The Ecology Book

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 ■ Ecologica l resilience 150 –151

ECOSYSTEMS

same time as releasing oxygen.

This process, photosynthesis, is the

first step towards creating food. In

places where there is no sunlight,

organisms producing their own

food are called chemotrophs. Those

in the deep ocean, for example, get

the energy they need from chemicals

released by hydrothermal vents.

Animals that eat producers and

creatures that eat other animals are

called consumers, or heterotrophs.

There may be two, three, or more

levels of these in any particular part

of the food chain, but there is always

a producer at the bottom, and all

levels above it are consumers.

Animals that only eat plants are

herbivores, or primary consumers,

and they include cattle, rabbits,

butterflies, and elephants. Those

that eat only other animals are

carnivores, or secondary consumers;

these include thrushes, dragonflies,

and hedgehogs. In turn, secondary

consumers may be eaten by larger

predators, or tertiary consumers,

such as foxes, small cats, and birds

An apex predator, such as the bronze

whaler shark, has no natural predators.

In the temperate waters of the ocean

off South Africa the shark can find vast

quantities of sardines to eat.

of prey. The animals at the top of

their food chain are apex predators.

They include consumers such as

tigers, killer whales, and golden

eagles that are not preyed upon

by other animals.

The food chain does not break

when plants and animals die.

Detritus feeders (detritivores) prey

on the remains, recycling nutrients

and energy for the next generation

of producers to use.

Food webs

Observers after Bradley suggested

that animals were not simply part

of a food chain, but a larger and

more complex “food web” that

comprises all the food chains in a

location. This idea was put forward

by Dutch naturalist John Bruckner

in 1768, and later taken up by

Charles Darwin, who called the

variety of connected feeding

relationships between species

a “web of complex relations”. ■

Each species has a

specific place in nature,

in geographic location

and in the food chain.

Carl Linnaeus

Richard Bradley

Born around 1688, noted British

botanist Richard Bradley gained

patrons after writing a Treatise

of Succulent Plants at the age of

22. With no university education,
    he was nonetheless elected a
    Fellow of the Royal Society and
    later became the first professor
    of botany at Cambridge.
    Bradley’s research interests
    were wide-ranging, including
    fungal spore germination and
    plant pollination. In some cases,
    Bradley was ahead of his time;
    he argued, for example, that

infections were caused by tiny

organisms, visible only with a

microscope. His investigations

into the productivity of rabbit

warrens and fish lakes led to

his theories about predator–prey

relations. Bradley died in 1732.

Key works

1716 –27 The History of

Succulent Plants

1718 New Improvements in

Planting and Gardening

1721 A Philosophical Account of

the Works of Nature

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