Environmental Science

Interpreting Graphics

Directions (10–12): For each question below, record the correct answer on
a separate sheet of paper.

Use the table below to answer question 10.

Interactions Between Two Species

Interaction Species A Species B
Competition Fox Coyote
Predation Kit fox Kangaroo rat
Mutualism Yucca moth Yucca
Commensalism Wren Cactus

0 Which of the interactions listed in the table is harmful to both species?
F. commensalism H. mutualism

G. competition I. predation

Use the illustration below to answer questions 11 and 12.
Carrying Capacity

Population overshoots
carrying capacity

Carrying Population runs out of
capacity resources and declines

Population size Exponential Population recovers
growth and stabilizes

Population crashes

Time

q What happens to population size between the time it overshoots Test

carrying capacity to when it recovers and stabilizes? Test questions may
A. It remains stable. C. It decreases before it stabilizes. not be arranged in
B. It declines steadily. D. It continues to increase at a steady rate. order of increasing
difficulty. If you are
w If the population size was nearly 2,000 when it overshot carrying unable to answer a
question, mark it and
capacity, and 1,500 when it was at its lowest amount of decline during move on to another
question.
its recovery, what is the estimated carrying capacity of the population?

F. 1,600 H. 1,800

G. 1,750 I. 1,950

Chapter 8 Standardized Test Prep 229

8C H A P T E R Skills Practice Lab: OBSERVATION

Objectives Studying Population Growth

̈ USING SCIENTIFIC METHODS Observe, You have learned that a population will keep growing until limit-
record, and graph the growth ing factors slow or stop this growth. How do you know when a
and decline of a population of population has reached its carrying capacity? In this lab, you will
yeast cells in an experimental envi- observe the changes in a population of yeast cells. The cells will
ronment. grow in a container and have limited food over several days.

̈ USING SCIENTIFIC METHODS Predict the Procedure
carrying capacity of an environ-
ment for a population. 1. Your teacher will prepare several cultures of household baker’s
yeast (fungi of the genus Saccharomyces) in flasks. Each yeast
̈ Infer the limiting resource of an culture will have grown for a different period of time in the
environment. same type of environment. Each flask will have been prepared
with 500mL lukewarm water, 1 g of active dry yeast, and 20 g
Materials of sugar. The sugar is the only food source for the yeast.

compound microscope 2. Make two data tables like the one shown below. One table
methylene blue solution, 1% will contain your observations of living yeast cells, and the
micrometer, stage type or other table will be for observations of dead yeast cells.

eyepiece disc for microscope Cell Counts
microscope slide, with coverslip
Time (h) 1 234 Average Class Average
(5)
pipet, 1 mL (5) 0
test tube (5) 12
yeast culture, in an Erlenmeyer 24
36
flask (5) 48

DO NOT WRITE IN THIS BOOK

̈ Budding Yeast This live, budding 3. Take a sample of yeast culture from the first flask (Time 0).
yeast cell is magnified 3,025 times by Swirl the flask gently to mix the yeast cells evenly, and then
a scanning electron microscope. immediately use the pipet to transfer 1 mL of yeast culture to
a test tube. Add two drops of methylene blue solution to the
230 Chapter 8 Skills Practice Lab test tube. The methylene blue will stain the dead yeast cells a
deep blue but will not stain the living cells.

4. Make a wet mount by placing a small drop of your mixture
of yeast and methylene blue on a microscope slide. Cover the
slide with a coverslip.

5. Observe the mounted slide under the low power of a com-
pound microscope. (Note: Adjust the light so that you can
clearly see both stained and unstained cells.) After focusing,
switch the microscope to high power (400҂ or 1,000҂).

6. Count the live (unstained) yeast cells and the dead (stained)
cells that you see through the microscope. Use the micrometer
ruler, or ask your teacher for the best counting method. Record
the numbers of live cells and dead cells in your data tables.

7. Move the microscope slide slightly, and then make ̈ Stained Yeast Cells These yeast
another count of the number of living and dead cells cells have been stained with methyl-
that you can see. Repeat this step until you have ene blue and magnified 1,000 times
made four counts of the cells on the slide. with a microscope. Methylene blue
gives a deep blue color to dead yeast
8. Calculate and record the average number of live cells but not to live yeast cells.
cells per observation. Record this number in
your data table. Do the same calculation for the
dead cells.

9. Predict how many live and dead cells you
expect to count in the samples from the other
flasks. Record your prediction.

10. Repeat steps 3–8 for each of the flasks to obtain
data that represents the growth of a population
over a 48-hour period.

11. Clean up your work area, and store all lab equip-
ment appropriately. Ask your teacher how to dispose
of the yeast samples and any extra or spilled chemicals.

Analysis

1. Analyzing Data Share your data with the rest of the class.
Calculate and record the class averages for each set of
observations.

2. Constructing Graphs Graph the changes in the average
numbers of live yeast cells and dead yeast cells over time.
Plot the average number of cells per observation on the
y-axis and the time (in hours from start of culture) on
the x-axis.

3. Describing Events Describe the general population changes
you observed in the yeast cultures over time.

Conclusions

4. Evaluating Methods Why were several counts taken and then
averaged for each time period?

5. Evaluating Results Were your predictions of the yeast cell
counts close to the actual average counts? How close were your
predictions relative to the variation among all the samples?

6. Applying Conclusions Did the yeast cell populations appear
to reach a certain carrying capacity? What was the limiting
resource in the experimental environment of the flasks?

Extension

1. Designing Experiments Form a hypothesis about another
factor that might limit the yeast’s population growth, and
explain how you would test this hypothesis.

Chapter 8 Skills Practice Lab 231

WHERE SHOULD THE WOLVES ROAM?

The gray wolf was exterminated the government has not done ̈ A wild wolf is a now rare sight
from much of the northwestern enough to protect wolf popula- in most of the United States. Efforts
United States by the 1920s. tions. Read the following points to reintroduce and protect wolf
Ranchers and federal agents killed of view, and then analyze the populations are controversial.
the animal to protect livestock. The issue for yourself.
Rocky Mountain gray wolf was Hunters point out that hunting
listed as an endangered species in Wolves Should Not Be is an important part of the
1973. Then in the 1980s, the U.S. economies of the western states.
Fish and Wildlife Service began a Reintroduced Also, licensed hunting has become
plan to restore wolf populations in part of the way large parks and
the United States. The agency Some opponents of the reintro- wildlife preserves are managed.
decided to reintroduce wolves into duction plan argue that wolves Hunting is sometimes allowed by
certain areas. Biologists looked for are not truly endangered. Biolo- park and game managers to control
areas where wolves could have gists estimate that hundreds of wildlife populations. Hunting fees
large habitats and enough food. wolves live in Minnesota, and also help fund wildlife management
Three areas were chosen, as shown thousands live in Alaska and efforts, such as habitat improve-
in the figure below. Canada. Because there are large ment and biological studies.
numbers of wolves in the wild,
Between 1995 and 1996, 64 some people feel that wolves Ranchers are among the people
wolves were released in Yellow- should not receive special treat- who most strongly oppose wolf
stone National Park and 34 wolves ment as endangered species. reintroduction. Ranchers worry
were released in central Idaho. The that wolves will kill their live-
original goal was to have breeding Many hunters also oppose the stock. Ranchers argue that they
populations of at least 100 wolves plan to reintroduce wolves. Both cannot afford to lose their live-
in each location by 2002. This goal hunters and wolves hunt for large stock. Even though there is a pro-
has now become reality. game animals such as deer, elk, or gram to pay ranchers for lost
moose. Hunters believe the wolves livestock, the program will last
The wolf reintroduction might create too much competition
efforts remain controversial. Some for the game animals. Some studies
people would prefer that the suggest that populations of game
wolves become extinct. On the animals will decrease if hunted by
other side, some people think that both humans and wolves.

̈ The breeding range of the
gray wolf (far left) has been lost in
most of the United States. The U.S.
government has reintroduced wolves
into parts of Montana, Wyoming,
and Idaho (left).

232 Chapter 8 Points of View

only as long as wolves are clas-
sified as an endangered species.
When there are many wolves
again in the target areas, the
wolf will no longer have endan-
gered status. Ranchers point out
that the payment program will
disappear when it would be
needed most.

Other groups that oppose wolf
reintroduction include groups that
use public lands for activities such
as logging or mining. These
groups worry that protection for
the wolves may lead to the pre-
vention of other uses of land in
the target areas.

Wolves Should Be ̈ The International Wolf Center in Minnesota tries to educate the
public about wolves. The center’s “Wolves and Humans” exhibit is shown here.
Reintroduced
is evidence that most wolves prefer animals that prefer to stay away
A basic argument in favor of wolf to hunt wild animals rather than from people.
reintroduction is that the federal domestic animals. Wolves rarely
government must uphold the law attack livestock when large herds Most wolf supporters admit
by trying to restore wolf popula- of wild game are nearby. In fact, that there are only a few places
tions in the United States. But sup- from 1995 to 1997, fewer than where wolves may live without
porters of wild wolves give other five wolf attacks on livestock were causing problems. Supporters of
reasons too. reported in the United States. the plan believe that the target
areas are places where wolves can
Many environmentalists and Still, some supporters of rein- carry out a natural role without
scientists believe that the reintro- troduction have tried to address causing problems for humans.
duction plan could restore a bal- the concerns of ranchers. One
ance to the Yellowstone ecosystem. group raised money to pay ranch- What Do You Think?
Predation by wolves would keep ers for livestock killed by wolves.
the herds of elk, moose, and deer Other groups conduct studies and Like many plans to protect
from growing too dense and over- educational programs or talk endangered species, the plan
grazing the land. with local landowners. Most wolf to reintroduce wolves causes
supporters are trying to create some people to weigh their
The argument that wolves help reintroduction plans that will own interests against the
control wild herds is like the work for both humans and needs of a single species. Do
argument in favor of hunting. wolves. you feel that the decision is a
Some wolf supporters even say simple one? Can you think of
that licensed hunting of wolves In response to fears that the other ways to look at this
should be allowed. In this way, wolves pose a danger to humans, issue? Explain your answers.
hunters might support the reintro- supporters say this is also unlikely.
duction plans, and populations of There have been no verified
both wolves and game animals attacks on humans by healthy
could be managed. wolves in North America. Wolf
experts insist that wolves are shy
In response to ranchers’ con-
cerns that wolves will attack their
livestock, biologists say that this is
not likely to be a problem. There

Chapter 8 Points of View 233

The Human Population 9C H A P T E R

1 Studying Human

Populations

2 Changing Population

Trends

PRE-READING ACTIVITY

Table Fold
Before you
read this chap-
ter, create the
FoldNote entitled “Table
Fold” described in the
Reading and Study Skills sec-
tion of the Appendix. Label
the columns of the table fold
with “Changes in Human
Population,” and “Effects of
Population Change.” Label
the rows with “Before 1700,”
“From 1700 to 2000,” and
“From 2000 to 2050 and
Beyond.” As you read the
chapter, write examples of
each topic under the
appropriate
column.

China has one of the largest popula-
tions in the world, with more than
1 billion people. However, China’s
population is projected to stop
growing by the year 2050, mostly
because Chinese families are having
fewer children.

234

SECTION 1

Studying Human Populations

The human population of Earth grew faster in the 20th century Objectives
than it ever has before. This rapid growth has led to environ-
mental problems around the globe. We therefore must try to ̈ Describe how the size and growth
understand and predict changes in human populations. rate of the human population has
changed in the last 200 years.
Demography is the study of populations, but most often
refers to the study of human populations. Demographers study ̈ Define four properties that
the historical size and makeup of the populations of countries in scientists use to predict
order to make comparisons and predictions. Demographers also population sizes.
study properties that affect population growth, such as economics
and social structure. Countries are often grouped by demogra- ̈ Make predictions about population
phers into two general categories. Developed countries have trends based on age structure.
higher average incomes, slower population growth, and diverse
industrial economies. Developing countries have lower average ̈ Describe the four stages of the
incomes, simple and agriculture-based economies, and rapid pop- demographic transition.
ulation growth.
̈ Explain why different countries
may be at different stages of the
demographic transition.

Key Terms

The Human Population Over Time demography
age structure
After growing slowly for thousands of years, the human popula- survivorship
tion grew rapidly in the 1800s, as shown in Figure 1. The fertility rate
human population underwent exponential growth, meaning that migration
population growth rates increased during each decade. These life expectancy
increases were mostly due to increases in food production and demographic transition
improvements in hygiene that came with the industrial and sci-
entific revolutions. However, it is unlikely that the Earth can Figure 1 ̈ After growing slowly for
sustain this growth for much longer. thousands of years, the human popu-
lation grew rapidly in the 1800s.
World Population Over Time What caused this change?

