DK THE ECOLOGY BOOK

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ETY

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100 INTRODUCTION

Dutch lens-makers Hans Louis Pasteur reveals Charles Elton publishes
and Zacharias Janssen that wine’s fermentation Animal Ecology, which
invent the compound process is caused by germs;
his discovery sparks the sets out many of the
microscope. development of germ theory. fundamental principles

of animal behavior.

1590 1866 1927
1676 1885

Antonie van Albert Frank coins the
Leeuwenhoek term “mycorrhizae,” in
identifies “animalcules,” reference to the symbiotic
opening up the field relationship between
of microbiology.
fungi and tree roots.

Our understanding of the about them for many years. In trees with the fungi attached
variety, behavior, and the 1860s, French chemist Louis to their roots were healthier than
interraction of organisms Pasteur and German microbiologist those without. The fine filaments,
has advanced considerably since Robert Koch developed the germ or hyphae, of the fungi make the
Aristotle discovered that bee theory of disease, highlighting the roots more efficient at obtaining
colonies have a queen and workers. harmful role played by bacteria. nitrate and phosphate nutrients
Huge advances in technology, Subsequent research has also from the soil. In return, the fungi
field observations, and laboratory highlighted their positive roles: get sugar and carbon from the tree.
experiments have increased our facilitating digestion; inhibiting
knowledge, and the modern study the growth of other, pathogenetic Connected lives
of animal behavior—ethology— bacteria; “fixing” or converting No organism lives in isolation from
continues to throw up surprises. nitrogen into molecules that aid the rest of its ecosystem. The
plant growth; and breaking down behavioral interactions between
Life under the microscope dead organic material, which them are complex and much is still
Until the microscope was invented, releases nutrients for the food web. being discovered about them. One
no one knew that bacteria even of the greatest contributions in this
existed, let alone what they did. Another discovery made field was made by British zoologist
Bacteria were first observed by possible by microscopy was of the Charles Elton, whose 1927 classic
Dutch microscopist Antonie van mutualistic relationship between Animal Ecology established many
Leeuwenhoek in 1676, using fungi and trees, published by important principles of animal
an instrument he had built himself. German plant pathologist Albert behavior, including food webs and
He called these tiny organisms Frank in 1885. Studying what he food chains, prey size, and the
“animalcules,” but little was known first assumed was a pathological concept of ecological niches.
infection, Frank discovered that

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THE VARIETY OF LIFE 101

In Man Meets Insect Thermoregulation In the US, the Human
Dog, Konrad Lorenz by Bernd Heinrich Microbiome Project is
describes the instinctive launched, to map all the
behavior of animals and explains how insects microbes associated with
its evolutionary origins. are able to control their a healthy human body.

own temperature.

1949 1981 2007
1947 1960 2005

David Lack publishes Jane Goodall sets up The first gene mapping
an article on variations a camp in Tanzania to confirms that humans
in bird clutch size as research chimpanzees in share 97–99 percent of
the wild, discovering many their DNA with the other
an evolutionary traits shared by humans.
adaptation. great apes.

Ethology, which looks at animal Field observations are a key tool in a red spot on a parent’s beak when
behavior and its evolutionary basis ethological research. In the 1940s, they want food, will tap colored
and development, is a major British ornithologist David Lack marks painted on a model beak.
component in the modern study investigated the factors controlling
of organisms. Back in 1837, British the number of eggs birds laid Human traits
entomologist George Newport (clutch size). His food limitation As well as these short-term studies,
discovered that moths and bees hypothesis states that the number British primatologist and ethologist
could raise the temperature of their of eggs laid by a species has Jane Goodall conducted field
thorax by quivering their muscles. evolved to match the food available. observations over a longer period,
From the 1970s onward, German- Evolutionary pressure has created studying chimpanzees in Tanzania
American entomologist Bernd a correlation between clutch size from 1960 to 1975. Her findings
Heinrich and others uncovered and food availability. challenged the view that human
more thermoregulatory adaptations behavior is totally unique in the
that have helped insects thrive. Austrian zoologist Konrad animal world, and indicated that
As heterotherms, they are able Lorenz and Dutch biologist Nikolaas chimps are behaviorally closer
to maintain different temperatures Tinbergen also studied animals in to people than had generally been
in different parts of the body. the wild to help understand their assumed. She noted, for example,
behavior. Lorenz’s 1949 work Man that chimps display a whole range
Modern research now combines Meets Dog explains the loyalty of facial expressions and other body
laboratory experiments, field of a pet dog to its owner in terms language to indicate their mood, are
observation, and new technology of canines’ instinctive loyalty toolmakers and users, often behave
such as infrared thermography to their pack leader in the wild. cooperatively, and sometimes go
to understand insect behavior Tinbergen’s field experiments into battle against rival groups. ■
in ever more detail. showed how gull chicks, which tap

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102

ILTTAHISASTTTWWHIOELRMLDIHCARVOEBTEHSE

MICROBIOLOGY

IN CONTEXT M icrobes—bacteria, Scientists did not understand
molds, viruses, protozoa, microbes until they could see them.
KEY FIGURE and algae—are present The first observations began in the
Louis Pasteur (1822–95) in every environment, living in soil, 17th century, using the recently
water, and air. Some microbes invented microscope. These
BEFORE cause disease but most are vital for studies revealed a previously
1683 Dutch amateur scientist life on Earth. Among other things, unknown world teeming with
Antonie van Leeuwenhoek they break down organic matter so microbiotic life. Around the same
uses a microscope to observe that it can be recycled back into time, the word “germ,” originally
bacteria and protozoa. the ecosystem. meaning “seed,” was first used
to describe these tiny organisms.
1796 Edward Jenner carries Trillions of microbes also live on
out the first vaccination, using and in the human body. The most Fighting disease
the cowpox virus to protect common of these microbes are Some 17th and 18th-century
against smallpox. beneficial bacteria, which aid the scientists believed that certain
digestion of food, produce vitamins, “germs” might cause diseases, but
AFTER and help the immune system find the prevailing view was that such
1926 American microbiologist and attack more harmful microbes. maladies were the spontaneous
Thomas Rivers distinguishes result of inherent weakness in an
between viruses and bacteria. Microbes are the worker bees organism. It was not until the
that perform most of the painstaking laboratory work of the
1928 While studying important functions 19th-century French chemist Louis
influenza, Scottish in your body. Pasteur that the “germ theory of
bacteriologist Alexander Dr Robynne Chutkan, disease” was proved.
Fleming discovers penicillin.
Microbiome expert and author Pasteur began by looking at the
2007 An inventory of all alcohol fermentation process. He
the microbes associated discovered that sourness in wine
with a healthy human body was caused by external agents—
is completed. microbes, or germs. A crisis in the
French silk industry, caused by an
epidemic among silkworms, then
allowed Pasteur to isolate and
identify the microorganisms that
caused the particular disease.

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THE VARIETY OF LIFE 103

See also: Classification of living things 82–83 ■ The microbiological
environment 84–85 ■ The ecosystem 134–137

Where observation animal or human, was particularly Louis Pasteur
is concerned, effective at enabling the body’s
immune system to fight off the Born in Dole, France, in 1822,
chance favors only disease. At first, Pasteur faced Pasteur was the son of a poor
the prepared mind. strong opposition and alarm at tanner. He was an average
the prospect, but he was able to student, but he worked hard,
Louis Pasteur develop vaccines for anthrax, fowl obtaining his degree in 1842
cholera, and rabies—the latter and his doctorate in science
As he extended germ theory to involving his first test on a human. in 1847. After teaching in
human disease, Pasteur proposed various universities, in 1867
that germs invade the body and Annihilating germs he became Professor of
cause specific disorders. Edward The focus later shifted to finding Chemistry at the Sorbonne
Jenner, nearly 100 years before, germ-killing agents, or antibiotics, in Paris. His major research
had shown that a disease could be such as penicillin—discovered by interest was the fermentation
prevented with the application of Alexander Fleming. A strategy of process. Pasteur discovered
a “vaccine”—a virus similar to that annihilating microbes has been that the fermentation of wine
of the disease-causing microbe. followed ever since. Yet this and beer was caused by
Pasteur found that an attenuated, “slash and burn” approach has germs—microbes. He also
or weakened, form of a disease- its drawbacks. It kills beneficial discovered that microbes
causing germ, produced in a microbes as well as harmful ones, could be killed by short, mild
laboratory and injected into the host and also promotes resistance in heat treatment—a process
bacteria that can ultimately render now named after him as
antibiotics ineffective. ■ “pasteurization.” Pasteur’s
“germ theory” led to the wider
The bacterium Enterococcus faecalis development of vaccines,
is a microbe found in the gut and bowel which remain a vital method
of healthy humans. If it spreads to other of disease control. In 1887,
areas of the body, however, it can cause he established the Pasteur
serious infections. Institute, which opened in
1888 and continues to help
prevent and fight diseases.

Key works

1870 Studies on Silk Worm
Disease
1878 Microbes: Their Role in
Fermentation, Putrefaction,
and the Contagion
1886 Treatment of Rabies

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104

HCWAEIVRTETHAAFINUSNYTMGRIEBEIOSSPISECIES

THE UBIQUITY OF MYCORRHIZAE

IN CONTEXT I n 1885, a professor of plant
pathology at the Royal College
KEY FIGURE of Agriculture in Berlin named
Albert Frank (1839–1900) Albert Frank was the first to see a
connection between fungi growing
BEFORE on tree roots and the health of the
1840 German botanist trees. Frank realized that these were
Theodor Hartig discovers not pathological (disease-related)
a network of filaments on the infections but in fact underground
roots of pine trees. partnerships: far from suffering, the
trees seemed to benefit from better
1874 Hellmuth Bruchmann, nutrition. He invented a new term
a German biologist, notes for the partnership—“mycorrhiza,”
the “Hartig net” is made of from the Greek mykes, meaning
fungal filaments. fungus, and rhiza, meaning root.

AFTER Mycorrhizae in action Mycorrhizae on the root of a
1937 A.B. Hatch, an American False truffles are an example of soybean. In arbuscular mycorrhizae,
botanist, shows a beneficial the fungal side of this partnership. such as these, the tips of the hyphae
relationship between pine Nineteenth-century Prussian form clusters inside the plant’s root
trees and mycorrhizal fungus. botanists had found these fungi cells, optimizing nutrient exchange.
under spruce trees, and noticed
1950 Swedish botanists Elias that each tree root was drawn absorb the soluble organic
Melin and Harald Nilsson toward a truffle, and wrapped in compounds produced through a
show that plant roots can a fungal husk. Although they did network of microscopic filaments—
extract more nutrients from the not know it, the botanists were hyphae—called a mycelium.
soil with the aid of mycorrhizae. witnessing a phenomenon that
is vital to many ecosystems. Plants rely on root hairs to
1960 Another Swedish absorb water and minerals, such as
botanist, Erik Björkman, shows Fungi are typically nourished nitrates and phosphates. But there is
that plants pass carbon into by a supply of organic matter, from a limit to how far plant roots can
mycorrhizal fungi in exchange which they extract food by external grow and therefore what quantity of
for phosphate and nitrate. digestion. A deep layer of forest nutrients the root hairs can absorb.
litter is perfect. They pour digestive The hyphae of mycorrhizae can
chemicals onto their meal and cover a much wider area, absorbing

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THE VARIETY OF LIFE 105

See also: Evolution by natural selection 24–31 ■ Mutualisms 56–59 Mycorrhizae as
■ The ecosystem 134–137 ■ Energy flow through ecosystems 138–139 pollution indicators

Beneficial exchange between Mycorrhizal fungi are not only
mycorrhizae and plant roots good for the health of plants—
they can also act as indicators
Mycorrhiza Supplies sugar from Plant of the health of the entire
photosynthesis environment. Laboratory
experiments with these fungi
Connects plants in an have shown that some grow
extensive network badly in the presence of toxins,
which means that they can be
The mutualistic Increases uptake of used to detect pollutants in
relationship between water and nutrients the air or soil. For instance,
mycorrhizae and plants some fungi fail to grow when
is highly evolved. As Allows plants to share exposed to heavy metals such
many as 90 percent of nutrients with others as lead or cadmium, and
all plant species rely on because different kinds of
fungi for nutrients and Boosts protection fungi react differently to
protection. In return, against soil diseases environmental change, certain
plants supply the fungi species can be used to identify
with a vital food source. specific kinds of pollution.

