The Ecology Book

112 ANIMAL ECOLOGY

overlap. If different species live in

the same habitat and have similar

lifestyles, they will be in

competition but they may be able

to live in close proximity if some

aspects of their behavior or diet

differ. This arrangement is known

as niche partitioning. For example,

various anole lizards on Puerto

Rico successfully occupy the same

areas because they select perching

locations in different parts of trees.

There are limits to niche

overlap. When two animals with

identical niches live in the same

place, one will drive the other

to extinction. This concept—the

competitive exclusion principle—

was outlined by Joseph Grinnell

in 1904 and developed in a paper

published by Russian ecologist

Georgy Gause in 1934, becoming

known as Gause’s law.

Pyramid of numbers

Charles Elton used a pyramid as

a way of graphically representing

the different levels in a food chain,

with the producers at the bottom,

the primary consumers on the

level above, and so on. Often, the

primary consumers—insects,

in particular—will outnumber the

producers, but the higher levels

of consumers will become less

numerous toward the top of the

pyramid. This system does not

take account of parasites; fleas

and ticks on mammals and birds

will far outnumber the total of all

the vertebrates in an ecosystem.

In 1938, German-born animal

ecologist Frederick Bodenheimer

modified Elton’s pyramid of

numbers to produce a pyramid

of biomass that represented the

amount of living matter in a given

area at every level. This took

into account the fact that some

organisms are much larger than

others, but because it showed

comparative biomasses at a fixed

point in time, it produced anomalies.

For example, in a pond, the mass

of the phytoplankton producer

(microscopic organisms that are the

foundation of the aquatic food web)

may not be as great as the mass of

the fish consumers at a particular

point in time, so the pyramid

will be inverted. However,

phytoplankton reproduce quickly

Microscopic organisms, including

these diatoms, form a significant part

of all ecological pyramids. Their huge

numbers and rapid reproduction

provide mass and energy for the

species higher up the pyramid.

Three major

types of ecological

pyramid

Ecological pyramids represent

quantifiable data in an ecosystem.

Numbers show the population size of

individual species in a trophic level;

biomass, their relative presence; and

energy, who eats what and how much.

Pyramid

of numbers

Pyramid

of biomass

Pyramid

of energy

10,000

Freshwater shrimp

1,000

Bleak

100

Perch

10

Northern pike

1

Osprey

Grass

18 million lb per sq mile

Snowshoe hare

17,000 lb per sq mile

Red fox

1,700 lb

per sq mile

Wolf

340 lb

per sq mile

Producers

100%

Herbivores

10%

Carnivores

1%

Secondary

carnivores

0.1%

Apex

predators

0.01%

The basic process in

trophic dynamics is the

transfer of energy from

one part of the ecosystem

to another.

Raymond Lindeman

US_106-113_Animal_Ecology.indd 112 12/11/2018 17:34