)/(500 + 500) = 1,000. Any deviation from
these conditions (not all individuals breed or there is not a 1:1

sex ratio) reduces Ne. For instance, if the total population size
is 1,000 but only 400 females and 400 males breed, then Ne =
(4 * 400 * 400)/(400 + 400) = 800, or 80% of the total popu-
lation size. Numerous factors can influence Ne. Alternative for-
mulas for estimating Ne take into account factors such as age at
maturation, genetic relatedness among population members,

the effects of gene flow, and population fluctuations.

In actual study populations, Ne is always some fraction of
the total population. Thus, simply determining the total num-

ber of individuals in a small population does not necessarily

provide a good measure of whether the population is large

enough to avoid extinction. Whenever possible, conserva-

tion programs attempt to sustain total population sizes that

include at least the minimum viable number of reproductively

1266 unit eight  Ecology

How does the actual size of the Yellowstone grizzly popula- human activities and natural events. The following case study
tion compare with Shaffer’s predicted MVP? A current estimate illustrates how the declining-population approach has been
puts the total grizzly bear population in the greater Yellowstone applied to the conservation of an endangered species.
ecosystem at about 400 individuals. The relationship of this
estimate to the effective population size (Ne) depends on several Case Study: Decline of the Red-Cockaded
factors. Usually, only a few dominant males breed, and it may Woodpecker
be difficult for them to locate females, since individuals inhabit
such large areas. Moreover, females may reproduce only when The red-cockaded woodpecker (Picoides borealis) is found
there is abundant food. As a result, Ne is only about 25% of the only in the southeastern United States. It requires mature
total population size, or about 100 bears. pine forests, preferably ones dominated by the longleaf pine,
for its habitat. A critical habitat factor for the red-cockaded
Because small populations tend to lose genetic variation over woodpecker is that the undergrowth of plants around the
time, researchers have used proteins, mitochondrial DNA, and pine trunks must be low (Figure 56.15a). Breeding birds
short tandem repeats (see Concept 21.4) to assess genetic vari- tend to abandon nests when vegetation among the pines is
ability in the Yellowstone grizzly bear population. All results to thick and higher than about 4.5 m (Figure 56.15b); the birds
date indicate that the Yellowstone population has less genetic
variability than other grizzly bear populations in North America. Figure 56.15  A habitat requirement of the red-cockaded
woodpecker.
How might conservation biologists increase the effective
size and genetic variation of the Yellowstone grizzly bear (a) Forests that can sustain red-cockaded woodpeckers have low
population? Migration between isolated populations of griz- undergrowth.
zlies could increase both effective and total population sizes.
Computer models predict that introducing only two unrelated (b) Forests that cannot sustain red-cockaded woodpeckers have high,
bears each decade into a population of 100 individuals would dense undergrowth that interferes with the woodpeckers‘ access
reduce the loss of genetic variation by about half. For the griz- to feeding grounds.
zly bear, and probably for many other species with small popu-
lations, finding ways to promote dispersal among populations ? How is habitat disturbance absolutely necessary for the long-term
may be one of the most urgent conservation needs. survival of the woodpecker?

This case study and that of the greater prairie chicken
bridge small-population models and practical applications
in conservation. Next, we look at an alternative approach
to understanding the biology of extinction.

Declining-Population Approach

The declining-population approach focuses on threatened
and endangered populations that show a downward trend,
even if the population is far above its minimum viable popu-
lation. The distinction between a declining population,
which may not be small, and a small population, which may
not be declining, is less important than the different priorities
of the two approaches. While the small-population approach
emphasizes smallness itself as an ultimate cause of a popula-
tion’s extinction, the declining-population approach empha-
sizes the environmental factors that caused a population
decline in the first place. If, for instance, an area is deforested,
then species that depend on trees will decline in abundance,
whether or not they retain genetic variation.

The declining-population approach requires that research-
ers carefully evaluate the causes of a decline before taking
steps to correct it. A key step in this process is to study the
natural history of a declining species, including a review of
the scientific literature, to determine the species’ environ-
mental needs. This information is then used to develop and
test hypotheses of possible causes of the decline, including

chapter 56  Conservation Biology and Global Change 1267

appear to need a clear flight path between their home trees per hectare but can grow beneath trees that support large
and the neighboring feeding grounds. Periodic fires have numbers of songbirds?
historically swept through longleaf pine forests, keeping the
undergrowth low. Another important consideration is the ecological role of
a species. Because we cannot save every endangered species,
In addition, although most woodpeckers nest in dead trees, we must determine which species are most important for con-
the red-cockaded woodpecker drills its nest holes in mature, serving biodiversity as a whole. Identifying keystone species
living pine trees. It also drills small holes around the entrance and finding ways to sustain their populations can be central
to its nest cavity, which causes resin from the tree to ooze to maintaining communities and ecosystems. In most situa-
down the trunk. The resin seems to repel predators, such as tions, conservation biologists must also look beyond single
corn snakes, that eat bird eggs and nestlings. species and consider the whole community and ecosystem
as an important unit of biodiversity.
One factor leading to decline of the red-cockaded wood-
pecker has been the destruction or fragmentation of suitable Concept Check 56.2
habitats by logging and agriculture. By recognizing key habi-
tat factors, protecting some longleaf pine forests, and using 1. How does the reduced genetic diversity of small popula-
controlled fires to reduce forest undergrowth, conservation tions make them more vulnerable to extinction?
managers have helped restore habitat that can support
viable populations. 2. If there were 100 greater prairie chickens in a popula-
tion, and 30 females and 10 males bred, what would
Sometimes conservation managers also help species be the effective population size (Ne)?
colonize restored habitats. Because red-cockaded woodpeck-
ers take months to excavate nesting cavities, researchers 3. WHAT IF? In 2005, at least ten grizzly bears in the
performed an experiment to see whether providing cavi- greater Yellowstone ecosystem were killed through
ties for the birds would make them more likely to use a site. contact with people. Most of these deaths resulted from
The researchers constructed cavities in pine trees at 20 sites. three things: collisions with automobiles, hunters (of
The results were dramatic. Cavities in 18 of the 20 sites were other animals) shooting when charged by a female griz-
colonized by red-cockaded woodpeckers, and new breeding zly bear with cubs nearby, and conservation managers
groups formed only in those sites. Based on this experiment, killing bears that attacked livestock repeatedly. If you
conservationists initiated a habitat maintenance program were a conservation manager, what steps might you take
that included controlled burning and excavation of new to minimize such encounters in Yellowstone?
nesting cavities, enabling this endangered species to begin For suggested answers, see Appendix A.
to recover.
Concept  56.3
Weighing Conflicting Demands
Landscape and regional conservation
Determining population numbers and habitat needs is only help sustain biodiversity
part of a strategy to save species. Scientists also need to
weigh a species’ needs against other conflicting demands. Although conservation efforts have historically focused on
Conservation biology often highlights the relationship saving individual species, efforts today often seek to sustain
between science, technology, and society. For example, an the biodiversity of entire communities, ecosystems, and land-
ongoing, sometimes bitter debate in the western United scapes. Such a broad view requires applying not just ecologi-
States pits habitat preservation for wolf, grizzly bear, and cal principles, but aspects of human population dynamics
bull trout populations against job opportunities in the and economics as well.
grazing and resource extraction industries. Programs that
restocked wolves in Yellowstone National Park remain con- Landscape Structure and Biodiversity
troversial for people concerned about human safety and for
many ranchers concerned with potential loss of livestock The biodiversity of a given landscape is heavily influenced by
outside the park. its physical features, or structure. Understanding landscape
structure is critically important in conservation because
Large, high-profile vertebrates are not always the focal many species use more than one kind of ecosystem, and
point in such conflicts, but habitat use is almost always the many live on the borders between ecosystems.
issue. Should work proceed on a new highway bridge if it
destroys the only remaining habitat of a species of freshwater Fragmentation and Edges
mussel? If you were the owner of a coffee plantation growing
varieties that thrive in bright sunlight, would you be willing The boundaries, or edges, between ecosystems—such as
to change to shade-tolerant varieties that produce less coffee between a lake and the surrounding forest or between crop-
land and suburban housing tracts—are defining features of
landscapes (Figure 56.16). An edge has its own set of physical

1268 unit eight  Ecology

Figure 56.16  Natural edges between ecosystems in Siberia. Figure 56.17  Amazon rain forest fragments created as
part of the Biological Dynamics of Forest Fragments Project.

VISUAL SKILLS What edges between ecosystems do you observe organisms ranging from bryophytes to beetles to birds. They
in this photo? have consistently found that species adapted to forest interi-
ors show the greatest declines when patches are the smallest,
conditions, which differ from those on either side of it. The suggesting that landscapes dominated by small fragments
soil surface of an edge between a forest patch and a burned will support fewer species.
area receives more sunlight and is usually hotter and drier
than the forest interior, but it is cooler and wetter than the Corridors That Connect Habitat Fragments
soil surface in the burned area.
In fragmented habitats, the presence of a movement
Some organisms thrive in edge communities because corridor, a narrow strip or series of small clumps of
they gain resources from both adjacent areas. The ruffed habitat connecting otherwise isolated patches, can be
grouse (Bonasa umbellus) is a bird that needs forest habitat extremely important for conserving biodiversity. Riparian
for nesting, winter food, and shelter, but it also needs forest habitats often serve as corridors, and in some nations, gov-
openings with dense shrubs and herbs for summer food. ernment policy prohibits altering these habitats. In areas
of heavy human use, artificial corridors are sometimes
Ecosystems in which edges arise from human alterations constructed. Bridges or tunnels, for instance, can reduce
often have reduced biodiversity and a preponderance of edge- the number of animals killed trying to cross highways
adapted species. For example, white-tailed deer (Odocoileus (Figure 56.18).
virginianus) thrive in edge habitats, where they can browse on
woody shrubs; deer populations often expand when forests Figure 56.18  An artificial corridor. This highway overpass
are logged and more edges are generated. The brown-headed in the Netherlands helps animals cross a human-created barrier.
cowbird (Molothrus ater) is an edge-adapted species that lays
its eggs in the nests of other birds, often migratory songbirds.
Cowbirds need forests, where they can parasitize the nests of
other birds, and open fields, where they forage on seeds and
insects. Consequently, their populations are growing where
forests are being cut and fragmented, creating more edge hab-
itat and open land. Increasing cowbird parasitism and habitat
loss are correlated with declining populations of several of the
cowbird’s host species.