a much greater amount of minerals. fungi in this way. Trees supported Mycorrhizae are also useful
When the fungal hyphae attach to by mycorrhizae are more resistant indicators of the health of their
the plant roots, they extend the root to drought and disease, and can native habitat. Many form
system, causing extra nutrients to even communicate alarm signals by cauliflower-like growths
seep into the plant. releasing chemicals in response to on tree roots, but these are
attack by herbivores. This fungal smaller in polluted soil. The
Albert Frank realized that this network connecting trees has been trees themselves may also
partnership worked both ways. It dubbed “the wood-wide web.” ■ respond to pollution with
was a winning combination for both weaker shoot growth, but
plant and fungus. In exchange for [the fungus] performs the mycorrhizal response is
passing on a share of its minerals, a “wet nurse” function more acute and serves as a
the fungus receives sugar from the valuable early-warning sign
plant—made by photosynthesis in and performs the of a habitat in decline.
the leaves and transported to the entire nourishment
roots via the plant’s sap. This boosts Weak growth in the russet
the nutrient supply that the fungus of the tree from brittlegill, a mycorrhizal fungus
derives from dead organic matter. the soil. of European and North American
spruce forests, can be an early
Ancient networks Albert Frank indicator of habitat air pollution.
Fossils of plants dating from 400
million years ago—when vegetation
was first spreading across dry
land—show traces of fungal threads.
This suggests that the mycorrhizal
partnership was key to the evolution
of terrestrial life. Today, the majority
of plant species continue to rely on

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BFQOUUOERDSNISTIINTOHGNE

ANIMAL ECOLOGY

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108 ANIMAL ECOLOGY

IN CONTEXT The concept of food chains— knowledge of individual plant and
the idea that all living animal species to the cells in a
KEY FIGURES things are linked through beehive—each “cell” of knowledge
Charles Elton (1900–91), their dependence on other species is important in its own right, but
George Evelyn Hutchinson for their food—dates back many by putting them all together
(1903–91) centuries, but it was not until the something much more than the
early 20th century that scientists sum of the parts is created—
BEFORE developed the concept of food the “beehive” of ecology.
Ninth century Arab writer chains forming a food web.
Al-Jaziz introduces the Nowadays, the study of animal
concept of the food chain The pioneer of this thinking was ecology focuses on how animals
in Kitab al-Hayawan (Book British zoologist Charles Elton, interact with their environment,
of Animals), concluding that whose book Animal Ecology (1927) the roles played by different
“every weak animal devours describes what he called the “food species, why populations rise
those weaker than itself”. cycle”. He later went on to develop and fall, why animal behaviour
theories that encompassed more sometimes changes, and the
1917 American biologist complex interactions between impact of environmental change on
Joseph Grinnell first describes animals and the environment— animals. The principle underlying
an ecological niche in his insights that underpin modern the work of animal ecologists is
paper, “The niche relationships animal ecology. He likened our that there is generally a balance
of the California Thrasher.”
Food web
AFTER
1960 American ecologist and Whale Albatross
philosopher Garrett Hardin Arrow worm
publishes an essay in the Krill Schooling fish Leopard
magazine Science in which Phytoplankton seal
he states that “every instance
of apparent coexistence must Blue-green Radiolarians
be accounted for.” bacteria

1973 Australian ecologist Penguin
Robert May publishes Stability
and Complexity in Model
Ecosystems, in which he uses
mathematical modeling to
demonstrate that complex
ecosystems do not necessarily
lead to stability.

Copepod Dolphin
Marine worm
Squid

A food web is a graphic depiction Killer whale
of the feeding connections between
different species within an ecological Seaweed Bottom-feeding
community. This example illustrates fish
the relationships within a marine
ecosystem, in which killer whales are
the apex predators and phytoplankton
are the primary producers.

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THE VARIETY OF LIFE 109

See also: Keystone species 60–65 ■ The food chain 132–133 ■ The ecosystem Forecasting the effects
134–137 ■ Energy flow through ecosystems 138–139 ■ Trophic cascades 140–143 of climate change

in nature, so if the population Ecologists examine changes
of a given species grows too large to animal populations and
it will be regulated, most often by a distribution and apply climate
lack of food. However, relationships change models to forecast how
between organisms and their these will change further in
environment change from place the future, over the course of
to place and through time. 5, 10, 50, or more years. In the
Arctic, for example, where
Chain of dependence A spider traps a damselfly, average temperatures are
In Animal Ecology, Elton outlined demonstrating that the principle rising more rapidly than
the key principles of the study of of food size can be modified by the anywhere else, the sea ice is
animal communities: food chains comparative aggression and strength contracting. As a result, polar
and webs, food size, and ecological of the predator and its prey. bears have to travel farther in
niches. Each food chain and web, search of ice where they can
he asserted, is dependent on against rivals of their own species catch seals, rest, and mate.
producers: plants and algae that to ensure there is enough food for The farther they swim, the
support plant-eating consumers themselves and their offspring. more energy they burn. As
(herbivores). These herbivores in the sea ice declines, the polar
turn support one or more levels of Food size bears starve. Scientists
meat-eating consumers (carnivores). One of Elton’s most important monitor their numbers and
Large carnivores generally eat points was the notion that food movements and compare this
smaller animals, but because small chains exist primarily because data with changes in sea ice.
animals reproduce more quickly, of the principle of food size. He
their numbers are able to support explained that every carnivorous The polar bear plays a
the larger predators. animal eats prey between upper vital part in the ecology of the
and lower limits. Predators are Arctic. As an apex predator
Competition for food is very tight physically unable to catch and and keystone species, it must
near the top of a food web. Although consume other animals above a have access to seals, which
apex (top) predators, such as big certain size because they are not are its almost exclusive diet.
cats and large birds of prey, have no large enough, strong enough, or The number of seals regulates
natural predators, this often means skillful enough. That is not to say the density of polar bears,
that they have to defend territories that predators cannot kill and eat while polar bear predation in
larger animals than themselves; a turn regulates the density and
Every animal is closely weasel can easily kill a larger rabbit reproductive success of seals.
linked with a number of because it is more aggressive.
However, an adult lioness, one A lone polar bear surveys the
other animals living of the world’s top predators, is not sea for prey from a piece of floating
around it—and these are capable of killing a healthy adult ice in the Arctic. The shrinking
African elephant. Likewise, area of sea ice in the region
largely food relations. a dragonfly larva on the bottom threatens this species’ survival.
Charles Elton of a pond may be able to prey
on a small tadpole, but it would
not be able to eat an adult frog. ❯❯

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110 ANIMAL ECOLOGY

Snowshoe hare and The Sword-billed Hummingbird,
lynx population cycles a native of South America, has a long
bill, which enables it to suck up nectar
In Canada’s boreal forests, from the long flowers of Passiflora
the favored prey of lynx are mixta, a species of passionflower. As
snowshoe hares. Charles Elton it feeds, it spreads the plant’s pollen.
examined the relationship
between the populations Animals may be capable of killing working in the early decades of the
of these two species, using much smaller prey, but it is simply 20th century, an organism’s niche
data covering the period not worth the effort. Wolves hunt was defined as its habitat. He
1845–1925. When hares are medium-sized or large mammals studied birds called thrashers in
numerous, lynx hunt little such as elk. If those mammals California and observed how they
else. After their population disappear from their environment, fed, nested, and hid from predators
reaches its peak density, they find it hard to catch sufficient in the dense undergrowth of the
the hares struggle to find numbers of smaller animals such chaparral shrubland. However, a
enough plant food. Some as mice to sustain them; the niche is more complex than simply
starve, while others are energy they use finding small prey the place where an organism lives.
weakened and are more is greater than the energy they Oxpeckers and buffalo share exactly
easily caught by predators, gain by consuming them. the same habitat—open grassland –
including lynx, which feed but their requirements for survival
very well for a time. When Plants cannot run away or fight are very different: the buffalo graze
hare numbers continue to back, so different considerations on the grasses, while oxpeckers
fall, this affects the lynx. apply to herbivores when it comes derive their food from the ticks they
They are forced to hunt to food size. There is a maximum peck from the buffalos’ hide.
less nutritious prey, such size of seed that a given finch,
as mice and grouse. for example, can fit in its bill, so Charles Elton explored the
larger finches have an advantage concept of ecological niches in
As they struggle to find over smaller species. Similarly, more depth. For him, food was
enough to eat, lynx produce individual species of hummingbirds the primary factor in defining an
smaller litters or even stop can drink nectar only from flowers animal’s niche. What it ate and
breeding altogether. Some up to a certain size, depending what it was eaten by were crucial.
starve to death. A decline in on the length of their bill. Depending on the habitat, a
the lynx population sets particular niche could be filled by
in one or two years after the a different animal. Elton cited the
hare population has bottomed example of a niche that was filled
out, a cycle that repeats every
eight to eleven years. Observation of species in the
wild convinces me that the
existence and persistence of
species is vitally bound up

with environment.
Joseph Grinnell

A Canadian lynx captures a Ecological niches
snowshoe hare, its preferred prey. An animal or plant’s niche is its
When hares are plentiful, a lynx ecological role or way of life. For
will eat two every three days. American zoologist Joseph Grinnell,

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THE VARIETY OF LIFE 111

Different species press interacts with other organisms and example, koalas depend almost
against one another, like with its environment. For example, entirely on eucalyptus leaves, and
soap bubbles, crowding each species of trout—and other Hyacinth Macaws in the Pantanal
fish—has its own range of water region of Brazil eat virtually nothing
and jostling, as one salinity, acidity, and temperature but the hard fruits of two species of
species acquires … some that it can tolerate, as well as a palm trees—these are specialists.
advantage over another. range of prey and river- or lake-bed
G. Evelyn Hutchinson conditions. This makes some better Animals rarely occupy the whole
competitors than others, depending of their niche width, owing to
by birds of prey that hunted small on the conditions of the habitat in competition between species. Part
ground-dwelling animals such as which they live. Seen as the father of the habitat requirement of North
mice and voles. In a European of modern ecology, Hutchinson American bluebirds is dead trees
oakwood, that niche would be filled inspired other scientists to explore with old woodpecker holes in which
by Tawny Owls, while on open how competing animals use their they lay their eggs and raise their
grassland Kestrels would fill the role. environment in different ways. young. Although suitable holes are
common in many forests, bluebirds
Elton also argued that an animal An animal or plant’s niche cannot occupy all these holes
could not only tolerate a certain set width comprises the whole range because they are often out-
of environmental conditions, but of factors it requires to allow it to competed by more aggressive
could also change them. The tree- thrive. Brown rats, raccoons, and starlings. Therefore their realized
felling and stream-damming starlings are examples of animals niche—the places they actually
activity of beavers is one of the with a broad niche width in that occupy—is not as extensive as their
most dramatic examples, creating they are able to survive in a wide potential (or fundamental) niche.
habitats for fish in dammed pools, variety of conditions. Such species
woodpeckers in dead trees, and are called generalists. Other animals Many animals share some
dragonflies around pool margins. have narrow requirements. For aspects of their niche, but not
others. This is called niche ❯❯

Niches and competition
British-born zoologist G. Evelyn
Hutchinson, working at Yale
University from the 1950s to the
1970s, examined all the physical,
chemical, and geological processes
at work in ecosystems and
proposed that any organism’s role
in its niche includes how it feeds,
reproduces, finds shelter, and

A true specialist, a koala bear
requires 2.5 lb (1kg) of eucalyptus
leaves a day. This species is found
in the wild only in Australia, where
eucalyptus is common.