Stone Ages Bronze and Middle Modern
Iron Ages Ages Age

8

7 2015
(projected)
Population (in billions) 6
1999

5 1987

4 1974
1960
3 First large Roman Bubonic 1930
Domestication empire(s) Empire plague

2 of plants and 3000 2000 1880
animals

1

0 8000 7000 6000 5000 4000 1000 0 1000 2000
10000 9000 Year

BCE CE

Section 1 Studying Human Populations 235

Rapid Growth— Slow Growth— Zero or Declining Growth—
Least Developed Nations Transitional Nations Most Developed Nations

80+ Males 10 8 6 4 2 0 2 4 6 8 10
Females Percent of population
75–79
70–74 Reproductive
65–69 years

Percent of population surviving Age 60–64
55–59

50–54
45–49
40–44

35–39
30–34

25–29

20–24
15–19

10–14
5–9

0–4

10 8 6 4 2 0 2 4 6 8 10 10 8 6 4 2 0 2 4 6 8 10
Percent of population Percent of population

Figure 2 ̈ Age-Structure Forecasting Population Size
Diagrams These graphs allow
demographers to compare the distri- Will your community need more schools in the next 20 years, or
bution of ages and sexes in a popula- will it need more retirement communities? Will people move in
tion. Each graph shows a typical and create demand for more roads and utility services?
shape for a population with a partic- Demographers look at many properties of populations to predict
ular rate of growth. Note that people such changes. Population predictions are often inaccurate, how-
between 15 and 44 years of age are ever, because human behavior can change suddenly.
most likely to produce children.
Age Structure Demographers can make many predictions based
Typical Survivorship Curves on age structure —the distribution of ages in a specific population
100 at a certain time. For example, if a population has more young
people than older people, the population size will likely increase
Type I as the young people grow up and have children. Age structure
80 can be graphed in a population pyramid, a type of double-sided
bar graph like those shown in Figure 2. The figure shows typical
60 Type II age structures for countries that have different rates of growth.
Countries that have high rates of growth usually have more
40 young people than older people. Countries that have slow growth
or no growth usually have an even distribution of ages.
20
Type III Survivorship Another way to predict population trends is to
study survivorship. Survivorship is the percentage of members of
0 a group that are likely to survive to any given age. To predict
survivorship, a demographer studies a group of people born at
Time the same time and notes when each person dies. The results plot-
Figure 3 ̈ Survivorship curves show ted on a graph might look like one of the types of survivorship
how much of the population survives curves in Figure 3. Wealthy developed countries such as Japan
to a given age. Both Type I and Type and Germany currently have a Type I survivorship curve because
III survivorship may result in popula- most people live to be very old. Type II populations have a simi-
tions that remain the same size or lar death rate at all ages. Type III survivorship is the pattern in
grow slowly. very poor human populations in which many children die.

■✓● Reading Check How can a population pyramid help demographers

predict changes in a population over time? (See the Appendix for

answers to Reading Checks.)

236 Chapter 9 The Human Population

Total fertility rate Baby boom Baby bust

4.0

Figure 4 ̈ The total fertility rate in
the United States went through
3.5 many changes from 1900 to 2000.
The baby boom was a period of high
3.0 fertility rates, and the baby bust was a
period of decreasing fertility.
Replacement
2.5 level

2.0

1.5 1930 1940 1950 1960 1970 1980 1990 2000
1920 Year

Fertility Rates The number of babies born each year per 1,000 MATHPRACTICE
women in a population is called the fertility rate. Demographers
also calculate the total fertility rate, or the average number of Extending the Equation
children a woman gives birth to in her lifetime. for Population Change
The following equation is a
A graph of historical total fertility rates for the United States is simple way to calculate the change
shown in Figure 4. In 1972, the total fertility rate dropped below in a population over a period
replacement level for the first time in U.S. history. Replacement level of time:
is the average number of children each parent must have in order to
“replace” themselves in the population. This number is about 2.1, change in = (births Ҁ deaths)
or slightly more than 2, because not all children born will survive population
and reproduce.
However, this equation does not
Total fertility rates in the United States remained below replace- account for changes due to migra-
ment level for most of the 1990s. However, the population contin- tion. Rewrite the equation to
ued to grow, as shown in Figure 5. One reason for this growth was include immigration and emigration.
that the children of the baby boom grew up and had children.
Next, create an example word
Migration Another reason the population continued to grow was problem that would require the
that immigration increased. The movement of individuals use of this new equation. Trade
between areas is called migration. Movement into an area is problems with a classmate, and
immigration and movement out of an area is emigration. try to solve the classmate’s new
Migration between and within countries is a significant part of word problem.
population change. The populations of many developed countries
might be decreasing if not for immigration.

Number added to 35 Figure 5 ̈ The population of the
population (in millions) 30 Increase due to immigration United States has continued to grow
in the last century because of births
Increase due to births as well as immigration.
25
1990–2000
20
Section 1 Studying Human Populations 237
15

10

5

0 1960–1970 1970–1980 1980–1990
1950–1960 Decade

Source: U.S. Census Bureau.

Figure 6 ̈ Preventive medicine, Declining Death Rates
sanitation, and better nutrition have
increased life expectancy in many The dramatic increase in Earth’s human population in the last
parts of the world. 200 years has happened because death rates have declined more
rapidly than birth rates. Death rates have declined mainly because
more people now have access to adequate food, clean water, and
safe sewage disposal. The discovery of vaccines in the 20th cen-
tury also contributed to declining death rates, especially among
infants and children. These factors are shown in Figure 6.

Figure 7 ̈ Since 1900, average life Life Expectancy The average number of years members of a pop-
expectancy has increased worldwide ulation are likely to live is their life expectancy. Life expectancy is
(red line), although it remains lower most affected by infant mortality, the death rate of infants less than
in less developed countries (blue and a year old. In 1900, worldwide life expectancy was about 40 years
purple lines). and the infant mortality rate was very high. By 2000, the rate of
infant mortality was less than one-third of the rate in 1900. The
Average Life Expectancy graph in Figure 7 shows that average life expectancy has increased
by Region to more than 67 years worldwide. For people in many developed
countries, life expectancy is 80 years or more.
90
80 More developed regions Expensive medical care is not needed to prevent infant deaths.
The infant mortality rate differs greatly among countries that have
Age 70 the same average income. Instead, infant health is more affected
60 World by the parents’ access to education, food, fuel, and clean water.
Babies need to be fed well and kept clean and warm. If these basic
50 needs are met, most children will have a good chance of surviving.

40 Meanwhile, new threats to life expectancy arise as popula-
Less developed regions tions become denser. Contagious diseases such as AIDS and
tuberculosis are a growing concern in a world where such dis-
30 Least developed regions eases can spread quickly. Life expectancy in many Southern
20 African countries has been reduced in recent decades due to the
AIDS epidemic.
10

0 1975 1995 2015
1955

Year (projected)

Source: UN Population Division.

238 Chapter 9 The Human Population

The Demographic Transition www.scilinks.org

In most developed countries, populations have stopped growing. Topic: Demographic
How can populations quadruple in one century, then stop grow- Transition
ing or shrink in the next century? The demographic transition is
a model that describes how economic and social changes affect Code: HE80386
population growth rates. The model is based on observations
of the histories of many developed countries. The graph in Ecofact
Figure 8 compares trends in birth rates, death rates, and popu-
lation sizes during the four stages of the transition. The Population Clock The
Earth’s human population is
Stages of the Transition In the first stage of the demographic increasing by 2.4 people each sec-
transition, a society is in a preindustrial condition. The birth rate ond, which accounts for births and
and the death rate are both at high levels and the population size deaths. This means Earth gains
is stable. Most of the world was in this condition until about over 200,000 people per day, or
1700, when the scientific and industrial revolutions began. over 75 million per year.

In the second stage, a population explosion occurs. Death Figure 8 ̈ The four stages of the
rates decline as hygiene, nutrition, and education improve. But demographic transition are shown
birth rates remain high, so the population grows very fast. During here from left to right. Note the
this stage, the population can double in less than 30 years. changes in population size with
changing birth and death rates.
In the third stage of the demographic transition, population Do you think that all countries will
growth slows because the birth rate decreases. As the birth fit this pattern?
rate becomes close to the death rate, the population size stabi-
lizes. However, the population is much larger than before the Stage 4
demographic transition. In most countries that have passed Postindustrial
through the transition, the population quadrupled during the
20th century. Large

In the fourth stage, the birth rate drops below replacement
level, so the size of the population begins to decrease. It has taken
from one to three generations for the demographic transition to
occur in most developed countries.

■✓● Reading Check Which stage of the demographic transition is char-

acterized by a high birth rate and a declining death rate?

Stage 1 Stage 2 Stage 3
Preindustrial Transitional Industrial

High

Birth rate and death rate Population size
Population size
Birth rate

Replacement level birth rate

Low Death rate Small
Low
Increasing Very high Decreasing Low Zero Negative
growth rate growth rate growth rate growth rate growth rate growth rate growth rate

Time

Section 1 Studying Human Populations 239

Connection to Biology Women and Fertility The factors most clearly related to a
decline in birth rates are increasing education and economic inde-
Female Influence Females have pendence for women. In the demographic transition model, the
the primary influence over repro- lower death rate of the second stage is usually the result of
ductive rates in most species of increased levels of education. Educated women find that they do
animals, because they invest not need to bear as many children to ensure that some will sur-
more energy in reproduction vive. Also, the women may learn family planning techniques.
than males do. Females usually They are able to contribute to their family’s increasing prosperity
produce and lay eggs, carry the by working, while spending less energy bearing and caring for
fetus, give birth, and care for the children. Some countries that want to reduce birth rates have placed
young offspring. The time and a priority on the education of females, as shown in Figure 9.
resources a female must invest in
each successful offspring is usu- Large families are valuable in communities in which children
ally greater than the energy a work or take care of older family members. But as countries
male must invest. modernize, parents are more likely to work away from home. If
parents must pay for child care, children may become a financial
www.scilinks.org burden rather than an asset. The elderly will not need the support
of their children if pensions are available. All of these reasons
Topic: Human contribute to lower birth rates. Today, the total fertility rate in
Demographics developed countries is about 1.6 children per woman, while in
developing countries, the rate is about 3.1 children per woman.
Code: HE80767

Figure 9 ̈ These women in Bolivia
are learning to read. Many countries
include the education of women in
development efforts.

S E C T I O N 1 Review

1. Describe how the size and growth rate of the CRITICAL THINKING
human population has changed in the last 200 years.
5. Analyzing Relationships Read the description of
2. Define four properties that scientists use to predict life expectancy in this section. Explain why the oldest
population sizes. people in a population may be much older than the
average life expectancy. READING SKILLS
3. Explain what we can predict about a population’s
likely growth rates based on its current age structure. 6. Evaluating Theories Do you think that all coun-
tries will follow the pattern of the demographic tran-
4. Describe the four stages of the demographic transition. sition? Explain your answer.

240 Chapter 9 The Human Population

SECTION 2

Changing Population Trends

Some countries have followed the model of the demographic Objectives
transition—they have reached large and stable population sizes
and have increased life expectancies. But throughout history, and ̈ Describe three problems caused by
currently in many parts of the world, populations that have high rapid human population growth.
rates of growth create environmental problems. A rapidly grow-
ing population uses resources at an increased rate and can over- ̈ Compare population growth prob-
whelm the infrastructure of a community. Infrastructure is the lems in more-developed countries
basic facilities and services that support a community, such as and less developed countries.
public water supplies, sewer lines, power plants, roads, subways,
schools, and hospitals. The symptoms of overwhelming popula- ̈ Analyze strategies countries may
tion growth include suburban sprawl, overcrowded schools, pol- use to reduce their population
luted rivers, barren land, and inadequate housing, as shown in growth.
Figure 10. You may have seen some of these problems in your
community. ̈ Describe worldwide population
projections into the next century.
Problems of Rapid Growth
Key Terms
People cannot live without sources of clean water, fuel, and land
that can be farmed to produce food. A rapidly growing popula- infrastructure
tion can use resources faster than the environment can renew arable land
them, unless resources come from elsewhere. Standards of living urbanization
decline when wood is removed from local forests faster than it least developed countries
can grow back, or when wastes overwhelm local water sources.
Vegetation, water, and land are the resources most critically Geofact
affected by rapid growth.
Land Area per Person If each
person alive on Earth in the year
2000 was given an equal portion
of existing surface land, each per-
son would get about 7.3 acres
(0.025 km2, or about four football
fields). In the year 2050, each per-
son might get 4.8 acres of land
(0.016 km2, or about two and a
half football fields).