The influence of fragmentation on the structure of com-
munities has been explored since 1979 in the long-term
Biological Dynamics of Forest Fragments Project. Located in
the heart of the Amazon River basin, the study area consists
of isolated fragments of tropical rain forest separated from
surrounding continuous forest by distances of 80–1,000 m
(Figure 56.17). Numerous researchers working on this project
have clearly documented the effects of this fragmentation on

chapter 56  Conservation Biology and Global Change 1269

Movement corridors can also promote dispersal and birds), and mammals. Aquatic ecosystems also have hot spots,
reduce inbreeding in declining populations. Corridors have such as coral reefs and certain river systems.
been shown to increase the exchange of individuals among
populations of many organisms, including butterflies, voles, Biodiversity hot spots are good choices for nature reserves,
and aquatic plants. Corridors are especially important to but identifying them is not always simple. One problem is
species that migrate between different habitats seasonally. that a hot spot for one taxonomic group, such as butterflies,
However, a corridor can also be harmful—for example, by may not be a hot spot for some other taxonomic group, such
allowing the spread of disease. In a 2003 study, a scientist at as birds. Designating an area as a biodiversity hot spot is often
the University of Zaragoza, Spain, showed that habitat corri- biased toward saving vertebrates and plants, with less atten-
dors facilitate the movement of disease-carrying ticks among tion paid to invertebrates and microorganisms. Some biolo-
forest patches in northern Spain. All the effects of corridors gists are also concerned that the hot-spot strategy places too
are not yet understood, and their impact is an area of active much emphasis on such a small fraction of Earth’s surface.
research in conservation biology.
Global change makes the task of preserving hot spots
Establishing Protected Areas even more challenging because the conditions that favor a
particular community may not be found in the same loca-
Currently, governments have set aside about 7% of the world’s tion in the future. The biodiversity hot spot in the south-
land in various forms of reserves. Choosing where to place west corner of Australia (see Figure 56.19) holds thousands
nature reserves and how to design them poses many challenges. of species of endemic plants and numerous endemic verte-
Should the reserve be managed to minimize the risks of fire and brates. Researchers recently concluded that between 5% and
predation to a threatened species? Or should the reserve be left 25% of the plant species they examined may become extinct
as natural as possible, with such processes as fires ignited by by 2080 because the plants will be unable to tolerate the
lightning allowed to play out on their own? This is just one of increased dryness predicted for this region.
the debates that arise among people who share an interest in
the health of national parks and other protected areas. Philosophy of Nature Reserves

Preserving Biodiversity Hot Spots Nature reserves are protected “islands” of biodiversity in
a sea of habitat altered or degraded by human activity. An
In deciding which areas are of highest conservation prior- earlier policy—that protected areas should be set aside to
ity, biologists often focus on hot spots of biodiversity. A remain unchanged forever—was based on the concept that
b­ iodiversity hot spot is a relatively small area with numer- ecosystems are balanced, self-regulating units. However,
ous endemic species (species found nowhere else in the world) disturbance is common in all ecosystems (see Concept 54.3).
and a large number of endangered and threatened species Management policies that ignore disturbances or attempt to
(Figure 56.19). Nearly 30% of all bird species can be found prevent them have generally failed. For instance, setting aside
in hot spots that make up only about 2% of Earth’s land area. an area of a fire-dependent community, such as a portion of a
Together, the “hottest” of the terrestrial biodiversity hot spots tallgrass prairie, chaparral, or dry pine forest, with the inten-
total less than 1.5% of Earth’s land but are home to more than tion of saving it is unrealistic if periodic burning is excluded.
a third of all species of plants, amphibians, reptiles (including Without the dominant disturbance, the fire-adapted species
are usually outcompeted and biodiversity is reduced.
Figure 56.19  Earth’s terrestrial and marine
biodiversity hot spots.

Equator

Key Marine hot spot
Terrestrial hot spot

1270 unit eight  Ecology

An important conservation question is whether to cre- Figure 56.20  Protected areas in Costa Rica.
ate numerous small reserves or fewer large reserves. Small,
unconnected reserves may slow the spread of disease between Nicaragua CARIBBEAN SEA
populations. One argument for large reserves is that large,
far-ranging animals with low-density populations, such as Costa
the grizzly bear, require extensive habitats. Large reserves also Rica
have proportionately smaller perimeters than small reserves
and are therefore less affected by edges. Protected land Panama
Protected ocean
As conservation biologists have learned more about the
requirements for achieving minimum viable populations for PACIFIC OCEAN
endangered species, they have realized that most national
parks and other reserves are far too small. The area needed (a) Boundaries of the Conservation Areas are indicated by black outlines.
for the long-term survival of the Yellowstone grizzly bear
population, for instance, is more than 11 times the area (b) Tourists marvel at the diversity of life in one of Costa Rica’s
of Yellowstone National Park. Areas of private and public protected areas.
land surrounding reserves will likely have to contribute to
biodiversity conservation. less common than reserves on land. Many fish populations
around the world have collapsed as increasingly sophisticated
Zoned Reserves equipment puts nearly all potential fishing grounds within
human reach. In response, scientists at the University of York,
Several nations have adopted a zoned reserve approach to England, have proposed establishing marine reserves around
landscape management. A zoned reserve is an extensive the world that would be off-limits to fishing. They present
region that includes areas relatively undisturbed by humans strong evidence that a patchwork of marine reserves can serve
surrounded by areas that have been changed by human activ- as a means of both increasing fish populations within the
ity and are used for economic gain. The key challenge of the reserves and improving fishing success in nearby areas. Their
zoned reserve approach is to develop a social and economic proposed system is a modern application of a centuries-old
climate in the surrounding lands that is compatible with practice in the Fiji Islands in which some areas have histori-
the long-term viability of the protected core. These sur- cally remained closed to fishing—a traditional example of the
rounding areas continue to support human activities, but zoned reserve concept.
regulations prevent the types of extensive alterations likely
to harm the protected area. As a result, the surrounding habi- The United States adopted such a system in creating a set
tats serve as buffer zones against further intrusion into the of 13 national marine sanctuaries, including the Florida Keys
undisturbed area. National Marine Sanctuary, which was established in 1990

The Central American nation of Costa Rica has become
a world leader in establishing zoned reserves. An agreement
initiated in 1987 reduced Costa Rica’s international debt
in return for land preservation there. The country is now
divided into 11 Conservation Areas, which include national
parks and other protected areas, both on land and in the
ocean (Figure 56.20). Costa Rica is making progress toward
managing its zoned reserves, and the buffer zones provide a
steady, lasting supply of forest products, water, and hydro-
electric power while also supporting sustainable agriculture
and tourism, both of which employ local people.

Costa Rica relies on its zoned reserve system to maintain
at least 80% of its native species, but the system is not with-
out problems. A 2003 analysis of land cover change between
1960 and 1997 showed negligible deforestation within Costa
Rica’s national parks and a gain in forest cover in the 1-km
buffer around the parks. However, significant losses in forest
cover were discovered in the 10-km buffer zones around all
national parks, threatening to turn the parks into isolated
habitat islands.

Although marine ecosystems have also been heavily
affected by human exploitation, reserves in the ocean are far

chapter 56  Conservation Biology and Global Change 1271

Figure 56.21  A diver measuring coral in the Florida Figure 56.22  Volunteers working to remove invasive
species along the urban Guichon Creek.
Keys National

Marine Sanctuary. GULF OF MEXICO FLORIDA

Florida Keys National
Marine Sanctuary

50 km

(Figure 56.21). Populations of marine organisms, includ- planted native trees and shrubs along the creek (Figure 56.22).
ing fishes and lobsters, recovered quickly after harvests were Their efforts returned the water flow and the communities of
banned in the 9,500-km2 reserve. Larger and more abundant invertebrates and fish in the stream much closer to what they
fish now produce larvae that help repopulate reefs and improve had been 50 years before the stream became degraded. A few
fishing outside the sanctuary. The increased marine life within years ago, ecologists successfully reestablished cutthroat trout
the sanctuary also makes it a favorite for recreational divers, in the stream. The trout are now thriving.
increasing the economic value of this zoned reserve.
As cities continue to expand into the landscapes around
Urban Ecology them, understanding the ecological effects of this expansion
will only increase in importance. Research on and conserva-
The zoned reserves that you just read about combine habi- tion of urban habitats will continue to grow.
tats that are relatively undisturbed by human activity with
those that are used extensively by people for economic gain. Concept Check 56.3
Increasingly, ecologists are looking at species preservation
even in the context of cities. The field of urban ecology 1. What is a biodiversity hot spot?
examines organisms and their environment in urban settings. 2. How do zoned reserves provide economic incentives for

For the first time in history, more than half of the people long-term conservation of protected areas?
on Earth live in cities. By the year 2030, 5 billion people are 3. WHAT IF? Suppose a developer proposes to clear-cut
expected to be living in urban environments. As cities expand
in number and size, protected areas that were once outside a forest that serves as a corridor between two parks. To
city boundaries become incorporated into urban landscapes. compensate, the developer also proposes to add the same
Ecologists are now studying cities as ecological laboratories, area of forest to one of the parks. As a professional ecolo-
seeking to balance species preservation and other ecological gist, how might you argue for retaining the corridor?
needs with the needs of people.
For suggested answers, see Appendix A.
One critical area of research centers on urban streams,
including the quality and flow of their water and the organ- Concept  56.4
isms living in them. Urban streams tend to rise and fall more
quickly after rain than natural streams. This rapid change in Earth is changing rapidly as a result
water level occurs because of the concrete and other impervi- of human actions
ous surfaces in cities as well as the drainage systems that route
water out of cities as quickly as possible to avoid flooding. As we’ve discussed, landscape and regional conservation help
Urban streams also tend to have higher concentrations of protect habitats and preserve species. However, environmen-
nutrients and contaminants and are often straightened or tal changes that result from human activities are creating
even channeled underground. new challenges. As a consequence of human-caused climate
change, for example, the place where a vulnerable species is
Near Vancouver, British Columbia, ecologists and volun- found today may not be the same place that is needed for pres-
teers have worked to restore a degraded urban stream, Guichon ervation in the future. What would happen if many habitats
Creek. They stabilized its banks, removed invasive plants, and on Earth changed so quickly that the locations of preserves
today were unsuitable for their species in 10, 50, or 100 years?
1272 unit eight  Ecology Such a scenario is increasingly possible.