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112 ANIMAL ECOLOGY

Three major overlap. If different species live in
types of ecological the same habitat and have similar
lifestyles, they will be in
pyramid competition but they may be able
to live in close proximity if some
Pyramid 1 aspects of their behavior or diet The basic process in
of numbers Osprey differ. This arrangement is known trophic dynamics is the
as niche partitioning. For example, transfer of energy from
10 various anole lizards on Puerto one part of the ecosystem
Northern pike Rico successfully occupy the same
areas because they select perching to another.
100 locations in different parts of trees. Raymond Lindeman
Perch
There are limits to niche numbers to produce a pyramid
1,000 overlap. When two animals with of biomass that represented the
Bleak identical niches live in the same amount of living matter in a given
place, one will drive the other area at every level. This took
10,000 to extinction. This concept—the into account the fact that some
Freshwater shrimp competitive exclusion principle— organisms are much larger than
was outlined by Joseph Grinnell others, but because it showed
Pyramid Wolf in 1904 and developed in a paper comparative biomasses at a fixed
of biomass 340 lb published by Russian ecologist point in time, it produced anomalies.
per sq mile Georgy Gause in 1934, becoming For example, in a pond, the mass
Red fox known as Gause’s law. of the phytoplankton producer
1,700 lb (microscopic organisms that are the
per sq mile Pyramid of numbers foundation of the aquatic food web)
Charles Elton used a pyramid as may not be as great as the mass of
Snowshoe hare a way of graphically representing the fish consumers at a particular
17,000 lb per sq mile the different levels in a food chain, point in time, so the pyramid
with the producers at the bottom, will be inverted. However,
Grass the primary consumers on the phytoplankton reproduce quickly
18 million lb per sq mile level above, and so on. Often, the
primary consumers—insects,
Pyramid Apex in particular—will outnumber the
of energy predators producers, but the higher levels
of consumers will become less
0.01% numerous toward the top of the
Secondary pyramid. This system does not
carnivores take account of parasites; fleas
and ticks on mammals and birds
0.1% will far outnumber the total of all
Carnivores the vertebrates in an ecosystem.

1% In 1938, German-born animal
ecologist Frederick Bodenheimer
Herbivores modified Elton’s pyramid of
10%

Producers
100%

Ecological pyramids represent Microscopic organisms, including
quantifiable data in an ecosystem. these diatoms, form a significant part
Numbers show the population size of of all ecological pyramids. Their huge
individual species in a trophic level; numbers and rapid reproduction
biomass, their relative presence; and provide mass and energy for the
energy, who eats what and how much. species higher up the pyramid.

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THE VARIETY OF LIFE 113

when conditions, such as sunlight herbivore, some of the energy Tench feed on snails, which graze
and nutrients, are right. Over time, transfers to the animal. When on periphyton—a mixture of microbial
the mass of the phytoplankton will a predator eats the herbivore, organisms that cling to plants. By
far outweigh that of the fish. it receives a smaller amount of that reducing the number of snails, tench
energy, and so on. increase the periphyton biomass.
Trophic pyramids
American ecologist Raymond Published in 1942, Lindeman’s above. Assessing energy transfer,
Lindeman proposed a pyramid of Ten Percent Law explains that however, requires a lot of information
energy, called the trophic pyramid, when organisms are consumed, about energy intake, as well as the
showing the rate at which energy only about 10 percent of the energy number and mass of organisms.
is transferred from one level to the transferred from them is stored as
next as herbivores eat plants, and flesh at the next trophic level. The Future thinking
predators eat herbivores. An energy model creates a more Relationships between organisms
organism’s trophic level is the realistic picture of the condition and their environment change
position it occupies in a food chain. of an ecosystem. For example, if from place to place and through
Plants and algae are at trophic level the biomass of weed and fish in time. Global climate change is one
1, herbivores at level 2, and the first a pond is the same, but the weed example of environmental factors
level of predators is at 3. It is rare reproduces twice as fast as the fish, that will increasingly affect animal
for there to be more than five levels. the energy of the weed would be communities. Some changes have
Plants convert the sun’s energy shown to be twice as large. Also, already taken place, but one of the
into stored carbon compounds, there are no inverted pyramids— challenges of ecological thinking
and when a plant is eaten by a there is always more energy in the in the future is to forecast others. ■
lowest trophic level than the one

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114

BOOTHIFFREEODGOFSGFPLSSTAPIMTYRHUITNAMHTGENPNURUMOMDBBUEECRRE

CLUTCH CONTROL

IN CONTEXT W hy do some birds lay eggs are removed from a nest; the
more eggs than others? bird will re-lay repeatedly to
KEY FIGURE For example, Blue Tits compensate for the loss.
David Lack (1910–73) lay nine eggs, Northern Flickers six,
and Robins four. In the 1940s, Instead, Lack said, the number
BEFORE British ornithologist and evolutionary of eggs laid by any species has
1930 British geneticist ecologist David Lack proposed an evolved to fit with the food supply
Ronald Fisher combines explanation that rapidly gained available. In other words, nature
Gregor Mendel’s work on support. He argued that the clutch favors clutch sizes that correspond
genetics with Charles size (number of eggs laid) was not to the maximum number of young
Darwin’s theory of natural controlled by the female’s ability to
selection, and argues that the lay eggs, since birds can lay many Blue Tit nests contain an average of
effort spent on reproduction more eggs than they typically do. nine eggs, although the females can lay
must be worth the cost. This fact can be demonstrated by many more. David Lack proposed that
replacement experiments, in which the clutch size is determined by the
AFTER likely amount of available food.
1948 David Lack extends his
theory of optimal clutch size
in birds to include litter size
in mammals.

1954 Lack develops his food
limitation hypothesis further
in The Natural Regulation
of Animal Numbers, to
encompass birds, mammals,
and some insect species.

1982 Tore Slagsvold proposes
the nest predation hypothesis,
which states that clutch size
is related to the likelihood of
the nest being attacked.

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THE VARIETY OF LIFE 115

See also: Animal ecology 106–113 ■ Animal behavior 116–117 ■ The food chain Siblicide and the
132–133 ■ The ecosystem 134–137 ■ Ecological resilience 150–151 Blue-footed Booby

that the parents are likely to be able Laying a clutch which Blue-footed Boobies are
to sustain. So, if a pair of birds can will result in a smaller seabirds native to the Pacific
only find enough food to feed six brood than … could be fed Ocean. They get their food
chicks, but the female has laid 12 and reared successfully … from the ocean, but come
eggs, those young will be hungry confers advantages. to rocky shores and cliffs to
and may starve. If she has laid just breed. The female lays two
one egg, although the chick will Tore Slagsvold eggs, roughly five days
be raised successfully, most of apart, so that by the time the
the available food will have been of food during the long day-length second chick hatches, the first
unused. So neither the 12-egg nor of summer compared with the one has already grown
the one-egg scenarios are good shorter day-length in the tropics. considerably. When food is
reproductive strategies; instead, plentiful, the parents can find
laying six eggs offers the best However, other factors may enough to feed both offspring
chance of raising the most offspring. also apply. Higher mortality rates until they fly the nest (fledge).
in high latitudes—where winters However, when food is scarce,
This theory became known as are harsh—may have led to the the larger chick will peck its
the food limitation hypothesis, or evolution of large clutch sizes. This junior sibling to death. The
Lack’s principle, and it was later is because the chances of survival older chick can then get more
generalized by him and others to until the next breeding season food, and is more likely to
cover litter size in mammals and are low, and the reduced population fledge. If it does not murder
clutch size in fish and invertebrates. results in more food being available its sibling when food is scarce,
for the survivors next season. both chicks may starve.
The “latitude trend”
Lack’s hypothesis also suggested In 1982, Tore Slagsvold, a This behavior, based
an answer to another puzzle: why Norwegian evolutionary ecologist, exclusively on the availability
most bird species have bigger advanced the nest predation of food, is called “facultative
clutches at higher latitudes. On hypothesis, which proposes that siblicide.” In contrast, masked
average, birds near the equator lay high rates of nest predation result boobies practice “obligate
about half the number of eggs laid in smaller clutches. If a nest with siblicide”—the first-hatched
by the same species in the far many chicks is found by a predator, chick nearly always kills its
north. This “latitude trend” could be more work by the parent birds will brother or sister, regardless
explained by a greater availability have been wasted than if the nest of how much food is available.
contained fewer chicks. Also,
Clutch size increases parents raising a large clutch are Blue-footed Boobies are driven
with increasing latitude more likely to be seen by predators, to siblicide by genetic factors.
and day length because … because of the extra activity. Some The murder of a sibling can benefit
a longer day enables the ecologists have argued that the the perpetrator while also ensuring
parents to find more food. relative abundance of predators in the survival of the entire species.
the tropics has been more important
David Lack than food supply in the evolution of
small clutch sizes at low latitudes. ■

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116

DCTTHHOANEEG TBEISIOVEENASRSDOBLWFEAITSTHTHIISNAGETARARUSTEH

ANIMAL BEHAVIOR

IN CONTEXT A ny dog owner will describe Ducklings imprinting is an example
the companionable and of instinctive behavior that can be
KEY FIGURES loyal relationship they manipulated—to make them imprint
Konrad Lorenz (1903–89), enjoy with their pet. The Austrian on humans or even inanimate objects.
Nikolaas Tinbergen zoologist Konrad Lorenz set out
(1907–88) to explain this behavior in Man when devising rigorous field
Meets Dog (1949). He described the experiments that could be repeated,
BEFORE behavior of dogs and other pets as so that the findings could be
1872 Charles Darwin’s The substantially innate, “instinctive recognized as facts, not anecdotes.
Expression of the Emotions in activity,” as opposed to behavior
Man and Animals posits that learned through conditioning. The term “ethology” was coined
behavior is instinctive and has Lorenz proposed that such hard- by American entomologist William
a genetic basis. wired behavior helped the animal Morton Wheeler in 1902 to describe
survive as a species. For example, a the scientific study of animal
1951 Nikolaas Tinbergen’s domestic dog’s loyalty to its human behavior. Ethologists study animals
The Study of Instinct lays master originates in the natural in their natural habitats, combining
down the foundations and behavior of its wild ancestors, laboratory studies and fieldwork
theory behind ethology, the which were loyal to the pack leader in order to describe an animal’s
study of animal behavior. because this had benefits in terms behavior in relation to its ecology,
of hunting success and safety. evolution, and genetics.
AFTER
1967 Desmond Morris, Field experiments Ethologists found that in certain
a British zoologist, brings Lorenz was not alone in his theories. situations, an animal will have a
ethology to bear on human Other biologists working in the field predictable behavioral response.
behavior in his popular book included fellow Austrian Karl von They called this a “fixed action
The Naked Ape. Frisch and Dutch biologist Nikolaas
Tinbergen, who studied animals
1976 British evolutionary in their natural environments. Until
biologist Richard Dawkins then, most animal behavior studies
publishes The Selfish Gene, had taken place in laboratories or
describing how most of an artificial settings, so the behavior
animal’s behavior is designed witnessed was not entirely natural.
to pass on its genes. Studying animals in the wild had
its own challenges, particularly

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THE VARIETY OF LIFE 117

See also: The selfish gene 38–39 ■ Field experiments 54–55 ■ Keystone species 60–65 ■ Animal ecology 106–113 ■ Clutch
control 114–115 ■ Using animal models to understand human behavior 118–125 ■ Thermoregulation in insects 126–127

pattern” (FAP). A FAP has set Four elements of ethological experimentation
characteristics. It is species-
specific; it is repeated in the same Causation Development
way every time and is not affected What triggered What stage is the animal
by experience. The triggers for the the behavior in in its life cycle, and does the
behavior (“sign stimuli”) are highly the first place?
specific and may involve a color, behavior change as
pattern, or sound. For example, male the animal develops?
sticklebacks respond aggressively
when another male enters their When studying
streambed patch. Ethologists animal behavior,
suggest this is triggered by seeing scientists consider
the male’s red underbelly. these four elements