Figure 10 ̈ Rapid population
growth can put pressure on water
sources, land, and materials used for
fuel or shelter. The makeshift housing
shown here is one consequence of
unmanaged growth.

Section 2 Changing Population Trends 241

Figure 11 ̈ Gathering fuel is part
of daily survival in many developing
countries. If there is not enough
wood to use for fuel, people may
have to burn crop residue. This can
lead to soil erosion and lower agri-
cultural productivity.

Spider Map A Shortage of Fuelwood Women in Myanmar gathering fire-
Create the wood are shown in Figure 11. In many of the poorest countries,
Graphic Organizer entitled wood is the main fuel source. When populations are stable, peo-
“Spider Map” described in the ple use fallen tree limbs for fuel, which does not harm the trees.
Appendix. Label the circle When populations grow rapidly, deadwood does not accumulate
“Problems of Rapid Population fast enough to provide enough fuel. People begin to cut down liv-
Growth.” Create a leg for each ing trees. Parts of Africa, Asia, and India have been cleared of
problem of rapid population vegetation by people collecting fuelwood.
growth. Then, fill in the
map with details about A supply of fuel ensures that a person can boil water and cook
each problem of rapid food. In many parts of the world, water taken directly from wells
population growth. or public supplies is not safe to drink because it contains water-
borne parasites or other diseases. The water can be sterilized by
Figure 12 ̈ This woman is washing boiling it, but fuel is needed to do so. Also, food is often unsafe or
clothes in the Rio Grande on the harder to digest unless it is cooked. Without enough fuelwood,
U.S.-Mexico border. In areas that many people suffer from disease and malnutrition.
have no sewage or water treatment
systems, people may use the same Unsafe Water In places that lack
water supply for drinking, bathing, infrastructure, the local water supply
washing, and sewage disposal. may be used not only for drinking
and washing but also for sewage dis-
242 posal. As a result, the water supply
becomes a breeding ground for
organisms that cause diseases such
as dysentery, typhoid, and cholera.

Many cities have populations
that are doubling every 15 years, and
water systems cannot be expanded fast
enough to keep up with this growth.
In 2001, over 1 billion people world-
wide lacked safe drinking water and
more than 3 million died of diseases
that were spread through water. The
Rio Grande, shown in Figure 12, is
one example of an unsafe water source
used by many people.

Lima, Peru, is another example of an area with unsafe water. FIELD ACTIVITY
More than half of the population of Lima is housed in shanty-
towns that have no plumbing. The bacteria that cause cholera Does Your Local Area Have
thrived in Lima’s unmanaged water sources in 1991. In that year, Population Pressures? Take an
Lima’s population suffered the first epidemic of cholera that had informal survey of your commu-
occurred in the Western Hemisphere in 75 years. nity’s population trends. Gather
information by taking a walk,
Impacts on Land People prefer to live where they have easy reading the local newspaper, or by
access to resources. Growing populations may have a shortage of contacting your local government
arable land, which is land that can be used to grow crops. or chamber of commerce offices.
Growing populations also make trade-offs between competing
uses for land such as agriculture, housing, or natural habitats. Try to answer the following
questions:
For example, Egypt’s population of 73 million is growing at • Is your local population grow-
2 percent per year. For food and exportable products, Egypt
depends on farming within the Nile River valley, shown in ing or shrinking? How much
Figure 13. Most of the country is desert, and less than 4 percent change is due to migration?
of Egypt’s land is arable. However, the Nile River valley is also
where most Egyptians live. Egyptians continue to build housing • What growth-related problems
on what was once farmland, which reduces Egypt’s available are citizens and government
arable land. planners aware of?

Much of the world’s population is undergoing urbanization, the • What solutions are being pro-
movement of people from rural areas to cities. In the United States, posed or debated?
people often find work in the cities but move into suburban areas
around the cities. This suburban sprawl leads to traffic jams, inade- Record your results in your
quate infrastructure, and the reduction of land for farms and EcoLog.
wildlife habitat. Meanwhile, housing within cities becomes more
costly, more dense, and in shorter supply. Figure 13 ̈ Egypt’s population is
mostly crowded into the narrow Nile
■✓● Reading Check How has rapid population growth affected arable River valley. The United States has
more arable land, but suburban
land in Egypt? sprawl (left) creates many problems.

Nile River valley
243

Connection to Law A Demographically Diverse World

International Development As you have seen, demographers may categorize countries as
The United Nations (UN) has an either developed or developing. However, demographers may pre-
important role in understanding fer the terms more developed and less developed to describe
and assisting the development of countries or regions, because the reality of development is com-
nations. The UN holds confer- plex and politically sensitive.
ences, publishes research, creates
treaties, manages international Not every country in the world is progressing through each
programs, and dispenses funds. stage of the demographic transition according to the model. Some
countries now have modern industries, but incomes remain low. A
The UN also creates formal few countries have achieved stable and educated populations with
designations, such as least devel- little industrialization. Some countries seem to remain in the sec-
oped countries. Demographers, ond stage of the model. These countries have rapid population
foreign aid programs, and inter- growth, but are unable to make enough educational and economic
national treaties may use these gains to reduce the birth rate and move into the third stage.
designations.
In recent years, the international community has begun to
focus on the least developed countries. These countries show few
signs of development and in some cases have increasing death
rates, while birth rates remain high. Least developed countries are
officially identified by the United Nations. These countries may
be given priority for foreign aid and development programs to
address their population and environmental problems.

Thailand’s Population Challenges

Population growth is a major con- ̈ Bangkok, Thailand is one of the most crowded and polluted cities in
cern for many developing coun- the world. However, population growth is slowing in Thailand, and some
tries. But the options are limited environmental problems are starting to be solved.
for a country that has a poor
economy and growing demands
for limited resources. Thailand is
one country that has effectively
and purposefully slowed its popu-
lation growth.

Around 1970, Thailand’s popu-
lation was growing at a rate of more
than 3 percent per year, and the
average Thai family had 6.4 chil-
dren. The country had increasing
environmental problems, such as air
pollution in major cities and unsafe
water supplies. Thailand’s emissions
of carbon dioxide from burning fos-
sil fuels almost doubled between
1990 and 1997. In Thailand’s capi-
tal, Bangkok, one-ninth of residents

244 Chapter 9 The Human Population

9,000 Figure 14 ̈ Growth rates vary
in different parts of the world.
World population (in millions) 8,000 Asia Which regions will contribute the
7,000 Africa most growth?
6,000 Latin America
5,000 Europe www.scilinks.org
4,000 Northern America
(U.S., Canada, Topic: Developed and
Greenland) Developing Countries
Code: HE80397
3,000

2,000

1,000

0 1800 1850 1900 1950 1999 2050
1750 Year

(projected)

Source: UN Population Division.

Growth rates for different parts of the world are shown in
Figure 14. Populations are relatively stable in Europe, the United
States, Canada, Russia, South Korea, Thailand, China, Japan,
Australia, and New Zealand. In contrast, populations are still
growing rapidly in less developed regions. Most of the world’s
population is now within Asia.

Thailand’s Population Strategies

• improved healthcare for mothers • economic incentives such as How did Thailand make such
and children building loans for families major changes with limited
who participated in family resources? Demographers believe
• openness of the people, govern- planning programs the changes are due to the combi-
ment, and community leaders to nation of strategies shown in
changing social traditions • creative family-planning the table at left.
programs promoted by
• cooperation of private and popular government leaders CRITICAL THINKING
nonprofit organizations with
the government • high literacy rates of women 1. Applying Ideas For what rea-
(80 percent in 1980 and sons could Thailand be described as
• increases in women’s rights and 94 percent in 2000) a developing country in the 1970s?
ability to earn income In what ways was it able to change?

have respiratory problems, and to parents who have fewer chil- 2. Expressing Viewpoints Do
many people die of waterborne dis- dren. Fifteen years later, the coun- you approve of all of the strategies
eases each year. try’s population growth rate had that the government of Thailand
been cut to about 1.6 percent. employed in order to reduce their
In 1971, Thailand’s govern- By 2000, the growth rate had population growth? Do the goals
ment adopted a policy to reduce fallen to 1.1 percent and the justify the strategies they used?
Thailand’s population growth. age structure was more evenly Write a persuasive paragraph to
The policy included increased distributed. These changes also defend your opinion. WRITING SKILLS
education for women, greater reflected a decline in the infant
access to healthcare and contra- mortality rate.
ceptives, and economic incentives

Section 2 Changing Population Trends 245

Figure 15 ̈ China has implemented
a long campaign to reduce birth
rates. Strategies have included
economic rewards for single-child
families, and advertising such as the
billboard shown here.

Table 1 ̄

ICPD Goals for 2015

• Provide universal access to a Managing Development and Population Growth
full range of safe and reliable
family-planning methods and Humans throughout history have witnessed the negative effects of
related reproductive health population growth. Today, less developed countries know that
services. continued population growth can limit their economic develop-
ment. The governments of some countries, such as China,
• Reduce infant mortality rates to Thailand, and India, have tried to reduce birth rates using public
below 35 infant deaths per advertising, as shown in Figure 15, family planning programs,
1,000 live births and mortality economic incentives, or legal punishments.
rates of children under five
years old to below 45 deaths In 1994, the United Nations held the International
per 1,000 live births. Conference on Population and Development (ICPD). This confer-
ence involved debates about the relationships between popula-
• Close the gap in maternal tion, development, and environment. Table 1 shows the main
mortality between developing goals that resulted from the conference. Many countries favor
and developed countries. stabilizing population growth through investments in develop-
Achieve a maternal mortality ment, especially through improvements in women’s status. In fact,
rate below 60 deaths per worldwide fertility rates are dropping, as shown in Figure 16.
100,000 live births.
■✓● Reading Check What are two examples of strategies that a govern-
• Increase life expectancy at birth
to more than 75 years. In ment might use to try to limit population growth?
countries with the highest
mortality, increase life Total fertility (children per woman) 7 Least developed regions
expectancy at birth to more 6 Less developed regions
than 70 years. 5

• Achieve universal access to and World
completion of primary educa- 4
tion. Ensure the widest and ear-
liest possible access by girls and
women to secondary and
higher levels of education.

Source: UN Population Fund.

3

Figure 16 ̈ Worldwide Trends in 2
Fertility Most countries’ fertility More developed regions
rates are dropping toward replace-
ment level. 1

246 Chapter 9 The Human Population 0 1980 1985 1990 1995 2000 2005 2010
1955 1960 1965 1970 1975 Year (projected)

Source: UN Population Division.

Growth Is Slowing QuickLAB

The human population of the world is now more than 6 billion Estimating Fertility Rates
and is still increasing. The worldwide population growth rate
peaked at about 87 million people per year between 1985 and Procedure
1990. In contrast, the population grew by only 81 million people 1. Your goal is to estimate the
per year from 1990 to 1995.
average fertility rate of the
Fertility rates have declined since about 1970 in both more- mothers of students in your
developed and less developed regions. However, rates are still school. Design and conduct a
much higher in less developed regions. Demographers predict that quick survey of other students
this trend will continue and that worldwide population growth in the school.
will be slower in this century than in the last century. If current 2. Create one or two survey ques-
trends continue, most countries will have replacement level fertil- tions that will collect the
ity rates by 2050. If so, world population growth would even- needed information. Be sure
tually stop. that the questions are sensitive
to personal differences and are
Projections to 2050 United Nations projections of world popula- not judgmental.
tion growth to 2050 are shown in Figure 17. The medium-growth 3. Devise a method to make the
line assumes that worldwide fertility rates will decline to replace- survey anonymous. You might
ment level by 2050. The high- and low-growth lines would result simply pass out a questionnaire
from higher or lower fertility rates. Most demographers predict the to another class.
medium growth rate and a world population of 9 billion in 2050. 4. Get your teacher’s approval for
your survey questions and
World population (in billions) World Population Projection for Different Growth Rates method, and then conduct
12 your survey.
Analysis
High growth rate 1. Analyze your results, and pre-
pare a short summary of your
10 Medium growth rate findings.