The rest of this section describes four types of environ- nitrates from the soil. As shown in Figure 55.15, without plants
mental change that humans are bringing about: nutrient to absorb them, nitrates are often leached from the ecosystem.
enrichment, toxin accumulation, climate change, and ozone
depletion. The impacts of these and other changes are evident Recent studies indicate that human activities have more
not just in human-dominated ecosystems, such as cities and than doubled Earth’s supply of fixed nitrogen available to pri-
farms, but also in the most remote ecosystems on Earth. mary producers. Industrial fertilizers provide the largest addi-
tional nitrogen source. Fossil fuel combustion also releases
Nutrient Enrichment nitrogen oxides, which enter the atmosphere and dissolve
in rainwater; the nitrogen ultimately enters ecosystems as
Human activity often removes nutrients from one part of the nitrate. Increased cultivation of legumes, with their nitrogen-
biosphere and adds them to another. Someone eating broc- fixing symbionts, is a third way in which humans increase
coli in Washington, DC, consumes nutrients that only days the amount of fixed nitrogen in the soil.
before were in the soil in California; a short time later, some
of these nutrients will be in the Potomac River, having passed A problem arises when the nutrient level in an ecosystem
through the person’s digestive system and a local sewage treat- exceeds the critical load, the amount of added nutrient,
ment facility. Likewise, nutrients in farm soil may run off into usually nitrogen or phosphorus, that can be absorbed by
streams and lakes, depleting nutrients in one area, increasing plants without damaging ecosystem integrity. For example,
them in another, and altering chemical cycles in both. nitrogenous minerals in the soil that exceed the critical load
eventually leach into groundwater or run off into freshwa-
Farming illustrates how human activities can lead to nutrient ter and marine ecosystems, contaminating water supplies
enrichment. After vegetation is cleared from an area, the existing and killing fish. Nitrate concentrations in groundwater are
reserve of nutrients in the soil is depleted because many of these increasing in most agricultural regions, sometimes reaching
nutrients are exported from the area in crop biomass. The “free” levels that are unsafe for drinking.
period for crop production—when there is no need to replenish
nutrients by adding fertilizer to the soil—varies greatly. When Many rivers contaminated with nitrates and ammonium
some of the early North American prairie lands were first tilled, from agricultural runoff and sewage drain into the Atlantic
good crops could be produced for decades because the large store Ocean, with the highest inputs coming from northern Europe
of organic materials in the soil continued to decompose and and the central United States. The Mississippi River carries
provide nutrients. By contrast, some cleared land in the tropics nitrogen pollution to the Gulf of Mexico, fueling a phyto-
can be farmed for only one or two years because so little of the plankton bloom each summer. When the phytoplankton die,
ecosystems’ nutrient load is contained in the soil. Despite such their decomposition by oxygen-using organisms creates an
variations, in any area under intensive agriculture, the natural extensive “dead zone” of low oxygen levels along the coast
store of nutrients eventually becomes exhausted. (Figure 56.24). When this occurs, fish and other marine ani-
mals disappear from some of the most economically important
Consider nitrogen, the main nutrient lost through agricul- waters in the United States. To reduce the size of the dead zone,
ture (see Figure 55.14). Plowing mixes the soil and speeds up farmers have begun using fertilizers more efficiently, and man-
decomposition of organic matter, releasing nitrogen that is agers are restoring wetlands in the Mississippi watershed.
then removed when crops are harvested. Fertilizers contain-
ing nitrates and other forms of nitrogen that plants can absorb Nutrient runoff can also lead to the eutrophication of lakes
are used to replace the nitrogen that is lost (Figure 56.23). (see Concept 55.2). The bloom and subsequent die-off of
However, after crops are harvested, few plants remain to take up algae and cyanobacteria and the ensuing depletion of oxygen
are similar to what occurs in a marine dead zone. Such condi-
Figure 56.23  Fertilization of a corn (maize) crop. To replace tions threaten the survival of many organisms. For example,
the nutrients removed in crops, farmers must apply fertilizers—either eutrophication of Lake Erie coupled with overfishing wiped
organic, such as manure or mulch, or synthetic, as shown here. out commercially important fishes such as blue pike, whitefish,

Figure 56.24 
A phytoplankton
bloom arising from
nitrogen pollution
in the Mississippi
basin that leads
to a dead zone. In
this satellite image
from 2004, red and
orange represent high
concentrations of
phytoplankton in the
Gulf of Mexico.

chapter 56  Conservation Biology and Global Change 1273

and lake trout by the 1960s. Since then, tighter regulations on Concentration of PCBs Herring Lake trout
the dumping of sewage into the lake have enabled some fish gull eggs 4.83 ppm
populations to rebound, but many native species of fish and 124 ppm
invertebrates have not recovered.
Smelt
Animation: Water Pollution from Nitrates 1.04 ppm

Toxins in the Environment Zooplankton Phytoplankton
0.123 ppm 0.025 ppm
Humans release an immense variety of toxic chemicals, includ-
ing thousands of synthetic compounds previously unknown Figure 56.25  Biological magnification of PCBs in a Great
in nature, with little regard for the ecological consequences. Lakes food web. (ppm = parts per million)
Organisms acquire toxic substances from the environment
along with nutrients and water. Some of the poisons are ? Calculate how much the PCB concentration increased at each step in the
metabolized or excreted, but others accumulate in specific food web.
tissues, often fat. One of the reasons accumulated toxins are
particularly harmful is that they become more concentrated In much of the tropics, DDT is still used to control the mos-
in successive trophic levels of a food web. This phenomenon, quitoes that spread malaria and other diseases. Societies there
called biological magnification, occurs because the bio- face a trade-off between saving human lives and protecting
mass at any given trophic level is produced from a much larger other species. The best approach seems to be to apply DDT spar-
biomass ingested from the level below (see Concept 55.3). ingly and to couple its use with mosquito netting and other
Thus, top-level carnivores tend to be most severely affected by low-technology solutions. The complicated history of DDT
toxic compounds in the environment. illustrates the importance of understanding the ecological con-
nections between diseases and communities (see Concept 54.5).
Chlorinated hydrocarbons are a class of industrially
synthesized compounds that have demonstrated biological Pharmaceuticals make up another group of toxins in the
magnification. Chlorinated hydrocarbons include the indus- environment, one that is a growing concern among ecolo-
trial chemicals called PCBs (polychlorinated biphenyls) and gists. The use of over-the-counter and prescription drugs has
many pesticides, such as DDT. Current research implicates risen in recent years, particularly in industrialized nations.
many of these compounds in endocrine system disruption People who consume such products excrete residual chemi-
in numerous animal species, including humans. Biological cals in their waste and may also dispose of unused drugs
magnification of PCBs has been found in the food web of the
Great Lakes, where the concentration of PCBs in herring gull Figure 56.26  Rachel
eggs, at the top of the food web, is nearly 5,000 times that in Carson. Through her writing
phytoplankton, at the base (Figure 56.25). and her testimony before the U.S.
Congress, biologist and author
An infamous case of biological magnification that harmed Carson helped promote a new
top-level carnivores involved DDT, a chemical used to con- environmental ethic. Her efforts led
trol insects such as mosquitoes and agricultural pests. In the to a ban on DDT use in the United
decade after World War II, the use of DDT grew rapidly; its States and stronger controls on the
ecological consequences were not yet fully understood. By use of other chemicals.
the 1950s, scientists were learning that DDT persists in the
environment and is transported by water to areas far from
where it is applied. One of the first signs that DDT was a seri-
ous environmental problem was a decline in the populations
of pelicans, ospreys, and eagles, birds that feed at the top of
food webs. The accumulation of DDT (and DDE, a product
of its breakdown) in the tissues of these birds interfered with
the deposition of calcium in their eggshells. When the birds
tried to incubate their eggs, the weight of the parents broke
the shells of affected eggs, resulting in catastrophic declines
in the birds’ reproduction rates. Rachel Carson’s book Silent
Spring helped bring the problem to public attention in the
1960s (Figure 56.26), and DDT was banned in the United
States in 1971. A dramatic recovery in populations of the
affected bird species followed.

1274 unit eight  Ecology

improperly, such as in their Figure 56.27  Sources and movements of pharmaceuticals in the environment.

toilets or sinks. Drugs that are

not broken down in sewage

treatment plants may then enter Pharmaceuticals

r­ ivers and lakes with the material Farm animals
discharged from these plants.
Growth-promoting drugs given Toilet Humans
to farm animals can also enter
rivers and lakes with agricultural Manure Agricultural
runoff
Sludge

runoff. As a consequence, many Farms

pharmaceuticals are spreading Treated effluent
in low concentrations across the

world’s freshwater ecosystems Sewage Lakes and rivers
(Figure 56.27). treatment plant

Among the pharmaceuticals

that ecologists are studying are

the sex steroids, including forms

of estrogen used for birth control.

Some fish species are so ­sensitive to certain estrogens that con- concentration of CO2 in the atmosphere has been increasing
centrations of a few parts per trillion in their water can alter sex- as a result of the burning of fossil fuels and deforestation.

ual differentiation and shift the female-to-male sex ratio toward Scientists estimate that the average CO2 concentration in
females. Researchers in Ontario, Canada, conducted a seven- the atmosphere before 1850 was about 274 ppm. In 1958,

year experiment in which they applied the synthetic estrogen a monitoring station began taking very accurate measure-

used in contraceptives to a lake in very low concentrations (5–6 ments on Hawaii’s Mauna Loa peak, a location far from

ng/L). They found that chronic exposure of the fathead min- cities and high enough for the atmosphere to be well mixed.

now (Pimephales promelas) to the estrogen led to feminization As shown in Figure 56.28, at that time, the average CO2
of males and a near extinction of the population of this species

from the lake. Figure 56.28  Increase in atmospheric carbon dioxide
Many toxins cannot be degraded by microorganisms
concentration at Mauna Loa, Hawaii, and average global
and persist in the environment for years or even decades. temperatures. Aside from normal seasonal fluctuations, the CO2
In other cases, chemicals released into the environment concentration (blue curve) increased steadily from 1958 to 2015.
may be relatively harmless but are converted to more toxic Though average global temperatures (red curve) fluctuated a great
products by reaction with other substances, by exposure to deal over the same period, there is a clear warming trend.

light, or by the metabolism of microorganisms. Mercury, a 400 14.7

by-product of plastic production and coal-fired power gen- 390 14.6
eration, has been routinely expelled into rivers and the sea

in an insoluble form. Bacteria in the bottom mud convert CO2 concentration (ppm)380CO2 14.5
the waste to methyl­mercury (CH3Hg+), an extremely toxic Average global temperature (°C)37014.4
water-soluble compound that accumulates in the tissues of 360 14.3
organisms, including humans who consume fish from the
contaminated waters.