Nikolaas Tinbergen found Evolution Function
that some an artificial sign stimuli How is the behavior How does the behavior
work better than the real thing. He related to the animal’s increase the animal’s
investigated the begging behavior evolution or ancestry?
of herring gull chicks, which peck chance of survival or
at a red spot on the parent gull’s reproductive success?
beak to make it regurgitate food.
He found that chicks will also peck
at a model of the gull’s beak, yet
when they were offered a narrow
red pencil with three white lines
at the end, the chicks pecked at
this even more enthusiastically.
Tinbergen called this a
“supernormal stimulus,” showing
that instinctive animal behavior
can be manipulated artificially. ■

Konrad Lorenz Born in Vienna, Austria, Lorenz and other birds, as well as
was enthralled by animals from mammals, is instinctive and
an early age and kept fish, birds, occurs shortly after birth. Lorenz
cats, and dogs. The son of an demonstrated the theory by
orthopedic surgeon, he studied quacking like a duck at newly
medicine at Vienna University, hatched ducklings. He soon
graduating in 1928, and gained had a flock of ducklings that
his Ph.D. in zoology in 1933. His followed him everywhere.
numerous pets became the first
subjects of his studies. Lorenz is Key works
perhaps best known for describing
the phenomenon known as 1952 King Solomon’s Ring:
“imprinting.” This is when a New Light on Animal Ways
newly hatched chick bonds with 1949 Man Meets Dog
the first thing it sees (usually its 1963 On Aggression
parent) and will follow it around. 1981 The Foundations for
The behavior, seen in ducks Ethology

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REDEFINE “TOOL,”

AS HUMANSCHIMPANZEESREDEFINE “MAN,” OR ACCEPT

USING ANIMAL MODELS TO UNDERSTAND
HUMAN BEHAVIOR

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120 USING ANIMAL MODELS TO UNDERSTAND HUMAN BEHAVIOR

IN CONTEXT The Primates Tree

KEY FIGURE 750,000–550,000 ya Humans and their
Jane Goodall (1934–) 6 mya closest relatives,
BEFORE chimpanzees, are both
1758 Carl Linnaeus, the father primates. This shows
of taxonomy, dares to classify how primates have
humans within the rest of evolved over the last
nature, calling us Homo 66 million years.
sapiens (“wise man”).
1859 Charles Darwin’s 35 mya Great
theory of evolution further 40 mya apes
challenges the established Lesser
view that man is different apes
from the animal kingdom. Old world
AFTER monkeys
1963 Konrad Lorenz publishes New world
On Aggression, proposing monkeys
that warlike behavior in
humans is innate. Primates
1967 Desmond Morris,
a British zoologist and 65 mya
ethologist, publishes The
Naked Ape: A Zoologist’s Modern Neanderthal Gorilla Chimpanzee/ Orangutan
Study of the Human Animal, human Bonobo
a major study that describes
human behavior in the Gibbon Monkey Baboon Tarsier Lemur Loris
context of the animal kingdom.
M odern molecular studies scientific community remained
In reality, we are Pan narrans, mapping the genomes convinced that humankind was
the storytelling chimpanzee. of humans and other different from the rest of nature.
animals have confirmed a theory
Terry Pratchett that was first suggested by Charles It was largely the work of British
Darwin in the mid-19th century— primatologist Jane Goodall that
British fantasy author that we share a common ancestor opened our eyes to the similarities
with the great apes. Today, few between chimps and man. In 1961,
scientists would dispute that the in an excited communication
common chimpanzee (Pan to her mentor, Louis Leakey,
troglodytes) and the bonobo or Goodall announced an observation
pygmy chimpanzee (Pan paniscus) that would shake the scientific
are our closest living relatives. The establishment: she had seen
study of these animals therefore a chimp using a tool. It was the
offers us a unique chance to learn first time this behavior had
about ourselves and the origins of been documented and it would
our behavior. Yet for many years the challenge perceived ideas of what
it means to be human.

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THE VARIETY OF LIFE 121

See also: Evolution by natural selection 24–31 ■ A system for identifying all nature’s organisms 86–87 ■ Animal ecology
106–113 ■ Animal behavior 116–117

Goodall’s knowledge of natural
history had impressed Leakey
on their first meeting in 1957 and
he offered her a job studying the
behavior of chimpanzees. As an
anthropologist and paleontologist,
Leakey believed in evolutionary
theory, which proposed that humans
and the great apes—chimpanzees,
bonobos, gorillas, and orangutans—
in the family Hominidae (Great
Apes), share a common ancestor.

Making connections Until this point, the scientific and A chimp uses a twig stripped of its
Leakey’s fieldwork focused on popular consensus was that the leaves—a modified “tool”—to catch
looking for the “missing link”— ability to devise and make tools termites for consumption. Goodall first
fossils of transitional forms marked humans out as superior recorded the ability of chimpanzees to
between that common ancestor to the rest of the animal kingdom. invent simple technologies in Gombe.
and humans. Chimpanzees had not Goodall’s findings forced scientists
been studied seriously in the wild to think again. true unfettered behavior, Goodall
and such a study, he reasoned, was one of the first people to work
could throw light on the evolution Goodall’s camp was in Gombe in the field of ethology, whereby
of early humans. Goodall, a keen Stream National Park, Tanzania, biologists monitor animals in their
observer and free of academic ties, where she studied a chimp natural environments and try to
was the ideal choice for the work. community on the eastern shore understand their natural behaviors.
As Leakey had hoped, she provided of Lake Tanganyika. In choosing to In her first few months at the ❯❯
a fresh perspective on the theory live among chimps to witness their
and was brave enough to say that
chimps and humans were more
alike than had been imagined.

Jane Goodall Born in London in 1934, Jane transformed our understanding
Goodall’s first meeting with a of chimpanzees and challenged
chimp was a stuffed animal that perceived ideas of our own place
her father named Jubilee. She was in the natural world. In 1965, she
interested in animal behavior from earned a Ph.D. in ethology from
an early age—once, she hid in a Cambridge University. Her many
henhouse for hours so that awards include France’s Legion
she could watch a chicken lay of Honor, given to her in 2006.
an egg. She left school at 18 and
worked in various jobs, before Key works
going to Kenya in 1957 and
meeting paleoanthropologist 1969 My Friends the Wild
Louis Leakey. With his support, Chimpanzees
in 1960 Goodall set up a research 1986 The Chimpanzees of
base in Gombe, Tanzania, where Gombe: Patterns of Behavior
she was to study chimpanzees 2009 Hope for Animals and
until 1975. Her work radically Their World

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122 USING ANIMAL MODELS TO UNDERSTAND HUMAN BEHAVIOR

camp, the chimps fled from her, and then using them in termite Jane Goodall working, notebook in
but they then began to forget she mounds; the chimps were not only hand, at Gombe National Park in 2006.
was there. using tools but making them. The pioneering primatologist continues
her lifelong commitment to protect
Goodall sat for many hours Chimp technology endangered chimpanzees.
observing the chimps, keeping her Goodall went on to witness nine
distance and quietly making field different tools being used by instead of numbers, suggesting
notes. One morning in November chimps in the Gombe community. that her fieldwork was less than
1961, she noticed a chimpanzee she At the time, scientists questioned rigorous. Since then, however, many
called David Greybeard sitting over Goodall’s methods and ridiculed other studies around the world have
a termite mound. He was poking her for giving the chimps names corroborated her findings: chimps in
blades of grass into the mound, the Congo have been observed
pulling them out, and then putting I viewed my stripping twigs to use in termite
them into his mouth. She watched fellow man not mounds; chimps in Gabon have
for some time before the chimp as a fallen angel, been seen heading into the forest
moved off. On reaching the spot but as a risen ape. with a five-piece “toolkit” that
where the chimp had been sitting, Desmond Morris included a heavy stick for opening
Goodall saw discarded grass stems bee hives and pieces of bark for
lying on the ground. Picking one up British Zoologist scooping up the honey. In Senegal,
and poking it into the mound, she hunting parties of chimps have been
found that the agitated termites bit observed traveling with sticks that
onto the stem. She realized the they chew to a sharp point and use
chimp had been “fishing” for like spears to kill bush babies.
termites with the grass stems, and
transferring them into his mouth. More alike than different
Ethologists take behaviors studied
From talks with Leakey, Goodall across several species to formulate
knew this was a major discovery. generalizations that apply to many
She also saw chimps modifying thin
twigs by stripping them of leaves

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THE VARIETY OF LIFE 123

We admit that we it is worth noting that these Chromosomal
are like apes, but percentages are based on genes evidence
we seldom realize that instruct the body how to make
that we are apes. proteins, which make up a very A strong piece of evidence
Richard Dawkins small part of the human genome in favor of a shared common
(about 2 percent). It is likely that the ancestor is seen by comparing
British evolutionary biologist things that make humans different chromosomes. Chimpanzees
from chimpanzees can be found in (and gorillas) have 24 pairs of
species. The idea that animal the regions of DNA called “junk chromosomes. Humans have
behavior could be a model for DNA” because they were previously only 23. Evolutionary scientists
human behavior took root in the thought to be redundant. It is now believe that when we diverged
work of ethologists in the 1950s and understood that this junk DNA from a common ancestor, two
’60s, such as Konrad Lorenz, holds vital information about how chromosomes in humans
Nikolaas Tinbergen, and Karl von and when genes are expressed. fused and this is why we have
Frisch. Studying animals in their Still, the similarities between the one less pair than other apes.
natural habitats, they saw how DNA of humans and the great apes
complex the lives of animals were. are striking. On the ends of every
They began to understand social chromosome, there are genetic
interactions arising from instinct Meat-eating hunters markers—or sequences of
as well as learned behaviors. The During her studies, Goodall also DNA—called telomeres. In the
animal studies held a mirror up witnessed chimps eating meat middle of each chromosome
to human behaviors. and hunting. As with tool-making, there is a different sequence,
the idea that chimpanzees were known as a centromere. If
The persistent belief that carnivorous predators went against two chromosomes have fused,
humans are totally different from all received knowledge. At first, it should be possible to see
other species was firmly rebutted scientists claimed it was aberrant telomere-like regions in the
with the advent of gene mapping. behavior, but as the research middle of the chromosome as
When the chimpanzee genome was continued and more sightings were well as at each end. Also, the
mapped in 2005—followed by the made, it became established fact. fused chromosome would have
other great apes—and compared Meat-eating has been reported in two centromeres. Scientists
with the human genome, the just about every area where chimps looked and found just this.
results were clear. Humans share have been studied, from Gombe Human chromosome 2 appears
98.8 percent of their DNA with and Mahale Mountains National to be the fusion of chimp
chimps, 98.4 percent with gorillas, Park, Tanzania, to Tai National chromosomes 2a and 2b. It is
and 97 percent with orangutans. Park, in Côte d’Ivoire. ❯❯ almost beyond doubt that we
Humans and great apes are more share a common ancestor with
alike than they are different. Yet chimps, bonobos, and gorillas.

An alpha male’s body language
says “keep away” to begging chimps
wanting a share of his prey in Gombe
National Park. The main source of prey
for chimps is the colobus monkey.

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124 USING ANIMAL MODELS TO UNDERSTAND HUMAN BEHAVIOR

Conservation of chimpanzees

Orphaned chimps—their mothers According to the Jane Goodall chimp communities when roads
killed for bushmeat—walk along a Institute in Tanzania, the number are built through their territories.
mud track with their keeper at a of chimpanzees living in the wild Roads also encourage another
conservation center in West Africa. has plummeted over the last damaging activity—hunting
century. In 1900, there were an for bushmeat, a highly valued
estimated 1 million chimpanzees meat in Africa that includes
in Africa; today, there are fewer great apes. Roads enable
than 300,000. Habitat loss due to hunters from towns to travel
a rising human population in need directly into the bush. The
of more space has had a huge protection of chimps focuses
impact, as have industries such on land conservation and on
as logging and mining, which raising awareness both locally
destroy habitat and fragment and across the globe.

