The Science Book

134 ALEXANDER VON HUMBOLDT

By the end of the 19th century, the
first university course in ecology
was being taught by the Danish
botanist Eugenius Warming,
who also wrote the first ecology
textbook Plantesamfund (Plant
Ecology) in 1895. From Humboldt’s
pioneering work, Warming
developed the global geographical
subdivision of plant distribution
known as biomes, such as the
tropical rain-forest biome, which
are largely based on the interaction
of plants with the environment,
especially climate.

Individuals and community
Early in the 20th century, the
modern definition of ecology
developed as the scientific study
of the interactions that determine
the distribution and abundance
of organisms. These interactions
include an organism’s environment,

encompassing all those factors that

influence it—both biotic (living

organisms) and abiotic (nonliving

factors such as soil, water, air,

temperature, and sunlight). The

scope of modern ecology ranges

from the individual organism to

populations of individuals of the

same species, and the community,

made up of populations that share

a particular environment.

Many of the basic terms and

concepts of ecology came from the

work of several pioneer ecologists

in the first few decades of the 20th

century. The formal concept of the

biological community was first

developed in 1916 by the American

botanist Frederic Clements. He

believed that the plants of a given

area develop a succession of

communities over time, from

an initial pioneer community to an

optimal climax community within

which successive communities

of different species adjust to one

another to form a tightly integrated

and interdependent unit, similar

to the organs of a body. Clements’

metaphor of the community as a

“complex organism” was criticized

at first but influenced later thinking.

The idea of further ecological

integration at a higher level than

the community was introduced

in 1935 with the concept of the

ecosystem, developed by the

English botanist Arthur Tansley.

An ecosystem consists of both

living and nonliving elements.

Their interaction forms a stable

unit with a sustaining flow of

energy from the environmental

to the living part (through the food

chain) and can operate on all

scales, from a puddle to an ocean

or the whole planet.

Studies of animal communities

by the English zoologist Charles

Elton led him to develop in 1927 the

concept of the food chain and food

cycle, subsequently known as the

“food web.” A food chain is formed

by the transfer of energy through an

ecosystem from primary producers

(such as green plants on land)

through a series of consuming

A food chain transfers energy from primary

producers (plants and algae that convert the Sun’s

energy into food energy) to consumer organisms that

eat the plants (such as rabbits and other herbivores),

and then to the predators that feed on the consumers.

This whole chain of

poisoning, then, seems

to rest on a base of minute

plants which must have been

the original concentrators.

Rachel Carson

Lion, an apex

predator (not preyed

on by others)

Kite

Snake Mouse

Owl

Jackal

Wild cat

Rabbit

Green

plants

Goat