350 14.2

Greenhouse Gases and Climate Change 340 14.1

Human activities release a variety of gaseous waste products. 330 Temperature 14.0
People once thought that the vast atmosphere could absorb
these materials indefinitely, but we now know that such 320 13.9
additions can lead to climate change, a directional change
to the global climate that lasts for three decades or more 310 13.8
(as opposed to short-term changes in the weather).
300 13.7
Rising Atmospheric CO2 Levels 1960‘65 ‘70 ‘75 ‘80 ‘85 ‘90 ‘952000 ‘05 ‘10 ‘15
Year
To see how human actions can cause climate change, con-
sider atmospheric CO2 levels. Over the past 150 years, the MP3 Tutor: Global Warming

chapter 56  Conservation Biology and Global Change 1275

Scientific Skills Exercise ▶ A researcher
samples the air at
Graphing Cyclic Data the Mauna Loa
monitoring
How Does the Atmospheric CO2 Concentration Change station, Hawaii.
During a Year and from Decade to Decade?  The blue curve
in Figure 56.28 shows how the concentration of CO2 in Earth’s Interpret The Data
atmosphere has changed over a span of more than 50 years. For 1. Plot the data for each of the three years on one graph (producing
each year in that span, two data points are plotted, one in May
and one in November. A more detailed picture of the change in three curves). Select a type of graph that is appropriate for these
CO2 concentration can be obtained by looking at measurements data, and choose a vertical axis scale that allows you to clearly see
made at more frequent intervals. In this exercise, you’ll graph the patterns of CO2 concentration changes, both during each year
monthly CO2 concentrations for each of three one-year periods. and from decade to decade. (For additional information about
graphs, see the Scientific Skills Review in Appendix F.)
Data from the Study  The data in the table below are average 2. Within each year, what is the pattern of change in CO2 concen-
CO2 concentrations (in parts per million) at the Mauna Loa monitor- tration? Why might this pattern occur?
ing station for each month in 1990, 2000, and 2010. 3. The measurements taken at Mauna Loa represent average atmo-
spheric CO2 concentrations for the Northern Hemisphere. Suppose
Month 1990 2000 2010 you could measure CO2 concentrations under similar conditions in
the Southern Hemisphere. What pattern would you expect to see
January 353.79 369.25 388.45 in those measurements over the course of a year? Explain.
February 354.88 369.50 389.82 4. In addition to the changes within each year, what changes in CO2
March 355.65 370.56 391.08 concentration occurred between 1990 and 2010? Calculate the
April 356.27 371.82 392.46 average CO2 concentration for the 12 months of each year. By
May 359.29 371.51 392.95 what percentage did this average change from 1990 to 2000 and
June 356.32 371.71 392.06 from 1990 to 2010?
July 354.88 369.85 390.13
August 352.89 368.20 388.15 Instructors: A version of this Scientific Skills Exercise can be
September 351.28 366.91 386.80 assigned in MasteringBiology.
October 351.59 366.91 387.18
November 353.05 366.99 388.59
December 354.27 369.67 389.68

Data from  National Oceanic & Atmospheric Administration, Earth System Research
Laboratory, Global Monitoring Division.

concentration was 316 ppm. Today, it exceeds 400 ppm, an As the concentrations of CO2 and other greenhouse
increase of more than 45% since the mid-19th century. In gases rise, more solar heat is retained, thereby increasing
the Scientific Skills Exercise, you can graph and interpret the temperature of our planet. So far, Earth has warmed by
changes in CO2 concentration that occur during the course of an average of 0.9°C (1.6°F) since 1900. At the current rates
a year and over longer periods. that CO2 and other greenhouse gases are being added to the
atmosphere, global models predict an additional rise of at
The increase in the concentration of atmospheric CO2 least 3°C (5°F) by the end of the 21st century.
over the last 150 years concerns scientists because of its link
to increased global temperature. Much of the solar radiation As our planet warms, the climate is changing in other
that strikes the planet is emitted toward space as infrared ways as well: Wind and precipitation patterns are shifting,
radiation (known informally as “heat radiation”). Although and extreme weather events (such as droughts and storms)
CO2, methane, water vapor, and other greenhouse gases in are occurring more often. What are the consequences of such
the atmosphere are transparent to visible light, they inter- changes to Earth’s climate?
cept and absorb much of the infrared radiation that Earth
emits, radiating most of it back toward Earth. This process, Animation: The Global Carbon Cycle and the
called the greenhouse effect, retains some of the solar heat Greenhouse Effect
(Figure 56.29). If it were not for this greenhouse effect, the
average air temperature at Earth’s surface would be a frigid Biological Effects of Climate Change
-18°C (-0.4°F), and most life as we know it could not exist.
Many organisms, especially plants that cannot disperse
1276 unit eight  Ecology rapidly over long distances, may not be able to survive

Figure 56.29  The greenhouse effect. Carbon dioxide and other greenhouse gases the 20th century, otherwise healthy for-
in the atmosphere absorb heat emitted from Earth’s surface and then radiate much of that ests have experienced a steady increase
heat back to Earth. in the percentage of trees that die each

year. Higher temperatures and more

frequent droughts also increase the

4 Of the heat emitted likelihood of fires. In boreal forests of
from Earth, some escapes
1 Some of the to space. Much of the rest western North America and Russia, for
incoming solar is absorbed by greenhouse example, fires have burned twice the
radiation is reflected
back to space, but gases and radiated back usual area in recent decades, again lead-
most passes through toward Earth, thereby
the atmosphere to reach 1 trapping heat. ing to widespread tree mortality. As the
Earth’s surface.
4 SPACE climate continues to warm, this will
likely bring other changes in the geo-

graphic distribution of precipitation,

such as making agricultural areas of the

ATMOSPHERE central United States much drier.
Climate change has already affected
23
many other ecosystems as well. In

Europe and Asia, for example, plants

2 Of the radiation that reaches 3 Some of the energy that are producing leaves earlier in the
Earth’s surface, some is reflected warms the surface is then spring, while in tropical regions, the
back to space. Much of the rest is emitted from Earth as heat. growth and survival of some species of
absorbed, warming Earth’s surface. coral have declined as water tempera-

tures have warmed. Still other effects

the rapid climate change projected to result from global of climate change are discussed in Figure 56.30. A key take-

warming. Furthermore, many habitats today are more home message from these examples is that a given effect of

fragmented than ever, further limiting the ability of many climate change may, in turn, cause a series of other biologi-

organisms to migrate now and in the future. Indeed, the cal changes. The exact nature of such cascading effects can

climate change that has occurred to date has already altered be hard to predict, but it is clear that the more our planet

the geographic ranges of hundreds of species, in some warms, the more severely its ecosystems will be affected.

cases leading to declining population sizes and shrink- Finding Solutions to Address
ing geographic ranges (see Concept 52.1). For example, a Climate Change
2015 study of 67 species of bumblebees found that as the

climate has warmed, the geographic distributions of these We will need many approaches to slow global warming

important pollinators have decreased in size. and other aspects of climate change. Quick progress can

The ecosystems where the climate has changed the most be made by using energy more efficiently and by replacing

are those in the far north, particularly northern conifer- fossil fuels with renewable solar and wind power and, more

ous forests and tundra. As snow and ice melt and uncover controversially, with nuclear power. Today, coal, gasoline,

darker, more absorptive surfaces, these systems reflect less wood, and other organic fuels remain central to industrial-

radiation back to the atmosphere and warm further (see ized societies and cannot be burned without releasing CO2.
Figure 56.29). Arctic sea ice in the summer of 2012 covered Stabilizing CO2 emissions will require concerted interna-
the smallest area on record. Climate models suggest that tional effort and changes in both personal lifestyles and

there may be no summer ice there within a few decades, industrial processes. International negotiations have yet

decreasing habitat for polar bears, seals, and seabirds. In to reach a global consensus on how to reduce greenhouse

addition, as discussed in Concept 55.2, rising temperatures gas emissions.

have caused some Arctic regions to switch from being a CO2 Another important approach to slowing climate change is
sink (absorbing more CO2 from the atmosphere than they to reduce deforestation around the world, particularly in the
release to the atmosphere) to a CO2 source (releasing more tropics. Deforestation currently accounts for about 10% of
CO2 than they absorb)—a worrisome change that could greenhouse gas emissions. Recent research shows that paying
contribute to further climate warming. countries not to cut forests could decrease the rate of defores-

Coniferous forests in western North America have also tation by half within 10 to 20 years. Reduced deforestation

been hard hit, in this case by a combination of higher tem- would not only slow the buildup of greenhouse gases in our

peratures, decreased winter snowfall, and a lengthening of atmosphere, but also sustain native forests and preserve

the summer dry period. As a result, since the latter half of biodiversity, a positive outcome for all.

chapter 56  Conservation Biology and Global Change 1277

Figure 56.30 Make Connections
Climate Change Has Effects at All Levels of Biological Organization

The burning of fossil fuels by humans has caused atmospheric concentrations of carbon
dioxide and other greenhouse gases to rise dramatically (see Figure 56.28). This, in turn,
is changing Earth’s climate: The planet’s average temperature has increased by about
1ºC since 1900, and extreme weather events are occurring more often in some regions
of the globe. How are these changes affecting life on Earth today?