Such behavior has implications Although chimps sometimes hunt for the war was unclear; some
for human evolution. Science has alone, hunting tends to be a group researchers blamed the feeding
long questioned why and when activity. Chimps rampage through stations Goodall had set up in the
humans first began eating meat. the forest, coordinating their area, which may have encouraged
From prehistoric stone tools and positions and surrounding their unnatural congregations of chimps.
marks on bones, paleontologists prey. After the hunt, the food is The answer to the mystery came
know that the early hominids shared. This shows how early in March 2018, when a research
were using stone tools to cut meat ancestors of humans may have team at Duke and Arizona State
from animals bones 2.5 million developed cooperative behavior, Universities, US, digitized Goodall’s
years ago, but it is not known a factor that may have contributed meticulous check sheets and field
what they were eating between to their evolutionary success. notes from 1967 to 1972 and fed
then and 7 million years ago, them into a computer in order to
when the common ancestor Chimp warfare analyze the social networks and
of chimpanzees and humans A shocking revelation that came alliances of all the male chimps.
is thought to have lived. out of the Gombe camp was that Their findings revealed that the
chimps are capable of violence, fracture in the community occurred
It is likely that these early murder, and in particular warfare— two years before the war broke
hominids hunted prey. Although once believed to be the preserve out, when an alpha male Goodall
they did not have large canine of humans. Between 1974 and 1978, called Humphrey took over the
teeth like chimpanzees, these are Jane Goodall watched as her troupe, alienating two other high-
not necessary for hunting and peaceful community of chimps
killing small prey. Biologists have fractured into two rival groups that
observed that chimps hunting then waged savage war on each
colobus monkeys grab them from other. Goodall was deeply upset
the trees and then kill them by about the chimps’ activity, which
repeatedly thumping the bodies included ambushes, kidnappings,
on the ground; early hominids and bloody murder. The trigger
could have hunted and killed
in a similar fashion long before Chimps may fight over territory
the earliest known tools. in order to acquire more resources
or mates, but some primatologists
Cooperative behavior maintains that such aggression is
Another aspect of chimps’ hunting unnatural and provoked by human
behavior that is similar to that impact on their habitat.
of humans is the social element.

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THE VARIETY OF LIFE 125

I’m determined my associated with food resources and piece of fruit hanging over one room
great grandchildren meat eating. When food is limited, (B). The bonobo in room A could
the chimps become more violent release the fruit but not get to it
will be able to in order to obtain the resources himself. The researchers found that
go to Africa and they need. Chimps are known to this bonobo would consistently
find wild great apes. eat more meat when fruit is scarce. release the fruit, so that the other
Jane Goodall one could reach it, helping a
Kissing cousins stranger, with no reward for himself.
ranking males called Charlie and The link between food scarcity
Hugh and causing them to split and aggression in the common Researchers also observed how
off with some other chimps to the chimpanzee may explain why our the sight of an unknown bonobo
south. The two groups became other evolutionary cousin in the yawning in a film would trigger
more and more separate, feeding primate world, the bonobo (pygmy a yawning response in bonobos
in different parts of the forest. At chimp), is so peace-loving. These watching the film, suggesting a
first there was the odd aggressive small, placid chimps are omnivores capacity for empathy. Other studies
skirmish and then war broke out. but live in an environment where have shown how bonobos comfort
Over four years, Humphrey and his fruit is plentiful most of the time. each other when in distress. Unlike
cohorts killed every male in the They forage in groups, and tend the “negative” behavior that
southern group and took over their to use sex to relieve tensions in humans share with chimps,
territory, as well as three surviving social situations. Conflict is rare these traits mirror more laudable
females. It is thought that the full- in bonobo societies, which are human characteristics, such as
blown war may have been due also matriarchal, unlike the male- compassion. Understanding such
to a lack of mature females in the dominated chimp communities. behavior in bonobos could shed
northern group. Power struggles light on how our human social
and fighting over a female all sound An experiment carried out by behavior developed. ■
very human. researchers at Duke University,
North Carolina, in 2017 showed Bonobos are very social primates.
that bonobos are also altruistic. Two Their capacity for empathy makes
bonobos (unknown to each other) them less aggressive and may align
were put in adjacent rooms (A and B) them more closely with their human
with a fence between them and a cousins than the common chimpanzee.

Fights over resources
The long-running war witnessed
by Goodall is the only sustained
conflict among chimpanzees to
have been fully documented,
but violence within chimp
communities has been recorded
many times. Chimps have been
observed stealing and killing baby
chimps and rounding on a disliked
alpha male. In communities studied
in Uganda, males routinely beat
the females they mate with. It is
thought that this violent streak
running through chimps may be

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126

DTAEELMPLEPBNEODRDSAILTOYUNRAECTIVITY

THERMOREGULATION IN INSECTS

IN CONTEXT Insects are usually described as known that many insects are
“cold-blooded,” or ectotherms. heterotherms, maintaining different
KEY FIGURE Unlike mammals and other temperatures in different parts of the
Bernd Heinrich (1940–) “warm-blooded” endotherms, body, and are sometimes far warmer
animals that maintain their body than the ambient temperature.
BEFORE temperature at a more or less
1837 In the UK, George constant level, insects have a The right temperature
Newport observes that flying variable body temperature that The main challenge facing insects
insects are capable of raising changes with their environment. is how to get warm enough to fly
their body temperature above but cool enough not to overheat.
the ambient temperature. In the early 19th century, German–American entomologist
however, British entomologist Bernd Heinrich explained in 1974
1941 Danish researchers George Newport discovered that how moths, bees, and beetles could
August Krogh and Eric some moths and bees raise the continue to function by controlling
Zeuthen conclude that the temperature of their thorax (the their own temperature. He realized
temperature of an insect’s central part of the body, to which that insects’ thermal adaptations
flight muscles just before wings and limbs attach) above that do not differ as much from those of
takeoff determine the muscles’ of the surrounding air by rapidly vertebrates as had been thought.
rate of work during flight. flexing their muscles. It is now
Most flying insects have higher
AFTER In insects… the active metabolic rates than other animals
1991 German biologist Harald flight muscles… are, but their small body size means they
Esch describes how muscle metabolically, the most lose heat rapidly, so they cannot keep
“warm-up” plays a role in brood active tissues known. their temperature constant at all
incubation and colony defense times. The minimum temperature
as well as flight preparation. Bernd Heinrich that allows an insect to fly varies
from species to species, but the
2012 Using infrared maximum temperature falls within
thermography, Spanish 104–113°F (40–45°C). To prevent
zoologist Jose R. Verdu shows overheating, insects can transfer
how some dung beetle species heat from the thorax to the abdomen.
heat or cool their thorax to
improve flight performance. Many larger flying insects would
remain grounded if they were not
able to increase the temperature of
their flight muscles. These insects

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THE VARIETY OF LIFE 127

See also: Evolution by natural selection 24–31 ■ Ecophysiology 72–73 Heat regulation
■ Animal ecology 106–113 ■ Organisms and their environment 166
Honeybees are renowned for
“quiver” the muscles that control A tortoiseshell butterfly feeds on controlling the temperature
the upbeat and downbeat of the a dandelion. Most butterflies can angle of their hive. When it gets too
wings to generate heat before their wings upward in an attempt hot, they ventilate it by using
taking off. Once flying, the muscles to cool down, in a process called their wings to fan the hot air
use large amounts of chemical behavioral thermoregulation. out of the nest. When it gets
energy but only some of it is used too cold, the bees generate
to beat the wings; the rest becomes Other insects use even more metabolic heat by rapidly
more heat. This, combined with the remarkable methods to regulate their contracting and relaxing their
warmth of direct sunlight, means body temperature. When a mosquito flight muscles. They also use
a flying insect risks overheating. drinks the warm blood of a mammal, heat as a defense mechanism.
this raises its body temperature. To Japanese giant hornets are
To solve this problem, many compensate, it produces droplets of fierce predators of honeybees.
species have a heat-exchange fluid that are kept at the end of the Capable of killing large
mechanism that shifts excess heat abdomen; evaporative cooling of numbers quickly, they pose a
from the thorax to the abdomen, these droplets lowers the insect’s serious threat to bees’ nests.
allowing the insect to maintain temperature. Dung beetles construct Hornets begin their attacks by
a steady temperature in its thorax. balls of dung in which females lay picking off single honeybees
their eggs. Some dung beetles are at the entrance to the hive.
Range of techniques able to raise the temperature of their However, Japanese honeybees
By changing the angle of their thorax so they can roll heavier balls. defend themselves with
wings, butterflies control their body self-generated heat. If a hornet
temperature. When they are trying The range of thermoregulation attacks, they swarm around it,
to warm up, holding their wings techniques shows how life forms vibrating their wings to raise
wide open maximizes the amount evolve to better fit their environment. their collective temperature.
of sunshine falling on them. When They can also inspire technology: Since the hornet cannot
they are trying to cool down, they arrays of solar panels angled to tolerate a temperature above
move into shade or angle their track the Sun capture maximum 114.8°F (46°C) whereas the
wings upward so that less direct amounts of solar radiation—just like bees can survive at almost
sunlight shines on their surface. butterfly wings. ■ 118.4°F (48°C), the attacker
eventually dies.

This Japanese giant hornet is
raiding nursery cells in a bees’
nest in Hase Valley, Japan. Hornets
seek to devour the bee larvae
inside the cells.

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ECOSYST

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EMS

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130 INTRODUCTION

Richard Bradley Charles Elton The journal Ecology Nelson Hairston,
describes how plants, develops the idea of posthumously publishes Frederick Smith, and
the food web in Animal Raymond Lindeman’s article Lawrence Slobodkin’s
pollinating insects, Ecology and introduces “The trophic-dynamic “green world hypothesis”
and insectivores rely the concept of the argues that the predator–
on one another in a ecological niche. aspect of ecology.” prey balance is key to
flourishing ecosystems.
food chain.

1718 1927 1942 1960
1859 1935 1957

Charles Darwin Arthur G. Tansley coins the G. Evelyn Hutchinson
describes food term ecosystem, arguing establishes the concept
webs in his On the that an environment and all
Origin of Species. its living organisms have of niche breadth at
the Cold Spring
to be seen as a single,
interactive whole. Harbor Symposia on
Quantitative Biology.

W hen Aristotle wrote The concept of the ecosystem (“a They identified both the top-down
about plant and animal recognizable self-contained entity”) pressures exerted by predators and
species existing for the followed soon after, when in 1935, the bottom-up pressures exerted by
sake of others, he showed a basic British botanist Arthur Tansley limitations on food supply. Twenty
understanding of food chains— wrote that organisms and their years later, American ecologist
as have countless observers of the environment should be considered Robert Paine wrote of the trophic
natural world since ancient Greek one physical system. In his Ph.D. cascade effect—the way a system
times. Arab scholar Al-Jahiz thesis, American ecologist is changed by the removal of a key
described a three-level food chain Raymond Lindeman expanded species. He described changes to
in the 9th century, as did the on Tansley’s work, positing that the food web after the experimental
Dutch microscopist Antonie van ecosystems are composed of removal of the ocher starfish from
Leeuwenhoek in 1717. British physical, chemical, and biological an intertidal zone. This predatory
naturalist Richard Bradley processes “active within a space– echinoderm was shown to be a
published more detailed findings time unit of any magnitude.” keystone species, playing a crucial
on food chains in 1718, and in 1859, role within its ecosystem.
Charles Darwin described a “web Lindeman also conceived the
of complex relations” in the natural idea of feeding levels, or trophic Island isolation
environment in his book On the levels, each of which is dependent Habitat fragmentation is now a
Origin of Species. The concept of a on the preceding one for its survival. major problem in most terrestrial
food web, with many predator-prey In 1960, the American team of environments because it leaves
interactions, was then further Nelson Hairston, Frederick Smith, specialist organisms isolated.
developed by Charles Elton in his and Lawrence Slobodkin published For that reason, research into the
classic Animal Ecology (1927). findings on the factors controlling biogeography of islands—those
animals on different trophic levels.

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ECOSYSTEMS 131

John Maynard Smith Hal Caswell proposes Scientists at the
defines his a “neutral” theory Biodiversity and
Ecosystem Function
Evolutionarily Stable of biodiversity, suggesting conference in Paris
Strategy (ESS) theory that competitors are often examine how the
equal, and chance plays
in On Evolution. loss of species
the deciding role in impacts ecosystems.
what does or doesn’t thrive.