8 Figure 17 ̈ Current fertility trends
will result in a world population of
6 about 9 billion in 2050 (middle line).
Low growth rate Economic or political changes could
lead to higher or lower numbers.
4

2

0 2000 2050
1950 Year (projected)

Source: UN Population Division.

S E C T I O N 2 Review

1. Describe three problems caused by rapid human CRITICAL THINKING
population growth. 4. Analyzing a Viewpoint Write a comparison of the

2. Compare population growth in more-developed pros and cons of the strategies nations have used to
countries to population growth in less developed reduce population growth. WRITING SKILLS
countries.
5. Analyzing Relationships Do you think that simply
3. Describe worldwide population projections for the changing birth rates will cause a nation to undergo
next 50 years. further development?

Section 2 Changing Population Trends 247

9C H A P T E R Highlights

1 Studying Human Populations Key Terms Main Ideas

demography, 235 ̈ Human population growth has accelerated
age structure, 236 in the last few centuries. The main reasons for
survivorship, 236 this growth were improvements in hygiene and
fertility rate, 237 increases in food production, which accom-
migration, 237 panied the industrial and scientific revolutions.
life expectancy, 238
demographic ̈ Demographers try to predict population
trends using data such as age structure, sur-
transition, 239 vivorship, fertility rates, migration, and life
expectancy.

̈ In the demographic transition model, coun-
tries progress through four stages of change in
birth rates, death rates, and population size.

2 Changing Population Trends infrastructure, 241 ̈ When a growing population uses resources
arable land, 243 faster than they can be renewed, the resources
urbanization, 243 most critically affected are fuelwood, water,
least developed and arable land.

countries, 244 ̈ In this century, countries may be labeled
more developed or less developed. Not all
countries are going through the demographic
transition in the same way that the more-
developed countries did.

̈ Some countries attempt to reduce birth rates
directly through public advertising, family plan-
ning programs, economic incentives, or legal
punishments for their citizens.

248 Chapter 9 Highlights

9C H A P T E R Review

Using Key Terms 11. Which countries have Type I survivorship?
a. the most developed countries
Use each of the following terms in a separate b. the least developed countries
sentence. c. countries in the second stage of the demo-
graphic transition
1. demography d. countries in the first stage of the demo-
graphic transition
2. demographic transition
12. The demographic transition is a(n)
3. infrastructure a. untested hypothesis.
b. natural law.
4. least developed countries c. model based on observed patterns.
d. international law.
For each pair of terms, explain how the meanings
of the terms differ. 13. A country in the second stage of the demo-
graphic transition may have all of the fol-
5. age structure and survivorship lowing except
a. increasing agricultural production.
6. infant mortality and life expectancy b. improving healthcare and education.
c. decreasing population size.
7. death rate and fertility rate d. decreasing death rates.

8. urbanization and migration 14. Which of the following resources is likely to
be impacted the most by a rapidly growing
STUDY TIP population?
a. clothing
Quantitative Terms Look for key terms in the b. food
graphs in this chapter. In your EcoLog, copy the c. housing
graphs and write brief descriptions of how key d. water
terms may relate to the graphs and to other key
terms. For example, copy Figure 3, and write “High 15. Which of the following diseases is often
infant mortality results in low life expectancy and spread through unsafe public water sources?
Type III survivorship.” a. dysentery
b. flu
Understanding Key Ideas c. chickenpox
d. AIDS
9. Age structure data include all of the follow-
ing except 16. Which of the following uses of wood is the
a. the number of members of a population most important for basic human needs?
who are between 5 and 11 years old. a. heating the home
b. the ratio of males to females in a b. boiling water
population. c. making tools
c. the amount of population change due to d. building shelter
immigration or emigration.
d. the ratio of older people to younger people 17. In this century, the world population is
in a population. likely to
a. remain the same.
10. Human population growth accelerated in b. continue to grow exponentially.
recent centuries mostly because of c. decline rapidly because fertility rates are
a. the bubonic plague. already below replacement level.
b. better hygiene and food. d. stabilize after fertility rates fall below
c. the discovery of electricity. replacement level.
d. improved efficiency of fuel use.

Chapter 9 Review 249

9C H A P T E R Review

Short Answer Concept Mapping ?
??
18. What are the main reasons that life
expectancy has increased worldwide? 27. Use the following terms to create a concept
map: rapid human population growth,
19. How does the age structure of a population demographic transition, survivorship, fertil-
help predict future population growth? ity rate, fuelwood, water, and land.

20. What is the relationship between education Critical Thinking
and fertility rates in a human population?
28. Analyzing Predictions Why are human pop-
21. Which properties of a population change ulation trends difficult to predict? Describe
during the demographic transition? an example of an event that would change
most demographic predictions.
22. Which key resources are impacted the most by
rapidly growing populations? 29. Analyzing Methods In what ways does the
study of human populations differ from the
23. Which regions of the world are generally study of wildlife ecology?
more developed? less developed?
30. Identifying Relationships What other fac-
Interpreting Graphics tors, besides those already mentioned, might
have an effect on fertility rates in a given
The graph below shows each region’s contribu- population?
tion to world population growth. Use the graph
to answer questions 24–26. 31. Evaluating Theories Write an evaluation of
the demographic transition as a theory of
24. Which region(s) are projected to increase in how populations will develop. How useful is
population size? the demographic transition model in predict-
ing the future? What assumptions are made
25. Which region(s) are projected to decline in by the theory? What criticisms could be
population size? made of the theory? WRITING SKILLS

26. Can you assume that all the countries within Cross-Disciplinary Connection
each region have the same growth patterns?
Explain your answer. 32. Careers Demographers are employed by
many kinds of organizations including
World Population Growth by Region governments, health organizations, and
insurance companies. How can their skills be
9,000 useful to each of these organizations?

World population (in millions) 8,000 Asia 33. Social Studies Find out the demographic his-
7,000 Africa tory, for the last 100 years, of a developing
6,000 Latin America country of your choice. Explain how closely
5,000 Europe this country’s pattern of development follows
4,000 Northern America the demographic transition model.
(U.S., Canada,
Greenland)

3,000

2,000

1,000 Portfolio Project

0 34. Research Demographic Trends Look up
population statistics for your local city,
1750 1800 1850 1900 1950 1999 2050 county, or state. Read and take notes about
recent demographic trends and predictions
Year (projected) for the next few decades. Make a summary
of your findings. READING SKILLS

250 Chapter 9 Review

Total fertility rateMATH SKILLS READING SKILLS

Use the graph below to answer questions 35–37. Read the passage below, and then answer
the questions that follow.
35. Analyzing Data At which times did the fer-
tility rate change most drastically in the Excerpt from UN Population Fund, The State
United States? of World Population 2001, 2001.

36. Graphing Data Sketch a copy of the graph Worldwide, women have primary responsi-
below. Smooth the bumps to give an idea of bility for rearing children and ensuring suf-
general trends. ficient resources to meet their needs. In the
rural areas of developing countries, women
37. Drawing Conclusions On your new graph, are also the main managers of essential
draw a second line to show the changes in household resources like clean water, fuel for
population size that you would predict to cooking and heating, and fodder for domes-
result from the given fertility rates over time. tic animals.

4.0 Women make up more than half of the
world’s agricultural workforce. They grow
3.5 crops for the home and market and often
produce most staple crops. In the world’s
3.0 poorest countries, women head almost a
Replacement quarter of rural households.

2.5 level However, although women have the pri-
mary responsibility for managing resources,
2.0 they usually do not have control. National
law or local customs often deny women the
1.5 right to secure title or inherit land, which
1920 1930 1940 1950 1960 1970 1980 1990 2000 means they have no collateral to raise credit
Year and improve their conditions.

WRITING SKILLS Women often lack rights in other aspects
of their lives, reinforcing gender inequalities.
38. Writing Persuasively Write an opinion arti- High fertility and large families are still a fea-
cle for a newspaper or magazine. Argue ture of rural life, though the rationale has long
either for or against a policy related to immi- since passed. In part, this reflects women’s
gration or family planning. lack of choice in the matter.

39. Writing Using Research Look up recent cen- 1. Which of the following are not cited in
sus data from your city, county, or state. the passage as major responsibilities of
Write a paragraph that describes the major women?
demographic trends of the last few years. a. management of household resources
b. agricultural work
c. government leadership
d. rearing children

2. The passage implies that improving
women’s rights would lead to
a. the ability of women to earn more money.
b. increased availability of fuel.
c. poorer rural households.
d. larger families.

Chapter 9 Review 251

9C H A P T E R Standardized Test Prep

Understanding Concepts Reading Skills

Directions (1–4): For each question, write on a Directions (7–8): Read the passage below. Then
separate sheet of paper the letter of the correct answer the questions.
answer.
Growing populations often make trade-offs
1 How did the human population change in between competing uses for land such as
agriculture, housing, or natural habitats.
the last 200 years? Much of the world’s population is undergoing
A. increased at a decelerated rate urbanization, the movement of people from
B. increased at an accelerated rate rural areas to cities. In the United States, many
C. decreased at a decelerated rate cities are becoming large metropolitan areas.
D. decreased at an accelerated rate People often work in the cities but live in
nearby suburbs. This leads to suburban
2 Which of the following has the most effect sprawl, traffic jams, inadequate infrastructure,
and the reduction of land for farms, ranches,
on the infant mortality rate? and wildlife habitat.
F. Parents have a college education.
G. Parents live in a quiet suburban area. 7 How does urbanization affect agriculture?
H. Parents are in the higher income brackets.
I. Parents keep a baby fed, clean and warm. A. It reduces land available for crops.
B. It reduces land available for housing.
3 Why have populations in most developed C. It reduces the safety of the water supply.
D. It reduces the variety of foodstuffs.
countries stopped growing?
A. In most developed countries, immigration 8 Give an example of a situation where a

has decreased and emigration increased. population must decide how to use limited
B. In most developed countries, contagious land resources, and the foreseeable effect of
that decision.
diseases have reduced life expectancies.
C. In most developed countries, birth rates Directions (9): Read the passage below. Then
answer the question.
have decreased to a level close to the
death rate. The demographic transition model describes
D. In most developed countries, industrial how population changes can occur. The model
development that created progress has is based on observations of the history of
moved to less developed countries. many developed countries. The theory behind
the model is that industrial development
4 What is the term for the average number causes economic and social progress that then
affects population growth rates.
of years people in a population are likely
to live? 9 What is the basis for the demographic
F. age structure
G. demographic transition transition model?
H. life expectancy F. the industrial development of developed
I. migration pattern
countries
Directions (5–6): For each question, write a short G. economic and social progress in develop-
response.
ing countries
5 During a period of population growth, the H. observations of the history of all

resources most critically affected are fuel- countries
wood, water, and arable land. Explain how I. observations of the history of many
the supply of fuelwood is affected by human
population growth. developed countries

6 Describe two of the factors used to predict

human population size.

252 Chapter 9 Standardized Test Prep

Interpreting Graphics

Directions (10–12): For each question below, record the correct answer on
a separate sheet of paper.

The graph below shows population projections for the world at different
growth rates. Use this graph to answer questions 10 through 12.

World population (in billions) World Population Projection For Different Growth Rates

12
High growth rate

10
Medium growth rate

8

6
Low growth rate

4

2

0 2000 2050
1950 Year (projected)

0 Which of the following can be inferred from the medium growth rate Test

predicted? When solving a math
A. Migration will no longer add to the overall population problem, be sure to
examine the units
growth. involved closely.
B. Life expectancy will decrease more rapidly in less-developed

countries.
C. Most countries will have reached replacement level fertility rates

by 2050.
D. More-developed countries will have greater growth than

less-developed countries.

q What does the chart project as the most likely outcome for the world

population?
F. It will be 12 billion in 2050.
G. It will double by the year 2050.
H. It will increase by 25% by the year 2050.
I. It will be between 8 and 11 billion in 2050.

w By how many billions of people did the population increase between

1950 and 2005?

A. 2 C. 4

B. 3 D. 5

Chapter 9 Standardized Test Prep 253

9C H A P T E R Skills Practice Lab: MATH/GRAPHING

Objectives How Will Our Population Grow?