Effects on Cells Effects on Individual Organisms

Temperature affects the rates of enzymatic reactions (see Figure Organisms must maintain relatively constant internal conditions
8.17), and as a result, the rates of DNA replication, cell division, (see Concept 40.2); for example, an individual will die if its body
and other key processes in cells are affected by rising temperature becomes too high. Global warming has increased the
temperatures. risk of overheating in some species, leading to reduced food intake
and reproductive failure.
Global warming and other aspects of climate change have also
impaired some organisms’ defense responses at the cellular level. For instance, an American pika (Ochotona princeps) will die if its
For example, in the vast coniferous forests of western North body temperature rises just 3°C above its resting temperature—and
America, climate change has reduced the ability of pine trees to this can happen quickly in regions where climate change has already
defend themselves against attack by the mountain pine beetle caused significant warming.
(Dendroctonus ponderosae). ▶ As summer tempera-

Resin ◀ Pine defenses include tures have risen,
canal specialized resin cells that American pikas are
secrete a sticky substance spending more time in
(resin) that can entrap and their burrows to
kill mountain pine beetles. escape the heat.
Resin cells produce less resin Thus, they have less
in trees that are stressed by time to forage for
rising temperatures and food. Lack of food
drought conditions. has caused mortality
rates to increase and
Resin cells 100 μm birth rates to drop.
Pika populations have
▶ When beetles overwhelm a Area (km2) of pika habitat (log scale)dwindled, some to the
tree’s cellular defenses, they point of extinction. (See
produce large numbers of Figure 1.12 for another
offspring that tunnel example.)
through the wood, causing
extensive damage. Rising Each dot represents
temperatures have one pika population
shortened how long it takes
beetles to mature and 0.500
reproduce, resulting in even
more beetles. The beetles 0.050
can also infect the tree with
a harmful fungus, which 0.005 Population viable
appears as blue stains on 0.001 Population extinct
the wood.
8 10 12 14 16
◀ This aerial view shows Mean summer temperature (°C)
the scope of destruction
in one North American ▲ This graph represents conditions in 2015 at 67 sites that
forest due to mountain previously supported a pika population; the populations
pine beetles; dead trees at 10 of these sites had become extinct. Most extinctions
appear orange and red. occurred at sites with high summer temperatures and a
small area of pika habitat. As temperatures continue to
increase, more extinctions are expected.

1278 Unit eight  Ecology

Effects on Populations Effects on Communities and Ecosystems

Climate change has caused some populations to increase in size, Climate affects where species live (see Figure 52.9). Climate
while others have declined (see Concepts 1.1 and 46.1). In change has caused hundreds of species to move to new locations,
particular, as the climate has changed, some species have in some cases leading to dramatic changes in ecological commu-
adjusted when they grow, reproduce, or migrate—but others nities. Climate change has also altered primary production (see
have not, causing their populations to face food shortages and Figure 28.30) and nutrient cycling in ecosystems.
reduced survival or reproductive success.
In the example we discuss here, rising temperatures have enabled
In one example, researchers have documented a link between a sea urchin to invade southern regions along the coast of Australia,
rising temperatures and declining populations of caribou causing catastrophic changes to marine communities there.
(Rangifer tarandus) in the Arctic.
Probability of urchin reproduction (%) 20
▲ Caribou populations migrate
north in the spring to give 15
birth and to eat sprouting
plants. 10

5

0 10 12 14 16 18 20 22
8 Temperature (°C)

▲ The sea urchin Centrostephanus rodgersii requires water
temperatures above 12˚C to reproduce successfully, as shown in
this graph. As ocean waters rise above this critical temperature,
the urchin has been able to expand its range to the south,
destroying kelp beds as it moves into new regions.

▶ Alpine chickweed is an
early-flowering plant on
which caribou depend.

160 160Day of year calving begins ( ) ▲ As the urchin has expanded its range to the south, it has
150 150 Day of year plant growth begins ( ) destroyed high-diversity kelp communities, leaving bare
140 140 regions called “urchin barrens” in its wake.
130 130
120 120 MAKE CONNECTIONS In addition to causing climate
110 110 change, rising concentrations of CO2 are contributing to
ocean acidification (see Figure 3.12). Explain how ocean
2001 '02 '03 '04 '05 '06 '07 '08 '09 2010 acidification can affect individual organisms, and how
Year that, in turn, can cause dramatic changes in ecological
communities.
▲ As the climate has warmed, the plants on which caribou
depend have emerged earlier in the spring. Caribou
have not made similar changes in the timing of when
they migrate and give birth. As a result, there is a
shortage of food, and caribou offspring production has
dropped fourfold.

chapter 56  Conservation Biology and Global Change 1279

Figure 56.31  Thickness of the October ozone layer over Figure 56.32  How free chlorine in the atmosphere
Antarctica in units called Dobsons. destroys ozone.

350 Chlorine atom 1 Chlorine from CFCs interacts with ozone (O3),
forming chlorine monoxide (ClO) and
300 oxygen (O2).

250Ozone layer thickness (Dobsons) O2

200 Chlorine O3

150 O2 ClO

100 3 Sunlight causes ClO
Cl2O2 to break 2 Two ClO molecules
0 down into O2 Cl2O2
1955 ‘60 ‘65 ‘70 ‘75 ‘80 ‘85 ‘90 ‘95 2000 ‘05 ‘10 and free react, forming
Year chlorine atoms. chlorine peroxide
The chlorine (Cl2O2).
Depletion of Atmospheric Ozone atoms can begin Sunlight

Like carbon dioxide and other greenhouse gases, atmospheric the cycle again.
ozone (O3) has also changed in concentration because of
human activities. Life on Earth is protected from the damag- Figure 56.33  Erosion of Earth’s ozone shield. The ozone
ing effects of ultraviolet (UV) radiation by a layer of ozone hole over Antarctica is visible as the dark blue patch in these images
located in the stratosphere 17–25 km above Earth’s surface. based on atmospheric data.
However, satellite studies of the atmosphere show that the
springtime ozone layer over Antarctica has thinned substan- September 1979 September 2015
tially since the mid-1970s (Figure 56.31). The destruction
of atmospheric ozone results primarily from the accumula- To study the consequences of ozone depletion, ecologists
tion of chlorofluorocarbons (CFCs), chemicals once widely have conducted field experiments in which they use filters
used in refrigeration and manufacturing. In the stratosphere, to decrease or block the UV radiation in sunlight. One such
chlorine atoms released from CFCs react with ozone, reduc- experiment, performed on a scrub ecosystem near the tip of
ing it to molecular O2 (Figure 56.32). Subsequent chemical South America, showed that when the ozone hole passed over
reactions liberate the chlorine, allowing it to react with other the area, the amount of UV radiation reaching the ground
ozone molecules in a catalytic chain reaction. increased sharply, causing more DNA damage in plants that
were not protected by filters. Scientists have shown similar
The thinning of the ozone layer is most apparent over DNA damage and a reduction in phytoplankton growth when
Antarctica in spring, where cold, stable air allows the chain the ozone hole opens over the Southern Ocean (Antarctic
reaction to continue (Figure 56.33). The magnitude of ozone Ocean) each year.
depletion and the size of the ozone hole have been slightly
smaller in recent years than the average for the last 20 years, The good news about the ozone hole is how quickly
but the hole still sometimes extends as far as the southern- many countries have responded to it. Since 1987,  at least
most portions of Australia, New Zealand, and South America. 197 nations, including the United States, have signed the
At the more heavily populated middle latitudes, ozone levels Montreal Protocol, a treaty that regulates the use of ozone-
have decreased 2–10% during the past 20 years. depleting chemicals. Most nations, again including the
United States, have ended the production of CFCs. As a con-
Decreased ozone levels in the stratosphere increase the inten- sequence of these actions, chlorine concentrations in the
sity of UV rays reaching Earth’s surface. The consequences of stratosphere have stabilized and ozone depletion is slowing.
ozone depletion for life on Earth may be severe for plants, ani-
mals, and microorganisms. Some scientists expect increases in
both lethal and nonlethal forms of skin cancer and in cataracts
among humans, as well as unpredictable effects on crops and
natural communities, especially the phytoplankton that are
responsible for a large proportion of Earth’s primary production.

1280 unit eight  Ecology

But even though CFC emissions today are close to zero, includes studies of global change, including interactions
c­ hlorine molecules already in the atmosphere will continue between climate and ecological processes, biological diversity
to influence stratospheric ozone levels for at least 50 years. and its role in maintaining ecological processes, and the ways
in which the productivity of natural and artificial ecosystems
The partial destruction of Earth’s ozone shield is one more can be sustained. This initiative requires a strong commit-
example of how greatly humans can disrupt the dynamics of ment of human and economic resources.
ecosystems and the biosphere. It also highlights our ability to
solve environmental problems when we set our minds to it. Achieving sustainable development is an ambitious goal.
To sustain ecosystem processes and stem the loss of biodi-
Concept Check 56.4 versity, we must connect life science with the social sciences,
economics, and the humanities. We must also reassess our
1. How can the addition of excess mineral nutrients to a personal values. Those of us living in wealthier nations have
lake threaten its fish population? a larger ecological footprint than do people living in develop-
ing nations (see Concept 53.6). By including the long-term
2. MAKE CONNECTIONS There are vast stores of organic costs of consumption in our decision-making processes, we
matter in the soils of northern coniferous forests and can learn to value the ecosystem services that sustain us. The
tundra around the world. Suggest an explanation for following case study illustrates how the combination of scien-
why scientists who study global warming are closely tific and personal efforts can make a significant difference in
monitoring these stores (see Figure 55.14). creating a truly sustainable world.