1972 1976 2000
1967 1973 1980 2015

Robert MacArthur Crawford Stanley Robert Paine coins the term A study of grassland plants
examines the Holling uses the “trophic cascade” after his suggests that biodiversity
term ecological field experiments show the increases an ecosystem’s
biodiversity of resilience to show how
isolated communities ecological systems effect on an ecosystem resistance during
survive change. when a keystone species and resilience after
in The Theory of
Island Biogeography. is removed. climate events.

surrounded by ocean but also evolutionarily stable strategy (ESS) after a trauma. Ecologists now
“islands” of distinct habitat to describe the best behavioral understand that ecosystems can
surrounded by a very different strategy for an animal competing have more than one stable state,
environment—is so important with others living in its vicinity. and that resilient systems are not
in ecology. In the US in the 1960s, This strategy depends on how the always good for biodiversity.
Edward O. Wilson and Robert other animals behave and is
MacArthur discovered key factors determined by the animal’s genetic When the populations of many
determining species diversity, success—if it makes the wrong species are declining or becoming
immigration, and extinction on decisions, it will not live long and locally extinct, ecologists are once
islands. James Brown later did cannot pass on its genes. The more focusing their attention on
similar work on animal populations overall balance between the ecosystem resilience. Many,
in isolated patches of forest ridge in evolutionarily stable strategies of including French ecologist Michel
California. Such work has showed all the animals in an ecosystem is Loreau, believe that if diversity in
how to identify species most at risk called the evolutionarily stable state. an ecosystem is reduced, the whole
of extinction due to isolation. system will be less likely to resist
Canadian ecologist Crawford major impacts such as the effects of
Stability and resilience Stanley Holling introduced the idea climate change. Today, Loreau and
One major contribution to the of resilience—how ecosystems others are working toward finding a
understanding of ecosystem persist in the wake of disruptive new general theory that can
dynamics was the concept of the changes such as fire, flood, or explain the relationship between
evolutionarily stable state. In the deforestation. A system’s resilience ecosystem biodiversity and
1970s, British biologist John can be seen in its capacity to absorb resilience in order to understand
Maynard Smith used the term disturbance, or the time it takes to and combat the effects of today’s
return to a state of equilibrium environmental challenges. ■

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132

IESOSVUFENPNRPEAYCOTERDUSTIRSSEOTA’FISRNTYWCHFTOEOPRRRAKERTSSTHTE

THE FOOD CHAIN

IN CONTEXT The food chain A ll animals must eat other
living things in order to
KEY FIGURE Apex predator receive the nutrients they
Richard Bradley (1688–1732) Larger predator need to grow and function. A food
(tertiary consumer) chain shows the feeding hierarchy
BEFORE of different animals in a habitat.
9th century Arab scholar Carnivore For example, the chain would show
Al-Jahiz describes a three- (secondary consumer) that foxes eat rabbits but rabbits
level food chain of plant matter, never eat foxes. Although there
rats, snakes, and birds. Herbivore were earlier notions of a hierarchy
(primary consumer) of animals linked to each other in
1717 Dutch scientist Antonie a food chain, British naturalist
van Leeuwenhoek observes Producer (autotroph) Richard Bradley brought more
how haddock eat shrimp and detail to this idea in his book New
cod eat haddock. Improvements in Planting and
Gardening (1718). He noted that
AFTER each plant had its own particular
1749 Swedish taxonomist Carl set of insects that lived off it and
Linnaeus introduces the idea proposed that the insects in turn
of competition. received the attentions of other
organisms of “lesser rank” that fed
1768 John Bruckner, a Dutch on them. In this way, he believed
naturalist, introduces the idea that all animals relied upon each
of food webs. other in a self-perpetuating chain.

1859 Charles Darwin writes Producers and consumers
about food webs in On the The modern concept of a food chain
Origin of Species. explains that some organisms
produce their own food. These are
1927 British zoologist Charles known as producers, or autotrophs.
Elton’s Animal Ecology outlines Plants and most algae fall into this
principles of animal behavior, category, normally using the energy
including food chains. of sunlight to convert water and
carbon dioxide into glucose, at the

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ECOSYSTEMS 133

See also: Predator–prey equations 44–49 ■ Mutualisms 56–59 ■ Keystone species 60–65 ■ Optimal foraging theory 66–67
■ Animal ecology 106–113 ■ The ecosystem 134–137 ■ Trophic cascades 140–143 ■ Ecological resilience 150–151

Each species has a
specific place in nature,
in geographic location
and in the food chain.

Carl Linnaeus

same time as releasing oxygen. of the food chain, but there is always An apex predator, such as the bronze
This process, photosynthesis, is the a producer at the bottom, and all whaler shark, has no natural predators.
first step towards creating food. In levels above it are consumers. In the temperate waters of the ocean
places where there is no sunlight, Animals that only eat plants are off South Africa the shark can find vast
organisms producing their own herbivores, or primary consumers, quantities of sardines to eat.
food are called chemotrophs. Those and they include cattle, rabbits,
in the deep ocean, for example, get butterflies, and elephants. Those of prey. The animals at the top of
the energy they need from chemicals that eat only other animals are their food chain are apex predators.
released by hydrothermal vents. carnivores, or secondary consumers; They include consumers such as
these include thrushes, dragonflies, tigers, killer whales, and golden
Animals that eat producers and and hedgehogs. In turn, secondary eagles that are not preyed upon
creatures that eat other animals are consumers may be eaten by larger by other animals.
called consumers, or heterotrophs. predators, or tertiary consumers,
There may be two, three, or more such as foxes, small cats, and birds The food chain does not break
levels of these in any particular part when plants and animals die.
infections were caused by tiny Detritus feeders (detritivores) prey
Richard Bradley organisms, visible only with a on the remains, recycling nutrients
microscope. His investigations and energy for the next generation
Born around 1688, noted British into the productivity of rabbit of producers to use.
botanist Richard Bradley gained warrens and fish lakes led to
patrons after writing a Treatise his theories about predator–prey Food webs
of Succulent Plants at the age of relations. Bradley died in 1732. Observers after Bradley suggested
22. With no university education, that animals were not simply part
he was nonetheless elected a Key works of a food chain, but a larger and
Fellow of the Royal Society and more complex “food web” that
later became the first professor 1716–27 The History of comprises all the food chains in a
of botany at Cambridge. Succulent Plants location. This idea was put forward
1718 New Improvements in by Dutch naturalist John Bruckner
Bradley’s research interests Planting and Gardening in 1768, and later taken up by
were wide-ranging, including 1721 A Philosophical Account of Charles Darwin, who called the
fungal spore germination and the Works of Nature variety of connected feeding
plant pollination. In some cases, relationships between species
Bradley was ahead of his time; a “web of complex relations”. ■
he argued, for example, that

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134

FOSAAOLRROOLGEUDRAOPNCROFIEGOTSSERAMNNOOSTIFSTIAHMLESR IN CONTEXT

THE ECOSYSTEM KEY FIGURE
Arthur Tansley
(1871–1955)

BEFORE
1864 George Perkins Marsh,
an American conservationist,
publishes Man and Nature,
which hints at the concept
of ecosystems.

1875 Austrian geologist
Eduard Suess proposes
the term “biosphere.”

AFTER
1953 American ecologists
Howard and Eugene Odum
develop a “systems approach”
to studying the flow of energy
through ecosystems.

1956 American ecologist
Paul Sears highlights
the role of ecosystems
in recycling nutrients.

1970 Paul Ehrlich and Rosa
Weigert warn of potentially
destructive human
interference in ecosystems.

B ritish biologist Arthur
Tansley was the first to
insist that communities
of organisms in a particular area
had to be seen in a wider context,
including the nonliving elements
of that area. Tansley argued that
in a given region, all the living
organisms and their geophysical
environment together form a single,
interactive entity. Borrowing a
concept from engineering, he saw
the network of interactions as a
dynamic, physical system. On the
suggestion of his colleague Arthur
Clapham, he coined the word
“ecosystem” to describe it.

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ECOSYSTEMS 135

See also: Animal ecology 106–113 ■ The food chain 132–133 ■ Energy flow through ecosystems 138–139 ■ The biosphere
204–205 ■ The Gaia hypothesis 214–217 ■ Environmental feedback loops 224–225 ■ Ecosystem services 328–329

Tropical coral reefs are some of the
most diverse ecosystems of all, full of
fish, sea turtles, crustaceans, mollusks,
and sponges, as well as corals.

This idea had been developing
long before Arthur Tansley
published his influential paper
on the subject in 1935. As early
as 1864, conservationist George
Perkins Marsh, in his book Man
and Nature, had identified “the
woods,” “the waters,” and “the
sands” as different types of habitat.
He examined how the relationship
between them and the animals and
plants that lived in them could be
upset by human activity.

Interconnected systems a single unit, and using the term nitrogen, and soil minerals, which
By the 20th century, the idea had “biome” to describe the whole are essential to the functioning of
taken hold that these and other complex of organisms inhabiting the systems as a whole. The biotic
environments could be understood a given region. components within an ecosystem
as discrete entities, with distinctive not only interact with one another,
interactions between the living Tansley envisaged ecosystems but also with the abiotic parts.
and inert elements within them. In as being made up of biotic (living) Thus, within any given ecosystem,
1916, American ecologist Frederic elements and abiotic (nonliving) the organisms adapt to both the ❯❯
Clements built on this idea in his elements such as energy, water,
work on plant succession, referring
to a “community” of vegetation as

Arthur G. Tansley A free-thinking Fabian socialist He retired in 1937, but
and atheist, Arthur Tansley was maintained a special interest
one of the most influential in conservation. Tansley was
ecologists of the 20th century. appointed the first Chairman of
Born in London in 1871, he studied the UK’s Nature Conservancy in
biology at University College 1950, five years before his death.
London, where he later taught.
In 1902, he founded the journal Key works
New Phytologist and he later
established the British Ecological 1922 Types of British Vegetation
Society, becoming founding editor 1922 Elements of Plant Ecology
of its Journal of Ecology. In 1923, 1923 Practical Plant Ecology
he took a break from teaching to 1935 “The use and abuse of
study psychology with Sigmund vegetational terms and
Freud in Vienna. He was later concepts,” Ecology
Sherardian Professor of Botany 1939 The British Islands and
at the University of Oxford. Their Vegetation

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136 THE ECOSYSTEM

biological and physical elements matter: plants absorb carbon A small glacial lake, or tarn, in the
of the environment. The different dioxide (CO2) from the atmosphere English Lake District. Each tarn has
types of ecosystem can be defined and nutrients from the soil to grow. an ecosystem that varies according
by their physical environments. These plants release life-sustaining to many factors, including the degree
There are four categories of oxygen into the atmosphere by of nutrient enrichment in the water.
ecosystem: terrestrial, freshwater, respiration, and provide food for
marine, and atmospheric. These animals. Animal excreta and dead Each ecosystem is located in a
can be further subdivided into matter also release carbon, and particular area, with characteristics
various types according to different provide material to be decomposed unique to its environment, and
physical environments and the by bacteria and fungi, in turn behaves as a self-contained and
biodiversity within them. Terrestrial providing soil nutrients for plants. self-regulating system. Together,
ecosystems, for example, can be the patchwork of ecosystems
subdivided into deserts, forests, Arthur Tansley also argued across the globe form what
grasslands, taigas, and tundras. that these internal processes Austrian scientist Eduard Suess
within an ecosystem conform to called the biosphere—the sum
Dynamic feedback what he described as “the great total of all ecosystems.
Tansley’s most important insight universal law of equilibrium.”
was that these discrete communities Self-regulating, these processes External factors
of living and nonliving components have a natural tendency toward Various external factors, such as
form dynamic systems. In a stability. The cycles within an climate and the geological makeup
terrestrial ecosystem, for example, ecosystem contain feedback loops of the surrounding environment,
the organisms interact to recycle that correct any fluctuations from can affect an ecosystem. One
a state of equilibrium. constant external force that affects
all ecosystems is the Sun. The
The dynamic transfer of energy supply of energy that it provides
enables photosynthesis and the
In this ecosystem, plants use the Sun’s energy capture of CO2 from the atmosphere;
for photosynthesis. As shown by the pale arrows, some of this energy is distributed
this energy is passed on—to herbivores, who eat through the ecosystem and through
plants; to predators, who eat herbivores; and to the food chain. In the process, some
saphrophytes, who take energy from decomposing of this energy dissipates as heat.
remains and transfer nutrients to the soil.
At each stage, some energy is lost as heat. Other external factors, however,
can arise unexpectedly to create
Heat pressures on ecosystems. All
ecosystems are subjected to
Heat external disturbances from time
to time, and must then go through
Plants Heat a process of recovery. These
(producers) disturbances include storms,