̈ USING SCIENTIFIC METHODS Predict If you were a demographer, you might be asked to determine how
which variable has a greater effect a population is likely to change in the future. You have learned
on population growth rates. that the rate of population growth is affected by both the number
of children per family and the age at which people have children.
̈ Calculate changes for a given But which factor has a greater effect? To explore this question,
population over a 50-year period. you will use age-structure diagrams—also called population pyra-
mids—such as the one shown below.
̈ Graph the resulting population’s
age structure by creating a popula- Procedure
tion pyramid.
1. In this lab you will calculate future population trends for an
̈ Compare the effects of fertility imaginary city. To compare how fertility variables may
variables on population growth affect population growth, each group of students will test
rates. the effects of different assumptions. Assume the following
about the population of this city:
Materials
Assumptions About the Population
calculator or computer
colored pencils or markers • Half the population is male and half is female.
graph paper
notebook • Every woman will have all of her children during a given five-
pen or pencil year period of her life.
ruler
• Everyone who is born will live to the age of 85 and then die.

• No one will move into or out of the city.

2. Your teacher will divide the class into four groups. Each
group will project population growth using the following
assumptions:

̈ Age Structure You will make an Assumptions About the Women in the Population
age-structure diagram, such as this
graph of the U.S. population in 2000. Each woman gives While in the age
birth to range of
United States, 2000 Group

80+ Males Females A 5 children 15–19
75–79 B 5 children 25–29
Age 70–74 C 2 children 15–19
65–69 D 2 children 25–29
60–64
55–59 3. Predict which of the four groups will have the greatest popu-
50–54 lation growth in 50 years. Write down the order you would
45–49 predict for the relative size of the groups from largest popu-
40–44 lation to smallest population.
35–39
30–34
25–29
20–24
15–19
10–14

5–9
0–4

12 8 4 0 4 8 12
Population (in millions)

254 Chapter 9 Skills Practice Lab

4. The table at right shows the population of our imaginary city Population in Each Age
for the year 2000. Use the data in the table to make an age- Group, 2000–2050
structure diagram (population pyramid) for the city. Use the
example diagram at left to help you. Age 2000 2005 2010

5. Make a table similar to the one shown at right. Add columns 80+ 100 DO NOT WRITE IN THIS BOOK
for the years 2005, 2010, and for every fifth year until the
year 2050. 75–79 500

6. Calculate the number of 0- to 4-year-olds in the year 2005. 70–74 600
To do this, first determine how many women will have chil-
dren between 2000 and 2005. Remember that half of the 65–69 700
population in each age group is female, and that members of
the population will reproduce at specific ages. Multiply the 60–64 800
number of child-bearing women by the number of children
that each woman will have. For example, Group A will have 55–59 900
12,500 new births by 2005.
50–54 1,000
7. Fill in the entire column for the year 2005. Determine the
number of people in each age group by “shifting” each group 45–49 1,250
from 2000. For example, the number of 5- to 9-year-olds in
2005 will equal the number of 0- to 4-year-olds in 2000. 40–44 1,500

8. Calculate the total population for each five-year period. 35–39 2,000

9. Repeat the process described in steps 3–8 for each column, 30–34 2,500
to complete the table through the year 2050.
25–29 3,000
Analysis
20–24 4,000
1. Constructing Graphs Plot the growth of the population on
a line graph. You may want to use a computer to graph 15–19 5,000
the results.
10–14 6,500
2. Constructing Graphs Make a population pyramid for the
population in 2050. 5–9 8,000 10,000

Conclusions 0–4 10,000 12,500

3. Evaluating Data Compare your graphs with the graphs of Total 48,350
the other three groups. Were your predictions correct?
Females
4. Drawing Conclusions Which variable had a greater effect on
population growth—the number of children each woman that give
had or the age at which each woman had children?
birth 2,500
5. Interpreting Information Did any of the groups show no
growth in the population? Explain these results. New 12,500
births
Extension
̈ Sample Population Data Use
1. From the age-structure diagram on the previous page, what this table as an example to calculate
would you predict to happen to the U.S. population in the the age structure for each generation
next 20 years? in the next 50 years? What parts of the age of your imaginary population. Add
structure are most important to these predictions? columns for five-year periods up to
2050. Examples of some of Group A’s
results are shown in red.

Chapter 9 Skills Practice Lab 255

EARTH SCIENCE CONNECTION

FERTILITY RATES AND FEMALE LITERACY IN AFRICA

MAP SKILLS 2. Analyzing Data Choose 20 countries and make a
graph comparing the total fertility rates and female
Use the map of Africa to answer the questions literacy of each country.
below.
3. Comparing Data Worldwide, the average total fer-
1. Describing Locations Which regions of Africa tility rate is about 2.8 children per woman, and the
have the highest female literacy (percentage of average female literacy is 74 percent. How does Africa
females who can read and write)? the lowest female compare with the rest of the world in both aspects?
literacy? Which regions have the highest fertility
rates? the lowest fertility rates?

256 Chapter 9 Maps in Action

LOST POPULATIONS: WHAT HAPPENED?

At various points in human history, barren grassland. The island had ̈ These large stone figures found
entire populations have disappeared no tree or shrub that was more on Easter Island were made by a civ-
and left mysterious remains such as than 3 m tall. ilization that has disappeared.
the Egyptian pyramids and the
Anasazi pueblos in the southwestern A Changed Environment bird also became extinct, and the
United States. Why did these people human population crashed.
and their civilizations disappear? Researchers have now shown that
Archeologists sometimes find evi- Easter Island was very different The people of Easter Island
dence that environmental destruc- when it was first colonized by destroyed their environment by
tion was one of the reasons the Polynesians around 400 CE. In the overusing its natural resources and
populations disappeared. oldest garbage heaps on the island, introducing new species such as
archaeologists have found that one- chickens and rats. The people
Easter Island third of the bones came from dol- were reduced from a complex civi-
phins. To hunt dolphins, the lization to a primitive lifestyle.
On Easter Island in the Pacific islanders must have had strong Easter Island is a small-scale
Ocean, the first European visitors canoes made of wood from tall example of what ecologists worry
were amazed to find huge stone trees. Pollen grains, which are used could happen to Earth’s entire
heads that were miles from the to identify plants, show that the human population.
quarries where the heads had been island was once covered by a forest
made. It seemed impossible that that contained many species found
the islanders could have moved nowhere else in the world.
the heads. There were no horses,
oxen, or carts on the island and But by 1600 CE, trees were rare
there were also no trees, which and the Easter Island palm tree was
could have been used as rollers to extinct. The palm seeds were prob-
move the heads. The islanders ably eaten by rats that the
were using grass and reeds to Polynesians had brought to the
make fires because the island was island. With the destruction of the
forest, every species of native land

̈ These ruins in New Mexico were built by the Chaco Anasazi civilization
around 900 CE. Environmental changes are thought to have affected this
population.

What Do You Think?

Industrialized countries have
started to invest in environ-
mental improvements, such as
replanting forests that have
been destroyed and protect-
ing endangered species. Do
you think this makes these
countries safe from the kind of
environmental disasters that
destroyed the Easter Island
civilization?

Chapter 9 257

Biodiversity 10C H A P T E R

258 Chapter 10 Biodiversity 1 What Is Biodiversity?

2 Biodiversity at Risk

3 The Future of Biodiversity

PRE-READING ACTIVITY

Tri-Fold
Before you
read this chap-
ter, create the
FoldNote entitled “Tri-Fold”
described in the Reading and
Study Skills section of the
Appendix. Write what you
know about biodiversity in
the column labeled “Know.”
Then, write what you want
to know in the column
labeled “Want.” As you read
the chapter, write what you
learn about
biodiversity
in the col-
umn labeled
“Learn.”

How many species are in this photo?
Scientists know that this region of
Central Texas is home to an unusual
number of unique species. However,
many more species remain unknown
to science, both in faraway jungles
and in our own backyards.

SECTION 1

What Is Biodiversity?

Every day, somewhere on Earth, several unique species of organ- Objectives
isms become extinct as the last members of the species die—often
because of human actions. Scientists are not sure how many ̈ Describe the diversity of species
species are becoming extinct or even how many species there are types on Earth, relating the differ-
on Earth. How much extinction is natural? Can we—or should ence between known numbers
we—prevent extinctions? The study of biodiversity helps us think and estimated numbers.
about these questions, but does not give us all the answers.
̈ List and describe three levels of
A World Rich in Biodiversity biodiversity.

The term biodiversity, short for “biological diversity,” usually ̈ Explain four ways in which biodi-
refers to the number of different species in a given area. Certain versity is important to ecosystems
areas of the planet, such as tropical rain forests, contain an and humans.
extraordinary variety of species. The complex relationships
between so many species are hard to study, but humans may need ̈ Analyze the potential value of a
to understand and preserve biodiversity for our own survival. single species.

Unknown Diversity The study of biodiversity starts with the Key Terms
unfinished task of cataloging all the species that exist on Earth.
As shown in Figure 1, the number of species known to science is biodiversity
about 1.7 million, most of which are insects. However, the actual gene
number of species on Earth is unknown. Most scientists agree keystone species
that we have not studied Earth’s species adequately, but they ecotourism
accept an estimate of greater than 10 million for the total number
of species. New species are considered known when they are col- Figure 1 ̈ Number of Species on
lected and described scientifically. Unknown species exist in Earth About 1.7 million species on
remote wildernesses, deep in the oceans, and even in cities. Earth are known to science. Many
more species are estimated to exist,
■✓● Reading Check What determines whether a species is known or especially species of smaller organ-
isms. Scientists continue to revise
unknown? (See the Appendix for answers to Reading Checks.) these estimates.

Insects 1,600 Total known
Fungi Additional estimated

Arachnids 1,800 2,000 8,000
Nematodes

Bacteria
Plants

All others
Mollusks

Algae
Protozoans
Crustaceans
Vertebrates

0 200 400 600 800 1,000 1,200 1,400
Number of species (in thousands)

Source: World Conservation Monitoring Center.

Section 1 What Is Biodiversity? 259

Figure 2 ̈ Scientists continue to Levels of Diversity Biodiversity can be studied and described at
find and describe new species. three levels. Species diversity refers to the number of different
Specimens may be stored in collec- species in an area. This kind of diversity has received the most
tions such as this one of tropical attention and is most often what is meant by biodiversity.
birds, with tags that say where and Ecosystem diversity refers to the variety of habitats, communities,
when they were found. and ecological processes within and between ecosystems. Genetic
diversity refers to all the different genes contained within all
Figure 3 ̈ The sea otters of North members of a population. A gene is a piece of DNA that codes for
America are an example of a key- a specific trait that can be inherited by an organism’s offspring.
stone species, upon which a whole
ecosystem depends. Benefits of Biodiversity

Biodiversity can affect the stability of ecosystems and the sustain-
ability of populations. In addition, there are many ways that
humans clearly use and benefit from the variety of life-forms on
Earth. Biodiversity may be more important than we realize.

Species Are Connected to Ecosystems We depend on healthy
ecosystems to ensure a healthy biosphere that has balanced cycles
of energy and nutrients. Species are part of these cycles. When
scientists study any species closely, they find that it plays an
important role in an ecosystem. Every species is probably either
dependent on or depended upon by at least one other species in
ways that are not always obvious. When one species disappears
from an ecosystem, a strand in a food web is removed. How
many threads can be pulled from the web before it collapses? We
often do not know the answer until it is too late.

Some species are so clearly critical to the functioning of an
ecosystem that they are called keystone species. One example of a
keystone species is the sea otter. Figure 3 shows how the loss of
sea otter populations led to the loss of the kelp beds along the
U.S. Pacific coast and how the recovery of otter populations led
to the recovery of the kelp populations.

In the 1800s, Sea urchins, with In 1937, a small group of surviving The otters once again preyed
sea otters were no more predators, otters was discovered. With pro- on the sea urchins. The kelp
hunted for their multiplied and ate all tection and scientific efforts, the beds regenerated.
fur. They dis- of the kelp. The kelp otter populations grew.
appeared from beds began to dis-
the Pacific coast appear from the area.
of the U.S.