3. MAKE CONNECTIONS Mutagens are chemical and Case Study: Sustainable Development
physical agents that induce mutations in DNA (see in Costa Rica
Concept 17.5). How does reduced ozone concentration
in the atmosphere increase the likelihood of mutations The success of conservation in Costa Rica (see Concept 56.3) has
in various organisms? required a partnership between the national government, non-
government organizations (NGOs), and private citizens. Many
For suggested answers, see Appendix A. nature reserves established by individuals have been recognized
by the government as national wildlife reserves and given sig-
Concept  56.5 nificant tax benefits. However, conservation and restoration
of biodiversity make up only one facet of sustainable develop-
Sustainable development can ment; the other key facet is improving the human condition.
improve human lives while
conserving biodiversity How have the living conditions of the Costa Rican people
changed as the country has pursued its conservation goals?
With the increasing loss and fragmentation of habitats, Two of the most fundamental indicators of living conditions
changes in Earth’s physical environment and climate, and are infant mortality rate and life expectancy (see Concept 53.6).
increasing human population (see Concept 53.6), we face dif- As shown in Figure 56.34, from 1930 to 2010, the infant
ficult trade-offs in managing the world’s resources. Preserving
all habitat patches isn’t feasible, so biologists must help soci- Figure 56.34  Infant mortality and life expectancy
eties set conservation priorities by identifying which habitat at birth in Costa Rica.
patches are most crucial. Ideally, implementing these priori-
ties should also improve the quality of life for local people. 200 Infant mortality 80
Ecologists use the concept of sustainability as a tool to estab- Life expectancy
lish long-term conservation priorities. Infant mortality (per 1,000 live births)
Life expectancy (years)
Sustainable Development 70
150
We need to understand the interconnections of the biosphere
if we are to protect species from extinction and improve the 60
quality of human life. To this end, many nations, scientific 100
societies, and other groups have embraced the concept of
sustainable development, economic development that 50
meets the needs of people today without limiting the ability
of future generations to meet their needs. For example, 50
the Ecological Society of America, the world’s largest organi- 40
zation of professional ecologists, endorses a research agenda
called the Sustainable Biosphere Initiative. The goal of this 0 1950 1975 30
initiative is to define and acquire the basic ecological infor- 1925 2000
mation needed to develop, manage, and conserve Earth’s
resources as responsibly as possible. The research agenda Year

chapter 56  Conservation Biology and Global Change 1281

mortality rate in Costa Rica declined from 170 to 9 per 1,000 reverence for the natural world is evident in the early murals
live births; over the same period, life expectancy increased of wildlife they painted on cave walls (Figure 56.35a) and in
from about 43 years to 79 years. Another indicator of living the stylized visions of life they sculpted from bone and ivory
conditions is the literacy rate. The 2011 literacy rate in Costa (Figure 56.35b).
Rica was 96%, compared to an average of 82% in the other
six Central American countries. Such statistics show that liv- Our lives reflect remnants of our ancestral attachment to
ing conditions in Costa Rica have improved greatly over the nature and the diversity of life—the concept of biophilia that
period in which the country has dedicated itself to conserva- was introduced early in this chapter. We evolved in natu-
tion and restoration. While this result does not prove that ral environments rich in biodiversity, and we still have an
conservation causes an improvement in human welfare, we affinity for such settings (Figure 56.35c and d). Indeed, our
can say with certainty that development in Costa Rica has biophilia may be innate, an evolutionary product of natural
attended to both nature and people. selection acting on a brainy species whose survival depended
on a close connection to the environment and a practical
The Future of the Biosphere appreciation of plants and animals.

Our modern lives are very different from those of early Our appreciation of life guides the field of biology today.
humans, who hunted and gathered to survive. Their We celebrate life by deciphering the genetic code that makes
each species unique. We embrace life by using fossils and
Figure 56.35  Biophilia, past and present. DNA to chronicle evolution through time. We preserve life
through our efforts to classify and protect the millions of
(a) Detail of animals ­species on Earth. We respect life by using nature responsibly
in a 17,000-year-old and reverently to improve human welfare.
cave painting,
Lascaux, France Biology is the scientific expression of our desire to know
nature. We are most likely to protect what we appreciate,
(b) A 30,000-year-old ivory and we are most likely to appreciate what we understand.
carving of a water bird, By learning about the processes and diversity of life, we
found in Germany also become more aware of ourselves and our place in the
biosphere. We hope this text has served you well in this
­lifelong adventure.

Concept Check 56.5

1. What is meant by the term sustainable development?
2. How might biophilia influence us to conserve species and

restore ecosystems?
3. WHAT IF? Suppose a new fishery is discovered, and

you are put in charge of developing it sustainably. What
ecological data might you want on the fish popula-
tion? What criteria would you apply for the fishery’s
development?

For suggested answers, see Appendix A.

(d) A young biologist
holding a songbird

(c) Nature lovers on a
wildlife-watching
expedition

1282 unit eight  Ecology

56 Chapter Review Go to MasteringBiology™ for Videos, Animations, Vocab Self-Quiz,
Practice Tests, and more in the Study Area.

Summary of Key Concepts Concept  56.3
Concept  56.1
Landscape and regional conservation
Human activities threaten Earth’s help sustain biodiversity (pp. 1268–1272)
biodiversity (pp. 1259–1264)
Vocab The structure of a landscape can strongly influence biodiversity.
Biodiversity can be considered at three main levels: Self-Quiz As habitat fragmentation increases and edges become more
goo.gl/6u55ks extensive, biodiversity tends to decrease. Movement corridors
can promote dispersal and help sustain populations.

Biodiversity hot spots are also hot spots of extinction and thus
prime candidates for protection. Sustaining biodiversity in parks
and reserves requires management to ensure that human activities
in the surrounding landscape do not harm the protected habitats.
The zoned reserve model recognizes that conservation efforts
often involve working in landscapes that are greatly affected by
human activity.

Urban ecology is the study of organisms and their environment
in primarily urban settings.

Genetic diversity: enables adaptation to environmental change ? Give two examples that show how habitat fragmentation can harm
species in the long term.

Concept  56.4

Earth is changing rapidly as a result
of human actions (pp. 1272–1281)

Species diversity: maintains communities and food webs Agriculture removes plant nutrients from ecosystems, so large
supplements are usually required. The nutrients in fertilizer can
Ecosystem diversity: provides life-sustaining services pollute groundwater and surface-water aquatic ecosystems, where
they can stimulate excess algal growth (eutrophication).
Our biophilia enables us to recognize the value of biodiversity for
its own sake. Other species also provide humans with food, fiber, The release of toxic wastes and pharmaceuticals has polluted the
medicines, and ecosystem services. environment with harmful substances that often persist for long
periods and become increasingly concentrated in successively
Four major threats to biodiversity are habitat loss, introduced higher trophic levels of food webs (biological magnification).
species, overharvesting, and global change.
Because of the burning of fossil fuels and other human activities,
the atmospheric concentration of CO2 and other greenhouse
gases has been steadily increasing. These increases have caused
climate change, including significant global warming and
changing patterns of precipitation. Climate change has already
affected many ecosystems.

The ozone layer reduces the penetration of UV radiation through
the atmosphere. Human activities, notably the release of chlorine-
containing pollutants, have eroded the ozone layer, but govern-
ment policies are helping to solve the problem.

? Give at least three examples of key ecosystem services that nature ? Thinking about biological magnification of toxins, is it healthier to feed
provides for people. at a lower or higher trophic level? Explain.

Concept  56.2 Concept  56.5

Population conservation focuses on population Sustainable development can improve human
size, genetic diversity, and critical habitat lives while conserving biodiversity (pp. 1281–1282)
(pp. 1264–1268)
The goal of the Sustainable Biosphere Initiative is to acquire the
When a population drops below a minimum viable popula- ecological information needed for the development, manage-
tion (MVP) size, its loss of genetic variation due to nonrandom ment, and conservation of Earth’s resources.
mating and genetic drift can trap it in an extinction vortex.
Costa Rica’s success in conserving tropical biodiversity has
The declining-population approach focuses on the environmental involved a partnership among the government, other organiza-
factors that cause decline, regardless of absolute population size. tions, and private citizens. Human living conditions in Costa Rica
It follows a step-by-step conservation strategy. have improved along with ecological conservation.

Conserving species often requires resolving conflicts between the By learning about biological processes and the diversity of life, we
habitat needs of endangered species and human demands. become more aware of our close connection to the environment
and the value of other organisms that share it.
? Why is the minimum viable population size smaller for a genetically
diverse population than for a less genetically diverse population? ? Why is sustainability such an important goal for conservation biologists?

chapter 56  Conservation Biology and Global Change 1283

Test Your Understanding southwest corner, and intact forest everywhere else. You must
build a road, 10 m by 3,000 m, from the north to the south
Level 1: Knowledge/Comprehension side of the reserve and construct a maintenance building that
will take up 100 m2 in the reserve. Draw a map of the reserve,
1. One characteristic that distinguishes a population PRACTICE showing where you would put the road and the building
in an extinction vortex from most other TEST to minimize cowbird intrusion along edges. Explain your
populations is that reasoning.
(A) it is a rare, top-level predator. goo.gl/CUYGKD 8. EVOLUTION CONNECTION  The fossil record indicates that there
(B) its effective population size is lower than its have been five mass extinction events in the past 500 million
total population size. years (see Concept 25.4). Many ecologists think we are on the
(C) its genetic diversity is very low. verge of entering a sixth mass extinction event. Briefly discuss
(D) it is not well adapted to edge conditions. the history of mass extinctions and the length of time it typically
takes for species diversity to recover through the process of
2. The main cause of the increase in the amount of CO2 in Earth’s evolution. Explain why this should motivate us to slow the
atmosphere over the past 150 years is loss of biodiversity today.
(A) increased worldwide primary production. 9. SCIENTIFIC INQUIRY  (a) Estimate the average CO2 concentration
(B) increased worldwide standing crop. in 1975 and in 2012 using data provided in Figure 56.28. 
(C) an increase in the amount of infrared radiation absorbed (b) On average, how rapidly did CO2 concentration increase
by the atmosphere. (ppm/yr) from 1975 to 2012?  (c) Estimate the approximate
(D) the burning of larger amounts of wood and fossil fuels. CO2 concentration in 2100, assuming that the CO2 concentration
continues to rise as fast as it did from 1975 to 2012.  (d) Draw
3. What is the single greatest threat to biodiversity? a graph of average CO2 concentration from 1975 to 2012 and
(A) overharvesting of commercially important species then use a dashed line to extend the graph to the year 2100. 
(B) habitat alteration, fragmentation, and destruction (e) Identify the ecological factors and human decisions that
(C) introduced species that compete with native species might influence the actual rise in CO2 concentration. 
(D) novel pathogens (f) Discuss how additional scientific data could help societies
predict this value.
Level 2: Application/Analysis 10. WRITE ABOUT A THEME: INTERACTIONS  One factor
favoring rapid population growth by an introduced species
4. Which of the following is a consequence of biological is the absence of the predators, parasites, and pathogens that
magnification? controlled its population in the region where it evolved. In a
(A) Toxic chemicals in the environment pose greater risk to short essay (100–150 words), explain how evolution by natural
top-level predators than to primary consumers. selection in a region of introduction would influence the rate
(B) Populations of top-level predators are generally smaller at which native predators, parasites, and pathogens attack an
than populations of primary consumers. introduced species.
(C) The biomass of producers in an ecosystem is generally 11. Synthesize Your Knowledge
higher than the biomass of primary consumers.
(D) Only a small portion of the energy captured by producers Big cats, such as the Siberian tiger (Panthera tigris altaica)
is transferred to consumers. shown here, are one of the most endangered groups of
mammals in the world. Based on what you’ve learned in this
5. Which of the following strategies would most rapidly increase chapter, discuss some of the approaches you would use to help
the genetic diversity of a population in an extinction vortex? preserve them.
(A) Establish a reserve that protects the population’s habitat. For selected answers, see Appendix A.
(B) Introduce new individuals transported from other popula-
tions of the same species. For additional practice questions, check out the Dynamic Study
(C) Sterilize the least fit individuals in the population. Modules in MasteringBiology. You can use them to study on
(D) Control populations of the endangered population’s your smartphone, tablet, or computer anytime, anywhere!
predators and competitors.