Frog
(predator)

Saphrophytes Fish Nutrients
and parasites (herbivores)
(decomposers)

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ECOSYSTEMS 137

There is no waste in more fragile, and if they are wholesale destruction of habitat
functioning … ecosystems. disturbed may never be able and the consequent depletion of its
All organisms, dead or alive, to regain their equilibrium. biodiversity. In addition, some have
are potential sources of food suggested that human influence
The resistance and resilience has created a new category
for other organisms. of an ecosystem is generally of ecological systems, dubbed
G. Tyler Miller thought to be related to its “techno-ecosystems.” For example,
biodiversity. If, for example, “cooling ponds” are manmade
Science writer there is only one species of plant ponds, built to cool down nuclear
performing a particular function power plants, but they have become
earthquakes, floods, droughts, and in the system, and that species is ecosystems for aquatic organisms.
other natural phenomena, but are not frost-resistant, an abnormally
increasingly the result of human severe winter could deplete the The relationship between
activity—through the destruction species enough to have a major humans and natural ecosystems
of natural habitats by deforestation, impact on the system as a whole. is not all negative. In recent years,
urbanization, pollution, and the In contrast, if there are several scientific data has fueled public
cumulative effects of anthropogenic species with that role in the awareness of the benefits that
(human-induced) climate change. system, it is more likely that one ecosystems afford humankind,
Humans can also be responsible will be resistant to the disturbance. including the provision of food,
for the introduction of invasive water, nutrients, and clean air,
species. Without these external The human factor as well as the management of
factors, an ecosystem would Some disturbances can be severe disease and even climate. There
maintain its state of equilibrium, enough to be catastrophic for an is now a growing commitment from
and retain a stable identity. ecosystem, damaging it beyond many governments across the
the point of recovery and so world to use these benefits both
causing a permanent change responsibly and sustainably. ■
in its identity, or even its demise.
The fear is that much of the The Eden Project, in Cornwall, UK,
disturbance caused by human simulates a rain forest ecosystem in
activity has the potential to one of its giant dome greenhouses. The
cause such permanent damage, domes’ panels are slanted to absorb
particularly when it involves the plenty of light and thermal energy.

Resistance and resilience
Ecosystems are often strong
enough to withstand some natural
external disturbances and retain
their equilibrium. Some are more
resistant to disturbance than
others, and have adapted to the
particular disturbances normally
associated with their environment.
In some forest ecosystems, for
example, the periodic fires caused
by electrical storms cause only a
minor imbalance in the ecosystem.

Even when severely disrupted
by external disturbances, some
ecosystems have a resilience
that enables them to recover.
However, other ecosystems are

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138

OBLIYFFAPERVISOACSSETUSPNSPEEOTSRWTOERDK

ENERGY FLOW THROUGH ECOSYSTEMS

IN CONTEXT I n 1941, Raymond Lindeman his Ph.D., but his paper was initially
submitted the final chapter of rejected by Ecology, for being
KEY FIGURE his Ph.D. thesis for publication too theoretical.
Raymond Lindeman in the prestigious journal Ecology.
(1915–42) Titled “The Trophic-dynamic Lindeman had painstakingly
Aspect of Ecology,” it was about sampled everything in the lake,
BEFORE the relationship between food from the aquatic plants and
1913 American zoologist chains and the changes over time microscopic algal plankton to the
Victor Shelford produces the in a community of species. worms, insects, crustaceans, and
first illustrated food webs. fish that fed upon one another and
Lindeman had spent five years depended on each other for their
1920 Frederic Clements studying the life forms in an aging existence. He stressed that the
describes how groups of plant lake at Cedar Creek Bog, Minnesota, community of organisms could not
species are associated in and was especially interested in be properly understood on its own;
communities. the changes in the lake as, year instead, it must be examined in the
by year, aquatic habitat gradually context of its wider surroundings.
1926 Russian geochemist gave way to land. He received The living (biotic) organisms and
Vladimir Vernadsky sees that
chemicals are recycled between Producers (plants and Primary consumers
living and nonliving things. algae) depend on energy are dependent on an
gathered from the Sun and abundance of plants
1935 Arthur Tansley develops nutrients from decomposed
the concept of the ecosystem. and algae to eat.
organic matter.
AFTER
1957 American ecologist Life is supported Secondary consumers
Eugene Odum uses radioactive by a vast network rely on an abundance of
elements to map food chains. primary consumers as
of processes.
1962 Rachel Carson draws their food source.
attention to the accumulation
of pesticides in food chains,
in her book Silent Spring.

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ECOSYSTEMS 139

See also: Ecological niches 50–51 ■ Nonconsumptive effects of predators Measuring
on their prey 76–77 ■ The food chain 132–133 ■ The ecosystem 134–137 productivity

Boneworms are deep-sea creatures Lindeman’s trophic-dynamic
that feed on the remains of animals theory helped to clarify the
such as whales. They grow “roots” to idea of ecosystem productivity,
break down the bones, thereby recycling which ecologists had previously
nutrients from the dead material. defined in rather vague terms.
The productivity of a plant
the nonliving (abiotic) components Lindeman also demonstrated how or animal is measured by its
(air, water, soil minerals) were some of the energy at each trophic growth in organic material,
linked together by nutrient cycles level is lost as waste, or converted or biomass. This is never equal
and energy flows. This entire into heat when organisms respire. to the organism’s energy
system—the ecosystem—was By combining the results of his own input, because the conversion
the central ecological unit. study with data from a wide range of solar energy into leaf in the
of other sources, he was able to case of plants, or the conversion
Producers and consumers build a picture of this system as it of food into flesh in the case of
Lindeman’s research showed how worked in Cedar Creek Bog. an animal, is never 100 percent
an ecosystem is powered by a efficient. Some energy is
stream of energy from one organism British ecologist G. Evelyn released as heat, most of which
to another. The organisms can be Hutchinson, considered to be one is lost via respiration—an
grouped into discrete “trophic levels” of the founding fathers of modern essential aspect of metabolism
(feeding levels)—from producers ecology, was Lindeman’s mentor at in all living things.
(plants and algae), which absorb Yale University. He recognized the
energy in the form of sunlight to importance of his student’s work to Warm-blooded animals lose
make food, to consumers (animals). the future development of ecology, a lot of heat when their body
“Primary consumers” are the and he lobbied for Lindeman’s temperature is much higher
herbivores that eat the plants; paper to be accepted. Lindeman, than that of their surroundings.
“secondary consumers” are animals who had always suffered from ill All animals also lose energy
that eat the herbivores. Each trophic health, died in 1942 from cirrhosis when they excrete urine. In
level depends on the preceding one of the liver at the tragically young addition, not all the material
for its survival. At the same time, age of 27, just four months before in an animal’s food can be
dead material accumulating from his trophic-dynamic paper—now digested in its gut, and the
each stage is broken down by seen as a classic in its field—was material that is expelled as
decomposers, such as bacteria and finally published. ■ feces represents unused
fungi, and materials in the form of chemical energy.
nutrients are recycled back to feed … biological communities
plants and algae. could be expressed as This thermal image of an
elephant shows how some of the
networks or channels through animal’s heat is lost. Both its body
which energy is flowing and temperature and its manure are
warmer than the surroundings.
being dissipated…
G. Evelyn Hutchinson

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140

ITSHGERWEOENRLD IN CONTEXT

TROPHIC CASCADES KEY FIGURE
Nelson Hairston (1917–2008)

BEFORE
1949 Aldo Leopold publishes
A Sand County Almanac,
drawing attention to the
ecological impact of hunting
wolves on mountain plant life.

AFTER
1961 Lawrence Slobodkin,
an American marine
ecologist, publishes The
Growth and Regulation of
Animal Populations, a key
ecology textbook.

1980 Robert Paine describes
the “trophic cascade effect,”
when predators are removed
from an intertidal ecosystem.

1995 The reintroduction of
gray wolves to Yellowstone
National Park sets in motion
a series of ecosystem changes.

S oon after the end of World
War II, Aldo Leopold, an
ecologist and one of the top
wildlife management experts in the
United States, challenged the view
that wolves should be eradicated
because they threatened livestock.
In A Sand County Almanac, he
wrote of the destructive effect that
removing this top predator would
have on the rest of the ecosystem.
In particular, he said, it would lead
to overgrazing of mountainsides by
deer. Leopold’s view was an early
expression of the idea of trophic
cascades, although he himself did
not use that term.

Predators help keep a balance
in a food web by regulating the
populations of other animals. When

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ECOSYSTEMS 141

See also: Predator–prey equations 44–49 ■ The food chain 132–133 ■ The ecosystem 134–137 ■ Energy flow through
ecosystems 138–139 ■ Evolutionarily stable state 154–155 ■ Biodiversity and ecosystem function 156–157

Ocher starfish prey on sea creatures different trophic levels. They he described changes in food
such as mussels and limpets. In a concluded that populations of webs that were brought about
famous experiment, Robert Paine took producers, carnivores, and by the experimental removal
them out of their rock pools to observe decomposers are limited by their of predatory starfish from the
the effect on the rest of the food web. respective resources. Competition intertidal zone in Washington
occurs between species on each of State. The concept of trophic
they attack and eat prey, they affect these three trophic levels. They also cascades is now generally accepted,
the number and behavior of that found that herbivore populations although debate continues as to
prey—since prey move away when are seldom limited by the supply of how widespread they are.
predators are present. The impact plants, but are limited by predators,
of a predator can extend down to the so they are unlikely to compete Top-down cascades
next feeding level (trophic level), with other herbivores for common This type of cascade is clearly
affecting the population of the prey’s resources. The paper highlighted demonstrated when a food chain
own food source. In essence, by the important role of top-down is interrupted by the removal of
controlling the population density forces (predation) in ecosystems, a top predator. The ecosystem
and behavior of their prey, predators and bottom-up forces (food supply). may continue to function despite
indirectly benefit and increase the the shift in species composition;
abundance of their prey’s prey. American ecologist Robert alternatively, the removal of one
Paine was the first to use the term species may lead to the ❯❯
Indirect interaction that occurs “trophic cascade” when, in 1980,
across feeding levels is described
by ecologists as a trophic cascade. Predators eat
By definition, trophic cascades must herbivore prey
cross at least three feeding levels.
Four- and five-level trophic cascades Bottom-up cascade Top-down cascade
are also known, although these are
less common. Predators move into the If predators are
area and numbers increase removed …

Herbivore population Prey population increases
increases

Controlling factors Increased rainfall Overgrazing brings
In 1960, the American ecologist encourages vegetation habitat change and loss
Nelson Hairston and his colleagues
Frederick Smith and Lawrence of species richness
Slobodkin published a key paper
entitled “Community Structure, Herbivore prey eat plants
Population Control, and Competition,”
which examined the factors that
control populations of animals on