260 Chapter 10 Biodiversity

Species and Population Survival Genetic diversity within popu- Population size Bottleneck
lations is critical to species survival. Genetic diversity increases the
chance that some members of a population will survive environ- Time
mental changes. Small and isolated populations are less likely to Genetic types
survive such changes. When a population shrinks, its genetic
diversity decreases as though it is passing through a bottleneck, Figure 4 ̈ When a population is
represented in Figure 4. Even if the population can increase again, reduced to a few members, this cre-
its genetic diversity will be reduced. Then, members of the popula- ates a bottleneck of reduced genetic
tion may become more likely to inherit genetic diseases. diversity. The genetic diversity of the
population is greater before the bot-
Medical, Industrial, and Agricultural Uses People throughout tleneck than after it.
history have used the variety of organisms on Earth for food,
clothing, shelter, and medicine. About one quarter of the drugs www.scilinks.org
prescribed in the United States are derived from plants. Almost all
antibiotics are derived from chemicals found in fungi. Table 1 lists Topic: Biodiversity
some plants from which medicines are derived. Code: HE80151
Topic: Medicines from
For some industries, undiscovered and poorly studied species
represent a source of potential products. New chemicals and Plants
industrial materials may be developed from chemicals discovered Code: HE80934
in all kinds of species. The scientific community continues to find
new uses for biological material and genetic diversity.

■✓● Reading Check Why is genetic diversity important for the survival

of a species?

Table 1 ̄

Common Medicines Derived from Plants

Medicine Origin Use

Neostigmine calabar bean treatment of glaucoma and
(Africa) basis for synthetic insecticides

Turbocurarine curare vine surgical muscle relaxant;
(South America) treatment of muscle disorders;
and poison for arrow tips

Vincristine, rosy periwinkle treatment of pediatric leukemia
vinblastine (Madagascar) and Hodgkin’s disease

Bromelain pineapple treatment to control tissue

(South America) inflammation

Taxol Pacific yew anticancer agent

(North America)

Novacaine, coca plant local anesthetic and basis for
cocaine
(South America) many other anesthetics

Cortisone wild yam hormone used in many drugs

(Central America)

L-dopa velvet bean treatment of Parkinson’s disease
(levodopa) (tropical Asia)

Reserpine Indian snakeroot treatment to reduce high blood

(Malaysia) pressure

Section 1 What Is Biodiversity? 261

Figure 5 ̈ A produce market in
Bolivia shows a diversity of native
foods. Food crops that originated in
the American tropics include corn,
tomatoes, squash, and many types
of beans and peppers.

Table 2 ̄ Humans benefit from biodiversity every time they eat. Most of
the crops produced around the world originated from a few areas
Origins of Some Foods of high biodiversity. Some examples of crop origins are shown in
Figure 5 and Table 2. Most new crop varieties are hybrids, crops
North America, Central developed by combining genetic material from more than one
America, and South America population. Depending on too few plant varieties for food is risky.
For example, famines have resulted when an important crop was
• corn (maize), tomato, bean wiped out by disease. But some crops have been saved from dis-
(pinto, green, and lima), eases by being crossbred with wild plant relatives. In the future,
peanut, potato, sweet potato, new crop varieties may come from species not yet discovered.
avocado, pumpkin, pineapple,
cocoa, vanilla, and pepper Ethics, Aesthetics, and Recreation Some people believe that we
(green, red, and chile) should preserve biodiversity for ethical reasons. They believe that
species and ecosystems have a right to exist whether or not they
Northeastern Africa, Central have any other value. To people of some cultures and religions,
Asia, and Near East each organism on Earth is a gift with a higher purpose.

• wheat (several types), sesame, People also value biodiversity for aesthetic or personal enjoy-
chickpea, fig, lentil, carrot, pea, ment—keeping pets, camping, picking wildflowers, or watching
okra, date, walnut, coffee, cow, wildlife. Some regions earn the majority of their income from
goat, pig, and sheep ecotourism, a form of tourism that supports the conservation and
sustainable development of ecologically unique areas.
India, East Asia, and
Pacific Islands

• soybean, rice, banana, coconut,
lemon, lime, orange, cucum-
ber, eggplant, turnip, tea, black
pepper, and chicken

S E C T I O N 1 Review

1. Describe the general diversity of species on Earth in CRITICAL THINKING
terms of relative numbers and types of organisms.
Compare known numbers to estimates. 4. Analyzing a Viewpoint Is it possible to put a
price on a single species? Explain your answer.
2. Describe three levels of biodiversity. Which level is
most commonly meant by biodiversity? 5. Predicting Consequences What is your favorite
type of organism? If this organism were to go extinct,
3. Explain how biodiversity is important to ecosystems, how would you feel? What would you be willing to
and give examples of how it is important to humans. do to try to save it from extinction? Write a short
essay describing your reaction. WRITING SKILLS

262 Chapter 10 Biodiversity

SECTION 2

Biodiversity at Risk

About 65 million years ago, a series of changes in the Earth’s Objectives
climate and ecosystems caused the extinction of about half the
species on Earth. The extinction of many species in a relatively ̈ Define and give examples of
short period of time is called a mass extinction. Earth has experi- endangered and threatened species.
enced several mass extinctions, as shown in Figure 6. It takes mil-
lions of years for biodiversity to rebound after a mass extinction. ̈ Describe several ways that species
are being threatened with extinc-
Current Extinctions tion globally.

Scientists are warning that we are in the midst of another mass ̈ Explain which types of threats are
extinction. The rate of extinction is estimated to have increased having the largest impact on bio-
by a multiple of 50 since 1800. Between 1800 and 2100, up to diversity.
25 percent of all species on Earth may have become extinct. The
current mass extinction is different from those of the past because ̈ List areas of the world that have
humans are the primary cause of the extinctions. high levels of biodiversity and
many threats to species.

̈ Compare the amount of biodiver-
sity in the United States to that of
the rest of the world.

Species Prone to Extinction Cockroaches and rats are not likely to Key Terms
become extinct because they have large populations that adapt easi-
ly to many habitats. But species with small populations in limited endangered species
areas can easily become extinct. Species that are especially at risk of threatened species
extinction include those that migrate, those that need large or spe- exotic species
cial habitats, and those that are exploited by humans. poaching
endemic species
An endangered species is a species that is likely to become
extinct if protective measures are not taken immediately. A Figure 6 ̈ Biodiversity has generally
threatened species is a species that has a declining population and increased over time, as indicated
that is likely to become endangered if it is not protected. Additional here by the numbers of marine
categories of risk exist for certain legal and biological purposes. families. The past five mass extinctions
were probably caused by global
■✓● Reading Check Why do scientists warn that a mass extinction is climate changes.

occurring now?

Major Extinction Events Over Geological Time

1,200

Number of marine families 1,000

800
Major extinction events

600

400

200

0 400 300 200 100 0
500 Millions of years ago

Section 2 Biodiversity at Risk 263

Table 3 ̄ Species Known to Be Threatened or Extinct Worldwide
Type of species
Number threatened Number extinct Percent of species
(all categories of risk) (since ~1800) that may be threatened

Mammals 1,130 87 26
Birds 1,183 131 12
Reptiles
Amphibians 296 22 3.3
Fishes 146 5 3.1
Insects 751 3.7
Other crustaceans 555 92 0.054
Mollusks and worms 555 73 1.03
Plants 944 73 1.3
30,827 303 0.054
400

Source: UN Environment Programme. How Do Humans Cause Extinctions?

Figure 7 ̈ The purple area on the In the past 2 centuries, human population growth has accelerated
map below shows the range of the and so has the rate of extinctions. The numbers of worldwide
Florida panther when settlers first species known to be threatened, endangered, or recently extinct
arrived in the southeastern United are listed in Table 3. The major human causes of extinction today
States. Fewer than 100 of this cougar are the destruction of habitats, the introduction of nonnative
subspecies (right) remain in the wild. species, pollution, and the overharvesting of species.

Habitat Destruction and Fragmentation As human populations
grow, we use more land to build homes and harvest resources. In
the process, we destroy and fragment the habitats of other species.
It is estimated that habitat loss causes almost 75 percent of the
extinctions now occurring.

Due to habitat loss, the Florida panther is one of the most
endangered animals in North America. The panther and its histori-
cal range are shown in Figure 7. Two hundred years ago, cougars—

264 Chapter 10 Biodiversity

a species that includes panthers and mountain lions—ranged from Connection to Ecology
Alaska to South America. Cougars require expansive ranges of for-
est habitat and large amounts of prey. Today, much of the cougars’ Extinction and Global Change
habitat has been destroyed or broken up by roads, canals, and Scientists have worried for some
fences. In 2003, fewer than 100 Florida panthers made up the only time that environmental pollu-
remaining wild cougar population east of the Mississippi River. tants might cause drastic changes
in our atmosphere and biosphere.
Invasive Exotic Species An exotic species is a species that is not However, it is difficult to draw a
native to a particular region. Even such familiar organisms as cats direct link from global changes to
and rats are considered to be exotic species when they are specific extinctions.
brought to regions where they never lived before. Exotic species
can threaten native species that have no natural defenses against In recent decades, scientists
them. The invasive fire ants in Figure 8 threaten livestock, people, have observed a worldwide
and native species throughout the southeastern United States. decline in amphibian species.
Unlike most cases of habitat loss
Harvesting, Hunting, and Poaching Excessive hunting and har- or overhunting, there are no clear
vesting of species can also lead to extinction. In the United States causes for these extinctions. But
in the 1800s and 1900s, 2 billion passenger pigeons were hunted there is growing evidence to indi-
to extinction and the bison was hunted nearly to extinction. cate two probable causes: the
Thousands of rare species worldwide are harvested and sold for pollution of water sources with
use as pets, houseplants, wood, food, or herbal medicine. hormone-like chemicals and
increased UV radiation exposure
Many countries now have laws to regulate hunting, fishing, due to the thinning of the Earth’s
harvesting, and trade of wildlife. However, these activities continue ozone layer.
illegally, a crime known as poaching. In poor countries especially,
local species are an obvious source of food, medicine, or income. Figure 8 ̈ Mounds made by
Moreover, not all threatened species are legally protected. imported fire ants cover many fields
in the southeastern United States. As
Pollution Pesticides, cleaning agents, drugs, and other chemicals with many invasive exotic species,
used by humans are making their way into food webs around the these ants had no natural predators
globe. The long-term effects of chemicals may not be clear until and little competition from native
after many years of use. The bald eagle is a well-known example species when they were first brought
of a species that was endangered because of a pesticide known as into the country by accident.
DDT. Although DDT is now illegal to use in the United States, it
is still manufactured here and used around the world.

Section 2 Biodiversity at Risk 265

MATHPRACTICE Areas of Critical Biodiversity

Estimating Species Loss Some parts of the world contain a greater diversity of species
The annual loss of tropical than others. An important feature of such areas is that they have
forest habitat is estimated at a large portion of endemic species, meaning species that are
about 1.8 percent per year. Some native to and found only within a limited area. Ecologists often
scientists estimate that this habitat use the numbers of endemic species of plants as an indicator of
loss results in a loss of about 0.5 overall biodiversity, because plants form the basis of ecosystems
percent of species per year. Given on land. Ecologists increasingly point out the importance of bio-
a low estimate of only 5 million diversity in oceans, though marine ecosystems are also complex
species on Earth, how many years and poorly understood.
would it take for 1 million species
to be lost, if current rates of tropi- Tropical Rain Forests The remaining tropical rain forests cover less
cal forest habitat loss continue? than 7 percent of the Earth’s land surface. Yet biologists estimate that
over half of the world’s species live in these forests. Most of these
species have never been described. Unknown numbers of species are
disappearing as tropical forests are cleared for farming or cattle
grazing. Meanwhile, tropical forests are among the few places where
some native people maintain traditional lifestyles and an intimate
knowledge of their forest homes. The case study below explains the
increasing value of such knowledge in the global marketplace.

A Genetic Gold Rush
in the Rain Forests

How much is a species worth? To some reasons to venture into the ̈ This botanist is researching the
some people, there is money to be wilderness may be economic. The uses of rain-forest plants and other
made in centers of biodiversity such biotechnology industry is based on species with the help of local people.
as rain forests. Thus, the Amazon the application of biological science
rain forest in South America is wit- to create new products such as
nessing an increase in visitors—not drugs. This industry depends on
just tourists, but scientists seeking Earth’s variety of organisms—
genes, glory, or enlightenment into especially their genetic material—
the mysteries of these quickly disap- for research and development.
pearing treasures.
In fact, the Brazilian government
To biologists, the prospect of has taken notice of the increased
discovering new species may be a international interest in the Amazon’s
chance at fame. The first scientist amazing biological assets. The gov-
to collect and describe a species ernment has claimed the right to tax
often gets to choose a name for or patent any genetic material har-
that species. For other scientists, vested from within its borders.
researching the unknown inner
workings of the rain forests is an Other researchers are more inter-
adventure similar to the adventures ested in another special feature of
of explorers charting new lands. the Amazon—native peoples. Some
Amazonian natives, such as the
But like the quests of early Yanomamö, are still living a lifestyle
European explorers of the Americas, of intimate connection to their forest

266 Chapter 10 Biodiversity

Coral Reefs and Coastal Ecosystems Coral reefs occupy a small Geofact
fraction of the marine environment yet contain the majority of the
biodiversity there. Reefs provide millions of people with food and The World’s Largest Reef The
tourism revenue. They protect coasts from waves and are sources Great Barrier Reef of Australia is the
of new chemicals. But reefs are poorly studied and are not well largest and probably the oldest reef
protected by laws. Nearly 60 percent of Earth’s coral reefs are system in the world. It stretches for
threatened by human activities, such as overfishing and pollution. 2,000 km (1,250 mi) and consists
Similar threats affect coastal ecosystems, such as swamps, marshes, of 3,400 individual reefs.
shores, and kelp beds. Coastal areas are travel routes for many
migrating species as well as links to ecosystems on land.