6. Of the following statements about protected areas that have
been established to preserve biodiversity, which one is not
correct?
(A) About 25% of Earth’s land area is now protected.
(B) National parks are one of many types of protected areas.
(C) Management of a protected area should be coordinated
with management of the land surrounding the area.
(D) It is especially important to protect biodiversity hot spots.

Level 3: Synthesis/Evaluation

7. DRAW IT  Suppose that you are managing a forest reserve, and
one of your goals is to protect local populations of woodland
birds from parasitism by the brown-headed cowbird. You
know that female cowbirds usually do not venture more than
about 100 m into a forest and that nest parasitism is reduced
when woodland birds nest away from forest edges. The reserve
you manage extends about 6,000 m from east to west and
3,000 m from north to south. It is surrounded by a deforested
pasture on the west, an agricultural field for 500 m in the

1284 unit eight  Ecology

AA p p e n d i x Answers

NOTE: Answers to Scientific Skills Exercises, Problem-Solving Exercises, Interpret with the beaks of a shape best at picking up insects would eat more and have more
the Data questions, and short-answer essay questions are available only for in- offspring. Therefore, the green warbler finch of today has a slender beak that is
structors in the Instructor Resources area of MasteringBiology. Scientific Skills very well matched (adapted) to its food source, insects. 
Exercises, Problem-Solving Exercises, Interpret the Data questions, and additional 3.
questions for the Visualizing Figures can be assigned and automatically graded in
MasteringBiology. Concept Check 1.3 Appendix A  Answers

Chapter 1 1. Mouse coat color matches the environment for both beach and inland popula-
tions.  2. Inductive reasoning derives generalizations from specific cases; deduc-
Figure Questions tive reasoning predicts specific outcomes from general premises.  3. Compared
to a hypothesis, a scientific theory is usually more general and substantiated by a
Figure 1.4 The scale bar is about 8.5 mm long, and it corresponds to 1 µm. The pro- much greater amount of evidence. Natural selection is an explanatory idea that
karyotic cell is about 2 cm = 20 mm long. Dividing by 8.5 mm/scale bar, the length applies to all kinds of organisms and is supported by vast amounts of evidence of
of the prokaryotic cell is about 2.4 scale bars. Each scale bar represents 1 µm, so the various kinds.  4. Based on the mouse coloration in Figure  1.25, you might expect
prokaryotic cell is about 2.4 µm long. The eukaryotic cell is about 82 mm across that the mice that live on the sandy soil would be lighter in color and those that
(from lower left to upper right) divided by 8.5 mm/scale bar = 9.6 scale bars = 9.6 µm live on the lava rock would be much darker. And in fact, that is what researchers
across.  Figure 1.10 The response to insulin is glucose uptake by cells and glucose have found. You would predict that each color of mouse would be less preyed
storage in liver cells. The initial stimulus is high glucose levels, which are reduced upon in its native habitat than it would be in the other habitat. (Research results
when glucose is taken up by cells.  also support this prediction.) You could repeat the Hoekstra experiment with
Figure 1.18 colored models, painted to resemble these two types of mouse. Or you could try
transplanting some of each population to its non-native habitat and counting
As the soil gradually becomes lighter how many you can recapture over the next few days, then comparing the four
brown, beetles that match the color of samples as was done in Hoekstra’s experiment. (The painted models are easier to
the soil will not be seen by birds and recapture, of course!) In the live mouse transplantation experiment, you would
therefore will not be eaten. For example, have to do controls to eliminate the variable represented by the transplanted mice
when the soil is medium-colored, birds being in a new, unknown territory. You could control for the transplantation pro-
will be able to see and eat the darker cess by transplanting some dark mice from one area of lava rock to one far distant,
beetles and any lighter beetles that arise. and some light mice from one area of sandy soil to a distant area.
(Most or all of the lighter beetles will
have been eaten earlier, but new light Concept Check 1.4
beetles will arise due to variation in
the population.) Thus, over time, the 1. Science aims to understand natural phenomena and how they work, while
population will become lighter as the soil technology involves application of scientific discoveries for a particular purpose
becomes lighter. or to solve a specific problem. 2. Natural selection could be operating. Malaria is
present in sub-Saharan Africa, so there might be an advantage to people with the
5 Environmental change resulting in sickle-cell disease form of the gene that makes them more able to survive and pass
survival of organisms with different traits on their genes to offspring. Among those of African descent living in the United
States, where malaria is absent, there would be no advantage, so they would be
Concept Check 1.1 selected against more strongly, resulting in fewer individuals with the sickle-cell
disease form of the gene.
1. Examples: A molecule consists of atoms bonded together. Each organelle has
an orderly arrangement of molecules. Photosynthetic plant cells contain organelles Summary of Key Concepts Questions
called chloroplasts. A tissue consists of a group of similar cells. Organs such as the
heart are constructed from several tissues. A complex multicellular organism, such 1.1 Finger movements rely on the coordination of the many structural compo-
as a plant, has several types of organs, such as leaves and roots. A population is a nents of the hand (muscles, nerves, bones, etc.), each of which is composed of
set of organisms of the same species. A community consists of populations of the elements from lower levels of biological organization (cells, molecules). The devel-
various species inhabiting a specific area. An ecosystem consists of a biological opment of the hand relies on the genetic information encoded in chromosomes
community along with the nonliving factors important to life, such as air, soil, and found in cells throughout the body. To power the finger movements that result in
water. The biosphere is made up of all of Earth’s ecosystems. 2. (a) New properties a text message, muscle and nerve cells require chemical energy that they transform
emerge at successive levels of biological organization: Structure and function are in powering muscle contraction or in propagating nerve impulses. Texting is in
correlated. (b) Life’s processes involve the expression and transmission of genetic essence communication, an interaction that conveys information between organ-
information. (c) Life requires the transfer and transformation of energy and matter.  isms, in this case of the same species.  1.2 Ancestors of the beach mouse may
3. Some possible answers: Organization (Emergent properties): The ability of a human have exhibited variations in their coat color. Because of the prevalence of visual
heart to pump blood requires an intact heart; it is not a capability of any of the predators, the better-camouflaged (lighter) mice in the beach habitat may have
heart’s tissues or cells working alone. Organization (Structure and function): The survived longer and been able to produce more offspring. Over time, a higher and
strong, sharp teeth of a wolf are well suited to grasping and dismembering its higher proportion of individuals in the population would have had the adapta-
prey. Information: Human eye color is determined by the combination of genes tion of lighter fur that acted to camouflage the mouse in the beach habitat. 
inherited from the two parents. Energy and Matter: A plant, such as a grass, absorbs 1.3 Gathering and interpreting data are core activities in the scientific process,
energy from the sun and transforms it into molecules that act as stored fuel. and they are affected by, and affect in turn, three other arenas of the scientific
Animals can eat parts of the plant and use the food for energy to carry out their process: exploration and discovery, community analysis and feedback, and soci-
activities. Interactions (Molecules): When your stomach is full, it signals your brain etal benefits and outcomes.  1.4 Different approaches taken by scientists studying
to decrease your appetite. Interactions (Ecosystems): A mouse eats food, such as natural phenomena at different levels complement each other, so more is learned
nuts or grasses, and deposits some of the food material as wastes (feces and urine). about each problem being studied. A diversity of backgrounds among scientists
Construction of a nest rearranges the physical environment and may hasten deg- may lead to fruitful ideas in the same way that important innovations have often
radation of some of its components. The mouse may also act as food for a predator. arisen where a mix of cultures coexist, due to multiple different viewpoints.

Concept Check 1.2 Test Your Understanding

1. The naturally occurring heritable variation in a population is “edited” by 1. B  2. C 3. C 4. B 5. C 6. A 7. D 8. Your figure should show the fol-
natural selection because individuals with heritable traits better suited to the lowing: (1) for the biosphere, the Earth with an arrow coming out of a tropical
environment survive and reproduce more successfully than others. Over time, ocean; (2) for the ecosystem, a distant view of a coral reef; (3) for the community,
better-suited individuals persist and their percentage in the population increases, a ­collection of reef animals and algae, with corals, fishes, some seaweed, and any
while less well-suited individuals become less prevalent—a type of population other organisms you can think of; (4) for the population, a group of fish of the same
editing. 2. Here is one possible explanation: The ancestor species of the green species; (5) for the organism, one fish from your population; (6) for the organ, the
warbler finch lived on an island where insects were a plentiful food source. Among fish’s stomach; (7) for a tissue, a group of similar cells from the stomach; (8) for a
individuals in the ancestor population, there was likely variation in beak shape cell, one cell from the tissue, showing its nucleus and a few other organelles; (9) for
and size. Individuals with slender, sharp beaks were likely more successful at pick- an organelle, the nucleus, where most of the cell’s DNA is located; and (10) for a
ing up insects for food. Being well-nourished, they gave rise to more offspring molecule, a DNA double helix. Your sketches can be very rough!
than birds with thick, short beaks. Their many offspring inherited slender, sharp
beaks (because of genetic information being passed from generation to genera- appendix A  Answers A-1
tion, although Darwin didn’t know this). In each generation, the offspring birds

Chapter 2 2.2
Both neon and argon have completed
Figure Questions valence shells, containing 8 electrons.
They do not have unpaired electrons
Figure 2.7 Atomic number = 12; 12 protons, 12 electrons; 3 electron shells; that could participate in chemical
2 valence electrons  bonds. 
Figure 2.14 One possible answer: Figure 2.17
2.3 Electrons are shared equally between the two atoms in a nonpolar covalent
Leaf Bubbles of O2 bond. In a polar covalent bond, the electrons are drawn closer to the more electro-
negative atom. In the formation of ions, an electron is completely transferred from
Appendix A  Answers one atom to a much more electronegative atom.  2.4 The concentration of prod-
ucts would increase as the added reactants were converted to products. Eventually,
an equilibrium would again be reached in which the forward and reverse reactions
were proceeding at the same rate and the relative concentrations of reactants and
products returned to where they were before the addition of more reactants.