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142 TROPHIC CASCADES

ecosystem’s breakdown. In the US, benthic invertebrate species. This Just as a deer herd lives
a trophic cascade on the coast of in turn led to an increase in floating in mortal fear of its wolves,
southern New England is believed nutrients, which ultimately boosted
to be responsible for the die-off of phytoplankton rather than species so does a mountain live
saltmarsh habitat. Recreational on the sea floor. The net effect of in mortal fear of its deer.
anglers have reduced the number the crabs’ arrival was to transfer
of predatory fish to such an extent nutrients from the sea floor to the Aldo Leopold
that the number of herbivorous water column—the water between
crabs has expanded dramatically. the sediment and the surface—and plants support more herbivores and
The resulting increase in the to degrade the ecosystem. more predators. This is in contrast to
consumption of marsh vegetation top-down cascades, in which more
has had a knock-on effect on other Bottom-up cascades predators lead to fewer herbivorous
species that depend on it. If a plant—a primary producer— prey and a greater mix of plants.
is removed from an ecosystem, a
Trophic cascades can also be bottom-up cascade may result. For Beetles, ants, and moths
disturbed by the introduction and example, if a fungal disease causes Investigating trophic cascades
spread of a nonnative species, as grass to die-off, a rabbit population in four-tier systems is more difficult,
happened when the omnivorous that depends on it will crash. In because predators at the top
mud crab indigenous to waters turn, the predators that eat rabbits feeding level may eat predators at
on the east coast of North America will starve or be forced to move the level below and also herbivores
and Mexico became common in away, and the entire ecosystem below them, so the relationships
the Baltic Sea in the 1990s. Crabs, could break down. Conversely, become very complex. In 1999,
which are keystone species in if planting or conservation efforts researchers studying trophic
many coastal food webs, feed on boost the mix of plant life, more cascades in tropical rain forest in
benthic (seafloor) communities— herbivores (including the pollinators Costa Rica got around this problem
bivalves, gastropods, and other that help plants reproduce and by studying a system of three
small invertebrates—with spread) will be attracted, and with trophic levels of invertebrates, in
devastating efficiency, creating them more predators. which the top predator—a clerid
a strong top-down cascade. The beetle—ate the predatory ants
increase in the number of mud In the bottom-up model, the in the level below it, but not the
crabs in the Baltic, where there are responses of herbivores and their herbivores in the level below that.
no equivalent predators, resulted predators to increased plant variety When the number of predatory
in a dramatic decline in the mix of follow in the same direction: more beetles in the study area was
increased, the population of
predatory ants fell dramatically.
This reduced the pressure on
dozens of species of herbivorous

Californian yellow bush lupines
are fast growing and invasive. The
plant can upset the ecosystem by
causing elevated nitrogen levels that
attract nonnative species.

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ECOSYSTEMS 143

Early humans
and megafauna

Steller’s sea cow was a giant cascade, triggered by the hunting In the last 60,000 years, which
sirenian discovered by the naturalist to virtual extinction of sea otters for includes the end of the last ice
Georg Steller in 1741. Its extinction is the fur trade. The over-exploitation of age, about 51 genera of large
the cause of debate: was it hunted to sea otters allowed the population mammals became extinct in
death, or did its food source disappear? of sea urchins, their usual prey, to North America. Most were
rise above a critical threshold. Sea herbivores, including ground
invertebrates, which therefore ate urchins eat kelp, so the growth of sloths, mastodons, and large
more vegetation. The leaf area their population led to a collapse in armadillos, but many were
of the plants in the study was the extent of kelp forests—the sea carnivores, such as American
consequently reduced by half. cows’ food source. Although the lions and cheetahs, scimitar
sea cows themselves were not cats, and short-faced bears.
Not all the “players” in trophic being hunted, they soon became
cascades are obvious or visible. extinct. Understanding how such Many of the extinctions
Some are tiny and live underground. interventions, and the introduction of occurred between 11,500 and
For example, yellow bush lupines— nonindigenous species, can damage 10,000 years ago, shortly after
plants that live on the Californian trophic cascades is vital in shaping the arrival and spread of the
coast—are consumed by the conservation measures today. ■ Clovis people, who were
caterpillars of ghost moths, which hunters. One of the most
eat the lupines’ roots. In turn, Herbivores are convincing theories about
nematodes—wormlike usually expected to be these developments is the
invertebrates—parasitize the well fed and carnivores “second-order predation
caterpillars. If these nematodes are usually expected hypothesis,” which suggests
are in the soil, they will limit the that the humans triggered a
population of caterpillars, and fewer to be hungry. trophic cascade. The people
of the lupines’ roots will be affected. Lawrence Slobodkin killed the large carnivores,
which competed with them
Extinction events for prey. As a result, predator
In extreme cases, a trophic cascade numbers were reduced
can lead to species extinction—as and prey populations rose
in the case of Steller’s sea cows, disproportionately, resulting
marine mammals that once lived in in overgrazing. The vegetation
the Bering Strait but were declared could no longer support the
extinct in 1768. It has recently been herbivores, with the result
argued that this extinction was that many herbivores starved.
caused by a calamitous trophic
Cave paintings in Altamira, Spain,
show the importance of bison to
early humans. The wild population
became extinct in 1927, but captive
herds have since been reintroduced.

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IESSCYLOASLNOTDGESIMCAARSLE

ISLAND BIOGEOGRAPHY

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146 ISLAND BIOGEOGRAPHY

IN CONTEXT

KEY FIGURES
Robert H. MacArthur
(1930–72), Edward O. Wilson
(1929–)

BEFORE
1948 Canadian lepidopterist
Eugene Munroe suggests a
correlation between island
size and butterfly diversity in
the Caribbean.

AFTER
1971–78 In the US, biologist
James H. Brown studies
mammal and bird species
variety on forest “islands” in
the Great Basin of California
and Utah.

2006 Canadian biologists
Attila Kalmar and David Currie
study bird populations on
346 oceanic islands and
discover that species variety
depends on climate as well as
area and isolation.

Unless we preserve I sland, or insular, biogeography Mangrove-fringed islands in the
the rest of life, as a examines the factors that Florida Keys—now protected for their
sacred duty, we will be affect the species richness of diverse range of marine and terrestrial
endangering ourselves isolated natural communities. life—were the focus of research to test
by destroying the home Charles Darwin, Alfred Russel the island biogeography theory.
in which we evolved. Wallace, and other naturalists had
Edward O. Wilson written about island flora and fauna pools within a dry landscape, or
in the 19th century. Their studies fragments of mountain forest
were conducted on actual islands between nonforested valleys.
in the ocean, but the same methods
can be used to look at any patch In the mid-20th century,
of suitable habitat surrounded by ecologists began more intensive
unfavorable environment that studies into species distribution
limits the dispersal of individuals. on different islands, and how and
Examples include oases in the why they varied. In the US,
desert, cave systems, city parks in biologists Edward Wilson and
an urban environment, freshwater Robert MacArthur constructed the
first mathematical model of the

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See also: Evolution by natural selection 24–31 ■ Predator-prey equations 44–49
■ Field experiments 54–55 ■ The ecosystem 134–137

Random dispersal of organisms to islands

Mainland

Island 1

Island 3 Island 2 Robert H. MacArthur
An island’s size and distance from the mainland both
affect its species richness. Islands closer to the mainland Born in Toronto, Canada, in
will receive more random dispersion of organisms; the larger 1930, and later relocating to
island gets the most, the island furthest away gets the least. Vermont in the US, Robert
MacArthur originally studied
factors at play in island ecosystems because if native species are mathematics. In 1957, he
and, in 1967, they outlined a new pushed out of prime habitat by new received his Ph.D. from Yale
theory of island biogeography. immigrants, they have a better University for his thesis
chance of finding an alternative, exploring ecological niches
Their theory proposed that each albeit imperfect (“suboptimal”) occupied by warbler species
island reflected a balance between habitat. Larger islands are also in conifer forests. MacArthur’s
the rate of new species arriving likely to have a greater variety of emphasis on the importance
there and the rate at which existing habitats or microhabitats in which of testing hypotheses helped
species become extinct. For example, to accommodate new immigrants. transform ecology from an
a habitable but relatively empty A combination of variety and lower exclusively observational
island would have a low extinction rates of extinction produces a field to one that employed
rate since there are fewer species greater species mix than on a small experimental models as well.
to become extinct. When more island—the “species-area effect.” This methodology is reflected
species arrive, competition for The actual species in the mix will in The Theory of Island
limited resources increases. At a change over time, as a result of Biogeography, which he
certain point, smaller populations colonization and extinction, but will coauthored with Edward O.
will be outcompeted, and the rate remain relatively diverse. Wilson. MacArthur received
of species extinction will rise. An awards throughout his career,
equilibrium point occurs when the Monitoring mangroves and was elected to the
species immigration rate and the In 1969, Wilson and his student National Academy of Sciences
rate of those becoming extinct are Daniel Simberloff conducted a field in 1969. In 1972, he died of
equal; this may remain constant experiment that tested the theory renal cancer. The Ecological
until a change occurs in either rate. on six small mangrove islands in Society of America awards a
the Florida Keys in the US. They biennial prize in his name.
The theory also proposes that recorded the species living there,
the rate of immigration depends then fumigated the mangroves to Key works
on the distance from the mainland, remove all the arthropods, such as
or another island, and declines with insects, spiders, and crustaceans. 1967 The Theory of Island
increased distance. The area of an In each of the next two years, ❯❯ Biogeography
island is a further factor. The larger 1971 Geographical Ecology:
it is, the lower its rate of extinction, Patterns in the Distribution
of Species

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148 ISLAND BIOGEOGRAPHY

Islands are The water acts as island of Cuba, because economic
surrounded by water. a physical barrier, sanctions since the 1960s have
preventing many species meant that fewer boats (and their
Islands are from entering or leaving. lizard stowaways) dock in Cuba.
ecological systems.
As species arrive “Island” habitats
they counted returning species and depart, island In the early 1970s, American
to observe their recolonization. populations evolve. biologist James H. Brown applied
The Florida Keys experiment the Wilson–MacArthur model to
showed that distance did indeed floating vegetation). Most of these “islands” of coniferous forest on 19
play an important role: the farther factors apply to any similar, isolated mountain ridges in the Great Basin
an island was from the mainland, habitats, not just actual islands. of California and Utah. The ridges
the fewer invertebrates returned to are separated from each other by
recolonize the area. The impact of humans—who a vast sagebrush desert. Brown
probably began visiting isolated discovered that the diversity and
New waves of immigration can, islands in the Pacific at least 3,000 distribution of small mammals
however, save even faraway island years ago—has sometimes been (excluding bats) in the isolated
species from extinction. This is dramatic. In recent centuries, forests could not be explained in
more likely to happen with certain people took dogs, cats, goats, terms of an equilibrium between
bird species—which can travel long and pigs with them when they colonization and extinction. Some
distances quickly—than with, for colonized islands in the Pacific species had become extinct, but
example, small mammals. There is and elsewhere; inadvertently, they no new species had arrived for
also the so-called target effect, also carried rats on their boats. millions of years, so Brown dubbed
where some islands are more On many islands, rats ate the eggs the mammals “relicts.” A few years
favored destinations because of the of breeding seabirds and the later, his analysis of resident bird
habitat they provide. Given the seeds of endemic plants, some of populations on the ridges revealed
choice of a treeless island and one which grew nowhere else. On the that new bird species had arrived
with woodland, a tree-nesting bird Galapagos Islands, dogs ate from larger, similar forests in the
will naturally opt for trees. tortoise eggs, native iguanas, and Rocky Mountains to the east and
even penguins. Goats competed in the Sierra Nevada to the west.
Human impact with Galapagos tortoises for food Brown concluded that certain
The key factors influencing the and wiped out up to five species of species groups—especially those
species mix on an oceanic island plant on the Santiago Islands. that fly—are more likely to be
are its degree of isolation, how long successful immigrants than others.
it has been isolated, its size, the The arrival of humans, however,
suitability of its habitat, its location has not always reduced species Destroying rainforest
relative to ocean currents, and richness on islands. Researchers for economic gain
chance arrivals (for example, discovered the important role of is like burning a
organisms washed up on mats of ship-assisted colonization of
islands in the Caribbean. Despite Renaissance painting
its relatively small size, Trinidad, to cook a meal.
for instance, has more species of
anole lizards than the much larger Edward O. Wilson