Islands When an island rises from the sea, it is colonized by a lim-
ited number of species from the mainland. These colonizing species
may then evolve into several new species. Thus, islands often hold
a very distinct but limited set of species. For example, the
Hawaiian Islands have 28 species of an endemic family of birds
called honeycreepers. Honeycreepers and many other island species
are endangered by competition from exotic species.

■✓● Reading Check Why is the biodiversity of coral reefs and coastal

ecosystems threatened?

̈ The Yanomamö are among the
few native peoples of the tropical
rain forests who still live traditional
lifestyles and use their knowledge of
the forests to meet all of their needs.

for their use of the skin excretions
of poison dart frogs for hunting.

Often, researchers originally
learned of a useful species from a
local shaman, or healer. Biochemistry
researchers have been amazed by
the complex combinations of new
chemicals they have discovered in
many rain-forest species. Some of
these chemicals are already being
used in research and medicine.

home, in much the same way as being able to recognize or name CRITICAL THINKING
they have for thousands of years. species. For example, the
Yanomamö make use of thousands 1. Expressing Viewpoints To
An important value of such of plants, fungi, and animals for whom do you think the genetic
native peoples is their vast knowl- food, drugs, weapons, and art. material of the rain forests should
edge of the variety of species in the Amazonian natives such as the belong? What are some ways this
ecosystems where they live. Their Yanomamö are probably best known benefit of biodiversity might be
knowledge includes more than just shared with the whole world?

Section 2 Biodiversity at Risk 267

www.scilinks.org Biodiversity Hotspots The most threatened areas of high species
diversity on Earth have been labeled biodiversity hotspots.
Topic: Endangered Twenty-five of these areas, shown in Figure 9, have been identified
Species by international conservationists. The hotspot label was developed
by ecologists in the late 1980s to identify areas that have high
Code: HE80502 numbers of endemic species but that are also threatened by human
activities. Most of these hotspots have lost at least 70 percent of
Figure 9 ̈ Conservationists have their original natural vegetation. The hotspots include mostly
identified these 25 biodiversity tropical rainforests, coastal areas, and islands. In Madagascar, for
hotspots (green). Examples of example, only 18 percent of the original forests remain. More
endangered species from some than 80 percent of Madagascar’s 10,000 flowering plant species
areas are shown. are endemic, as are 91 percent of its 300 reptile species. All 33
species of lemur, which make up a tenth of the world’s primate
species, are found only in Madagascar.

Mediterranean Basin Mountains of Philippines
Gray’s monitor lizard
Dragon tree South-Central China

Caucasus

Polynesia and Micronesia Western Ghats Indo-Burma
Akiapolaau and Sri Lanka

California
floristic
province

Caribbean

Mesoamerica Brazilian
Cerrado

Tropical Guinea Sundaland New
Andes forests of Caledonia
West Africa Wallacea
Chocó-Darién and New Zealand
Western Ecuador Succulent Madagascar and Southwest
Marinkelle’s sword-nosed bat Indian Ocean islands Australia
Karoo Lesser mouse lemur
Central
Chile Atlantic

forest Cape
region floristic

province

Eastern Arc
Mountains
and coastal

forests
of Tanzania
and Kenya

268 Chapter 10 Biodiversity

Biodiversity in the United States You may notice that three of Figure 10 ̈ Examples of at-risk
the biodiversity hotspots in Figure 9 are partly within U.S. bor- species and populations in the
ders. The United States includes a wide variety of unique United States include the cecropia
ecosystems, including the Florida Everglades, the California moth, (declining populations),
coastal region, Hawaii, the Midwestern prairies, and the forests
of the Pacific Northwest. The United States holds unusually the tulip poplar tree (limited
high numbers of species of freshwater fishes, mussels, snails, distribution), the crayfish
and crayfish. Species diversity in the United States is also high Cambarus mongalensis (limited
among groups of land plants such as pine trees and sunflowers. distribution), the desert pupfish
Some examples of the many species and populations that are at (endangered), and the northern
risk of being lost are shown in Figure 10. spotted owl (threatened).

The California Floristic Province, a biodiversity hotspot, is
home to 3,488 native plant species. Of these species, 2,124 are
endemic and 565 are threatened or endangered. The threats to
this area include the use of land for agriculture and housing, dam
construction, overuse of water, destructive recreation, and
mining—all stemming from local human population growth.

S E C T I O N 2 Review

1. Describe four ways that species are being threatened CRITICAL THINKING
with extinction globally.
5. Interpreting Graphics The biodiversity hot spots
2. Define and give examples of endangered species and shown in Figure 9 share several characteristics besides
threatened species. a great number of species. Look at the map, and
name as many shared characteristics as you can.
3. List areas of the Earth that have high levels of biodi-
versity and many threats to species. 6. Expressing Opinions Which of the various threats
to biodiversity do you think will be most difficult to
4. Compare the amount of biodiversity in the United stop? Which are hardest to justify? Write a paragraph
States to that of the rest of the world. to explain your opinion. WRITING SKILLS

Section 2 Biodiversity at Risk 269

SECTION 3

The Future of Biodiversity

Objectives Slowing the loss of species is possible, but to do so we must
develop new approaches to conservation and sensitivity to human
̈ List and describe four types of needs around the globe. In this section, you will read about
efforts to save individual species. efforts to save individual species and to protect entire ecosystems.

̈ Explain the advantages of protect- Saving Species One at a Time
ing entire ecosystems rather than
individual species. When a species is clearly on the verge of extinction, concerned
people sometimes make extraordinary efforts to save the last few
̈ Describe the main provisions of individuals. These people hope that a stable population may be
the Endangered Species Act. restored someday.

̈ Discuss ways in which efforts to Captive-Breeding Programs Sometimes, wildlife experts may
protect endangered species can attempt to restore the population of a species through captive-
lead to controversy. breeding programs. These programs involve breeding species in
captivity, with the hope of reintroducing populations to their
̈ Describe three examples of world- natural habitats. One example of a captive-breeding program
wide cooperative efforts to prevent involves the California condor, shown in Figure 11.
extinctions.
Condors are scavengers. They typically soar over vast areas
Key Terms in search of dead animals to eat. Habitat loss, poaching, and

germ plasm lead poisoning brought the species near extinction. In 1986,
Endangered Species Act the nine remaining wild California condors were captured
habitat conservation plan by wildlife experts to protect the birds and to begin a breed-
Biodiversity Treaty ing program. Birds bred in captivity were released into the
wild in the hope that they would breed there. By 2005, there
were 121 condors in the wild, a few of them juveniles that

had hatched from eggs laid in the wild. The survival of
this species remains doubtful.

Preserving Genetic Material One way to save the
essence of a species is by preserving its genetic material.

Germ plasm is any form of genetic material, such as
that contained within the reproductive, or germ, cells

Figure 11 ̈ The California
condor (above) nearly became
extinct in the 1980s. A captive-
breeding program (right) is
returning some condors to
the wild.

270 Chapter 10 Biodiversity

of plants and animals. Germ-plasm banks store germ plasm for Figure 12 ̈ This scientist is handling
future use in research or species-recovery efforts. Material may be samples of genetic material that are
stored as seeds, sperm, eggs, or pure DNA. Germ plasm is usually preserved in controlled conditions.
stored in special controlled environments, such as that shown in The samples may be able to repro-
Figure 12, to keep the genetic material intact for many years. duce organisms many years from now.
Farmers and gardeners also preserve germ plasm when they save
and share seeds.

Zoos, Aquariums, Parks, and Gardens The original idea of zoos
was to put exotic animals on display. However, in some cases,
zoos now house the few remaining members of a species and are
perhaps the species’ last hope for survival. Zoos, wildlife parks,
aquariums, and botanical gardens are living museums of the
world’s biodiversity. Botanical gardens, such as the one shown in
Figure 13, house about 90,000 species of plants worldwide. Even
so, these kinds of facilities rarely have enough resources or
knowledge to preserve more than a fraction of the world’s rare
and threatened species.

More Study Needed Ultimately, saving a few individuals does
little to preserve a species. Captive species may not reproduce or
survive again in the wild. Also, small populations are vulnerable
to infectious diseases and genetic disorders caused by inbreeding.
Conservationists hope that these strategies are a last resort to
save species.

Spider Map

Create the
Graphic Organizer entitled
“Spider Map” described in the
Appendix. Label the circle
“Conservation Efforts.” Create a
leg for each kind of conservation
effort. Then, fill in the map with
details about each of
the ways people today
are trying to preserve
diversity.

Figure 13 ̈ This botanical garden is
contained within a clear dome in
Queen Elizabeth Park in Vancouver,
Canada. The dome houses over 500
species of plants from all over the
world as well as over 100 species of
tropical birds.

Section 3 271

Figure 14 ̈ Another conservation
strategy is to promote more creative
and sustainable land uses. This coffee
crop is grown in the shade of native
tropical trees instead of on cleared
land. This practice is restoring habitat
for many migrating songbirds.

www.scilinks.org Preserving Habitats and Ecosystems

Topic: Preserving The most effective way to save species is to protect their habitats.
Ecosystems But a species confined to a small area could be wiped out by a sin-
gle natural disaster. Some species require a large range to find ade-
Code: HE81214 quate food, find a suitable mate, and rear their young. Therefore,
protecting the habitats of endangered and threatened species often
QuickLAB means preserving or managing large areas.

Design a Wildlife Preserve Conservation Strategies Most conservationists now give priority
to protecting entire ecosystems rather than individual species. By
Procedure protecting entire ecosystems, we may be able to save most of the
1. Imagine you have enough species in an ecosystem instead of only the ones that have been
identified as endangered. The public has begun to understand
money and political support to that Earth’s biosphere depends on all its connected ecosystems.
set aside some land in your
community to be habitat for To protect biodiversity worldwide, conservationists focus on
local wildlife. Your goal is to the hotspots described in the previous section. However, they also
decide which areas to preserve. support additional strategies. One strategy is to identify areas of
2. Find out which species in your native habitat that can be preserved, restored, and linked into
area would need this protection large networks. Another promising strategy is to promote prod-
the most, where they currently ucts that have been harvested with sustainable practices, such as
exist, and what their habitat the shade-grown coffee shown in Figure 14.
needs are.
3. Use a colored pencil to draw More Study Needed Conservationists emphasize the need for
some proposed preserve areas more serious study of ecosystems. Only in recent decades has there
on a copy of a local map. been research into such basic questions as, How large does a pro-
Analysis tected preserve have to be to maintain a certain number of species?
1. Explain why you chose the How much fragmentation can a particular ecosystem tolerate? The
areas you did. Can you connect answers may be years or decades away, but decisions affecting bio-
or improve any existing areas of diversity continue to be made based on available information.
habitat? How could you reduce
various threats to the species? ■✓● Reading Check Why does protecting the habitat of threatened and

272 Chapter 10 Biodiversity endangered species involve large areas?

Legal Protections for Species Table 4 ̄

Many nations have laws and regulations designed to prevent the Major Provisions of the
extinction of species, and those in the United States are among Endangered Species Act
the strongest. Even so, there is controversy about how to enforce
such laws and about how effective they are. • The U.S. Fish and Wildlife
Service (USFWS) must compile
U.S. Laws In 1973, the U.S. Congress passed the Endangered a list of all endangered and
Species Act and has amended it several times since. This law, threatened species.
summarized in Table 4, is designed to protect plant and animal
species in danger of extinction. Under the first provision, the U.S. • Endangered and threatened
Fish and Wildlife Service (USFWS) must compile a list of all animal species may not be
endangered and threatened species in the United States. As of caught or killed. Endangered
2005, 1,272 species of plants and animals were listed as endan- and threatened plants on
gered or threatened. Dozens more are considered for the list each federal land may not be
year. The second main provision of the act protects listed species uprooted. No part of an
from human harm. Anyone who harms, buys, or sells any part of endangered and threatened
these species is subject to a fine. The third provision prevents the species may be sold or traded.
federal government from carrying out any project that jeopardizes
a listed species. • The federal government may
not carry out any project that
Recovery and Habitat Conservation Plans Under the fourth main jeopardizes endangered
provision of the Endangered Species Act, the USFWS must prepare species.
a species recovery plan for each listed species. These plans often
propose to protect or restore habitat for each species. However, • The U.S. Fish and Wildlife
attempts to restrict human uses of land can be controversial. Real- Service must prepare a species
estate developers may be prohibited from building on their own recovery plan for each
land because it contains critical habitat for a species. People may endangered and threatened
lose income when land uses are restricted and may object when species.
their interests are placed below those of another species.