Test Your Understanding

1. A  2. D  3. B  4. A  5. D  6. B  7. C  8. D 
9.

Concept Check 2.1 Chapter 3 δ+ δ+

1. Table salt (sodium chloride) is made up of sodium and chlorine. We are able to Figure Questions H H
eat the compound, showing that it has different properties from those of a metal
(sodium) and a poisonous gas (chlorine).  2. Yes, because an organism requires Figure 3.2 One possible answer: O
trace elements, even though only in small amounts  3. A person with an iron
deficiency will probably show fatigue and other effects of a low oxygen level in the δ– δ– Hydrogen
blood. (The condition is called anemia and can also result from too few red blood bond
cells or abnormal hemoglobin.)  4. Variant ancestral plants that could tolerate δ+
elevated levels of the elements in serpentine soils could grow and reproduce there.
(Plants that were well adapted to nonserpentine soils would not be expected to H Polar covalent
survive in serpentine areas.) The offspring of the variants would also vary, with bonds
those most capable of thriving under serpentine conditions growing best and δ+ δ– O
reproducing most. Over many generations, this probably led to the serpentine- H
adapted species we see today.
δ– δ+
Concept Check 2.2 δ+ δ–

1. 7  2.  175N  3. 9 electrons; two electron shells; 1s, 2s, 2p (three orbitals); 1 electron Figure 3.6 Without hydrogen bonds, water would behave like other small mol-
is needed to fill the valence shell.  4. The elements in a row all have the same ecules, and the solid phase (ice) would be denser than liquid water. The ice would
number of electron shells. In a column, all the elements have the same number sink to the bottom and would no longer insulate the whole body of water, which
of electrons in their valence shells. would eventually freeze because of the freezing temperatures in the Southern
Ocean near Antarctica. The krill would not survive.  Figure 3.8 Heating the solu-
Concept Check 2.3 tion would cause the water to evaporate faster than it is evaporating at room tem-
perature. At a certain point, there wouldn’t be enough water molecules to dissolve
1. In this structure, each carbon atom has only three covalent bonds instead of the the salt ions. The salt would start coming out of solution and re-forming crystals.
required four.  2. The attraction between oppositely charged ions, forming ionic Eventually, all the water would evaporate, leaving behind a pile of salt like the
bonds  3. If you could synthesize molecules that mimic these shapes, you might original pile.  Figure 3.12 Adding excess CO2 to the oceans ultimately reduces the
be able to treat diseases or conditions caused by the inability of affected individuals rate at which calcification (by organisms) can occur.
to synthesize such molecules.
Concept Check 3.1
Concept Check 2.4
1. Electronegativity is the attraction of an atom for the electrons of a covalent
1. bond. Because oxygen is more electronegative than hydrogen, the oxygen atom
in H2O pulls electrons toward itself, resulting in a partial negative charge on
2. At equilibrium, the forward and reverse reactions occur at the same rate. the oxygen atom and partial positive charges on the hydrogen atoms. Atoms
3. C6H12O6 + 6 O2 S 6 CO2 + 6 H2O + Energy. Glucose and oxygen react to form in neighboring water molecules with opposite partial charges are attracted to
carbon dioxide and water, releasing energy. We breathe in oxygen because we each other, forming a hydrogen bond. 2. Due to its two polar covalent bonds,
need it for this reaction to occur, and we breathe out carbon dioxide because it is a water molecule has four regions of partial charge: two positive regions on
a by-product of this reaction. (This reaction is called cellular respiration, and you the two hydrogens and two negative regions on the oxygen atom. Each of these
will learn more about it in Chapter 9.) can bind to a region of opposite partial charge on another water molecule. 
3. The hydrogen atoms of one molecule, with their partial positive charges,
Summary of Key Concepts Questions would repel the hydrogen atoms of the adjacent molecule. 4. The covalent
bonds of water molecules would not be polar, so no regions of the molecule
2.1 A compound is made up of two or more elements combined in a fixed ratio, would carry partial charges and water molecules would not form hydrogen
while an element is a substance that cannot be broken down to other substances.  bonds with each other.

Concept Check 3.2

1. Hydrogen bonds hold neighboring water molecules together. This cohesion
helps chains of water molecules move upward against gravity in water-conducting

A-2    appendix A Answers

cells as water evaporates from the leaves. Adhesion between water molecules Chapter 4 Appendix A  Answers
and the walls of the water-conducting cells also helps counter gravity. 2. High
humidity hampers cooling by suppressing the evaporation of sweat. 3. As water Figure Questions
freezes, it expands because water molecules move farther apart in forming ice
crystals. When there is water in a crevice of a boulder, expansion due to freezing Figure 4.2 Because the concentration of the reactants influences the equilibrium
may crack the boulder. 4. The hydrophobic substance repels water, perhaps (as discussed in Concept 2.4), there might have been more HCN relative to CH2O,
helping to keep the ends of the legs from becoming coated with water and breaking since there would have been a higher concentration of the reactant gas containing
through the surface. If the legs were coated with a hydrophilic substance, water nitrogen.
would be drawn up them, possibly making it more difficult for the water strider to Figure 4.4
walk on water.
Figure 4.6 The tails of fats contain only carbon-hydrogen bonds, which are rela-
Concept Check 3.3 tively nonpolar. Because the tails occupy the bulk of a fat molecule, they make the
1. 105, or 100,000 2. [H+] = 0.01 M  = 10-2 M, so pH = 2. 3. CH3COOH S molecule as a whole nonpolar and therefore incapable of forming hydrogen bonds
with water.
CH3COO- + H+. CH3COOH is the acid (the H+ donor), and CH3COO- is the base Figure 4.7
(the H+ acceptor). 4. The pH of the water should decrease from 7 to about 2
(as mentioned in the text); the pH of the acetic acid solution will decrease only a
small amount, because as a weak acid, it acts (like carbonic acid) as a buffer. The
reaction shown for question 3 will shift to the left, with CH3COO- accepting the
influx of H+ and becoming CH3COOH molecules.

Summary of Key Concepts Questions

3.1

δ– Concept Check 4.1

δ+ 1. Prior to Wöhler’s experiment, the prevailing view was that only living organ-
H isms could synthesize “organic” compounds. Wöhler made urea, an organic com-
pound, without the involvement of living organisms. 2. The sparks provided
δ+ δ– O energy needed for the inorganic molecules in the atmosphere to react with each
H other. (You’ll learn more about energy and chemical reactions in Chapter 8.)
δ– δ+
δ+ δ– Concept Check 4.2

1. 

No. A covalent bond is a strong bond in which electrons are shared between 2. The forms of C4H10 in (b) are structural isomers, as are the butenes (forms of
two atoms. A hydrogen bond is a weak bond, which does not involve electron C4H8) in (c). 3. Both consist largely of hydrocarbon chains, which provide
sharing, but is simply an attraction between two partial charges on neighboring fuel—gasoline for engines and fats for plant embryos and animals. Reactions of
atoms.  3.2 Ions dissolve in water when polar water molecules form a hydra- both types of molecules release energy. 4. No. There is not enough diversity in
tion shell around them, with partially charged regions of water molecules being propane’s atoms. It can’t form structural isomers because there is only one way
attracted to ions of the opposite charge. Polar molecules dissolve as water mol- for three carbons to attach to each other (in a line). There are no double bonds,
ecules form hydrogen bonds with them and surround them. Solutions are homo- so cis-trans isomers are not possible. Each carbon has at least two hydrogens
geneous mixtures of solute and solvent.  3.3 The concentration of hydrogen ions attached to it, so the molecule is symmetrical and cannot have enantiomers.
(H+ ) would be 10-11, and the pH of the solution would be 11.
Concept Check 4.3
Test Your Understanding
1. It has both an amino group (¬NH2), which makes it an amine, and a carboxyl
1. C 2. D 3. C 4. A 5. D  group (¬COOH), which makes it a carboxylic acid. 2. The ATP molecule loses a
6. phosphate, becoming ADP. 
3.  A chemical group that can act as a base has been
7. Due to intermolecular hydrogen bonds, water has a high specific heat (the
amount of heat required to increase the temperature of water by 1°C). When water replaced with a group that can act as an acid, increas-
is heated, much of the heat is absorbed in breaking hydrogen bonds before the ing the acidic properties of the molecule. The shape
water molecules increase their motion and the temperature increases. Conversely, of the molecule would also change, likely changing
when water is cooled, many H bonds are formed, which releases a significant the molecules with which it can interact. The original
amount of heat. This release of heat can provide some protection against freezing cysteine molecule has an asymmetric carbon in the
of the plants’ leaves, thus protecting the cells from damage.  8. Both global warm- center. After replacement of the amino group with a
ing and ocean acidification are caused by increasing levels of carbon dioxide in the carboxyl group, this carbon is no longer asymmetric.
atmosphere, the result of burning fossil fuels.
Summary of Key Concepts Questions

4.1 Miller showed that organic molecules could form under the physical and
chemical conditions estimated to have been present on early Earth. This abiotic
synthesis of organic molecules would have been a first step in the origin of life. 
4.2 Acetone and propanal are structural isomers. Acetic acid and glycine have no
asymmetric carbons, whereas glycerol phosphate has one. Therefore, glycerol
phosphate can exist as forms that are enantiomers, but acetic acid and glycine
cannot.  4.3 The methyl group is nonpolar and not reactive. The other six
groups are called functional groups because they can participate in chemical
reactions. Also, all except the sulfhydryl group are hydrophilic, increasing the
solubility of organic compounds in water.

Test Your Understanding

1. B 2. B 3. C 4. C 5. A 6. B 7. A 8. The molecule on the right; the
middle carbon is asymmetric.
9. Silicon has 4 valence electrons, the same number as carbon. Therefore,

silicon would be able to form long chains, including branches, that
could act as skeletons for large molecules. It would clearly do this much
better than neon (with no valence electrons) or aluminum (with 3
valence electrons).

appendix A  Answers A-3