Although battles between developers and environmental-
ists are widely publicized, in most cases compromises are
eventually worked out. One form of compromise is a habitat
conservation plan—a plan that attempts to protect one or more
species across large areas of land through trade-offs or cooper-
ative agreements. The region of California shown in Figure 15
is part of a habitat conservation plan.

Figure 15 ̈ This region of San
Diego, California, is home to several
endangered species. A habitat con-
servation plan attempts to protect
these species by managing a large
group of lands in the area.

Section 3 273

Figure 16 ̈ Scenes like this one International Cooperation
of elephant tusk poaching were
common before the worldwide ban At the global level, the International Union for the Conservation
on the sale of ivory as part of CITES. of Nature and Natural Resources (IUCN) facilitates efforts to
protect species and habitats. This organization is a collaboration
MATHPRACTICE of almost 200 government agencies and over 700 private conser-
vation organizations. The IUCN publishes Red Lists of species in
Measuring Risk There danger of extinction around the world. The IUCN also advises
are many ways to categorize governments on ways to manage their natural resources, and
a species’ degree of risk of works with groups like the World Wildlife Fund to sponsor con-
extinction. The IUCN and the servation projects.
Nature Conservancy have multiple
ranks for species of concern, rang- International Trade and Poaching One product of the IUCN has
ing from “presumed extinct” to been an international treaty called CITES (the Convention on
“secure.” According to one study International Trade in Endangered Species). The CITES treaty
of 20,500 species in the United was the first effective effort to stop the slaughter of African el-
States, 1,400 of those species were ephants. Elephants were being killed by poachers who would sell
at some risk. Calculate this number the ivory tusks. Efforts during the 1970s and 1980s to limit the
of species at risk as a percentage. sale of ivory did little to stop the poaching. Then in 1989, the
Use this percentage to estimate members of CITES proposed a worldwide ban on all trade in
how many species may be at risk ivory, hoping to prevent scenes like those in Figure 16.
around the world.
Some people worried that making ivory illegal might increase
274 Chapter 10 Biodiversity the rate of poaching instead of decrease it. They argued that ille-
gal ivory, like illegal drugs, might sell for a higher price. But after
the ban was enacted, the price of ivory dropped, and elephant
poaching declined dramatically.

The Biodiversity Treaty One of the most ambitious efforts to
tackle environmental issues on a worldwide scale was the United
Nations Conference on Environment and Development, also known
as the first Earth Summit. More than 100 world leaders and 30,000
other participants met in 1992 in Rio de Janeiro, Brazil.

■✓● Reading Check Describe one way in which the IUCN helps to pro-

tect species and habitats.

An important result of the Earth Summit Figure 17 ̈ These Greenpeace
was an international agreement called the activists are blocking the path of a
Biodiversity Treaty. The treaty’s goal is to Japanese whaling ship. Do you think
preserve biodiversity and ensure the sustain- this is an effective way to protect
able and fair use of genetic resources in all species?
countries. However, the treaty took many
years to be adopted into law by the U.S. gov- FIELD ACTIVITY
ernment. Some political groups objected to the
Treaty, especially to the suggestion that eco- Simple Biodiversity
nomic and trade agreements should take into Assessment Discover the diver-
account any impacts on biodiversity that sity of weeds and other plants in
might result from the agreements. The interna- a small area. Yards, gardens, and
tional community will thus continue to have vacant lots are good places to
debates like those that have surrounded the conduct such a study. Mark off a
Endangered Species Act in the United States. 0.5 m2 section. Use a field guide
to identify every plant species that
Private Conservation Efforts Many private organizations work you can. At least identify how
to protect species worldwide, often more effectively than govern- many different kinds of plants
ment agencies. The World Wildlife Fund encourages the sustain- there are. You may want to sketch
able use of resources and supports wildlife protection. The Nature or photograph some of the plants.
Conservancy has helped purchase millions of hectares of habitat Then count the number of each
preserves in 29 countries. Conservation International helps iden- kind of plant you identified. Record
tify biodiversity hotspots and develop ecosystem conservation your results in your EcoLog.
projects in partnership with other organizations and local people.
Greenpeace International organizes direct and sometimes con-
frontational actions, such as the one shown in Figure 17, to
counter environmental threats.

Balancing Human Needs

Attempts to protect species often come into conflict with the
interests of the world’s human inhabitants. Sometimes, an
endangered species represents a source of food or income. In
other cases, a given species may not seem valuable to those who
do not understand the species’ role in an ecosystem. Many con-
servationists feel that an important part of protecting species is
making the value of biodiversity understood by more people.

S E C T I O N 3 Review

1. Describe four types of efforts to save individual CRITICAL THINKING
species. 5. Analyzing Methods Read the headings in this sec-

2. Explain the advantages of protecting entire ecosys- tion. Which type of effort to preserve species do you
tems rather than individual species. think is most worthwhile? READING SKILLS

3. Describe the main provisions of the Endangered 6. Comparing Viewpoints Discuss ways in which
Species Act. efforts to protect species can lead to controversy.

4. Give examples of worldwide cooperative efforts to 7. Inferring Relationships Why was a complete ban
prevent extinctions. of ivory sales more effective than a limited ban?

Section 3 The Future of Biodivesity 275

10C H A P T E R Highlights

1 What Is Biodiversity? Key Terms Main Ideas

biodiversity, 259 ̈ Biodiversity usually refers to the number of
gene, 260 different species in a given area.
keystone species, 260
ecotourism, 262 ̈ The study of biodiversity starts with the
unfinished task of identifying and cataloging all
species on Earth. Although scientists disagree
about the probable number of species on Earth,
they do agree that we need to study biodiver-
sity more thoroughly.

̈ Humanity benefits from biodiversity in several
ways and perhaps in some unknown ways.

2 Biodiversity at Risk endangered species, ̈ Many scientists are now concerned that loss
263 of biodiversity is the most challenging environ-
mental issue we face.
threatened species,
263 ̈ The most common cause of extinction today
is the destruction of habitats by humans.
exotic species, 265 Unregulated hunting and the introduction of
nonnative species also contribute to extinctions.
poaching, 265
̈ Certain areas of the world contain a greater
endemic species, 266 diversity of species than other areas. An impor-
tant feature of such areas is that they have a
large portion of endemic species.

̈ The United States has a very important role
in preserving biodiversity.

3 The Future of Biodiversity germ plasm, 270 ̈ Most major conservation efforts now con-
centrate on protecting entire ecosystems rather
276 Chapter 10 Highlights Endangered Species than individual species.
Act, 273
̈ The Endangered Species Act establishes pro-
habitat conservation tections for endangered and threatened species
plan, 273 in the United States. The act has generated
some controversy and has been amended
Biodiversity Treaty, several times.
275
̈ International cooperation has led to
increased recognition and protection of biodi-
versity worldwide.

̈ The desire to protect biodiversity often con-
flicts with other human interests.

10C H A P T E R Review

Using Key Terms 11. A mass extinction is
a. a rapid increase in biodiversity.
Use each of the following terms in a separate b. the introduction of exotic species.
sentence. c. the extinction of many species in a short
period of time.
1. keystone species d. a benefit to the environment.

2. ecotourism 12. When sea otters disappeared from the Pacific
coast of North America,
For each pair of terms, explain how the meanings a. the area became overrun with kelp.
of the terms differ. b. the number of fish in the kelp beds
increased.
3. hunting and poaching c. the number of sea urchins in the kelp beds
increased.
4. endemic species and exotic species d. the area became overrun with brown
seaweed.
5. endangered species and threatened species
13. Which of the following statements about the
6. gene and germ plasm Endangered Species Act is not true?
a. Parts of an endangered animal, such as
7. CITES and Biodiversity Treaty feathers or fur, may be traded or sold but
only if the animal is not killed.
STUDY TIP b. A species is considered endangered if it is
expected to become extinct in the near
Use a Map As you review the chapter, refer to an future.
atlas, to the maps in the Appendix, or to previous c. The federal government cannot carry out
chapters about biomes to compare information. a project that may jeopardize an endan-
Draw your own map or make a list of the locations gered plant.
of some of the interesting species and ecosystems d. A recovery plan is prepared for all animals
that you learn about. that are listed as endangered.

Understanding Key Ideas 14. Because of efforts by the Convention on
International Trade in Endangered Species
8. The term biodiversity refers to (CITES),
a. the variety of species on Earth. a. the poaching of elephants increased.
b. the extinction of the dinosaurs. b. the cost of ivory worldwide increased.
c. habitat destruction, invasive exotic species, c. the international trade of ivory was banned
and poaching. worldwide.
d. the fact that 40 percent of prescription d. a captive-breeding program for elephants
drugs come from living things. was established.

9. Most of the living species known to science 15. Emphasizing the preservation of entire
a. are large mammals. ecosystems will
b. live in deserts. a. cause the economic needs of farmers to
c. live in the richer countries of the world. suffer in order to save a single species.
d. are insects. b. decrease biodiversity, especially in tropical
rain forests, coral reefs, and islands.
10. Some species are so important to the func- c. throw the food webs of many ecosystems
tioning of an ecosystem that they are called out of balance.
a. threatened species. d. save many unknown species from
b. keystone species. extinction.
c. endangered species.
d. extinct species.

Chapter 10 Review 277

10C H A P T E R Review

Short Answer Concept Mapping ?
??
16. When was hunting a major cause of extinc-
tions in the United States? 24. Use the following terms to create a concept
map: biodiversity, species, gene, ecosystem,
17. What are exotic species, and how do they habitat loss, poaching, exotic species, germ
endanger other species? plasm, captive breeding programs, and habi-
tat preservation.
18. Why do biologists favor using an ecosystem
approach to preserve biodiversity? Critical Thinking

19. Describe three ways that preserving biodi- 25. Comparing Processes Read the passage in
versity can come into conflict with human this chapter that describes current extinc-
interests. tions. How are the extinctions that are
occurring currently different from most
Interpreting Graphics extinctions in the past? READING SKILLS

The graph below shows the numbers of various 26. Analyzing Methods With unlimited funding,
types of species that are officially listed as endan- could zoos and captive-breeding programs
gered or threatened in the United States and restore most endangered animal popula-
internationally. Use the graph to answer ques- tions? Explain your answers.
tions 20–23.
27. Determining Cause and Effect How might
20. Do these numbers necessarily reflect all the loss of huge tracts of tropical rain forests
species that may be in danger? Explain your have an effect on other parts of the world?
answer.
Cross-Disciplinary Connection
21. Which types of species might be underrepre-
sented here? 28. Literature Try to remember or find some
children’s stories that include wild animals
22. Compare the United States and world list- that are currently endangered, threatened,
ings. What trends do you see in the types of or extinct. Write a description of how these
species listed? animals are portrayed in the stories. Also
compare the animals in the stories to what
23. Given this information, which types of you know about the real animals.
species might need further research
worldwide? WRITING SKILLS

Mammals 29. Geography Obtain a list of the plants and
animals that are endangered in your state.
Birds Find out where these species live, and mark
the locations on a map of your state.
Reptiles Research the effects of habitat loss on species
in your county or in surrounding areas.
Amphibians

Fishes Portfolio Project

Mollusks and Worms World 30. Endangered Species Outreach Create a spe-
Insects and Crustaceans United States cial project about one endangered species of
your choice. Consider using a poster, an oral
0 50 100 150 200 250 300 presentation, or a video to inform your
Number of identified species classmates about your chosen species or to
persuade them of the importance of saving
the species.

278 Chapter 10 Review