The Ecology Book

201

All of Siberia is in the Palearctic

region, and the Siberian

white birch trees depicted here are

part of a subdivision called the East

Siberian taiga.

THE LIVING EARTH

From 1848, Wallace conducted

years of fieldwork in South America

and Southeast Asia. He researched

the feeding and breeding behavior

and migratory habits of thousands

of species, paying specific attention

to animal distribution compared

with the presence or absence of

geographical barriers, such as seas

between islands. He concluded that

the number of organisms living in a

community depends on the food

available in that specific habitat.

Wallace’s Line

During his 1854–62 expedition

to the Malay Archipelago, Wallace

collected an astonishing 126,000

specimens, many of them from

species unknown to Western

science, including 2 percent of the

world’s bird species. He regarded

biogeography as support for the

theory of evolution by means of

natural selection. One of Wallace’s

important findings was the marked

difference in bird species on either

side of what was to become known

as the Wallace Line, which runs

along the Makassar Strait (between

the islands of Borneo and Sulawesi)

and the Lombok Strait (between

Bali and Lombok); this separates

Asian fauna from the Australasian.

He found that larger mammals and

most birds did not cross the line.

For example, tigers and rhinos live

only on the Asian side; babirusas,

marsupials, and sulfur-breasted

cockatoos only on the other side.

He also highlighted the sharp

differences between animals in

North and South America.

In 1876, Wallace proposed six

separate zoogeographic regions:

Nearctic (North America); Neotropics

(South America); Palaearctic

(Europe, Africa north of the Sahara

Desert, and Central, North, and East

Asia); Afrotropics (Africa south of

the Sahara Desert); Indomalaya

(South and Southeast Asia); and

Australasia (Australia, New Guinea,

and New Zealand). Today Wallace’s

regions, with the addition of

Oceania (the islands of the Pacific

Ocean) and Antarctica, are known

as biogeographic realms. ■

See also: Evolution by natural selection 24–31 ■ Island biogeography 144–149

■ The distribution of species over space and time 162–163 ■ Biomes 206–209

Alfred Russel Wallace

Explorer, naturalist, biologist,

geographer, and social

reformer Alfred Russel

Wallace left school at 14,

and trained as a surveyor

in London before becoming

a teacher. He became

fascinated with insects after

meeting British entomologist

Henry Bates. The pair

ventured to the Amazon

Basin in 1848 on a four-year

collecting expedition. Trips to

the Orinoco River and the

Malay Archipelago followed.

Wallace arrived at the same

conclusion as Charles Darwin

on the origin of species by

natural selection, and they

presented their papers jointly

in 1858. A world authority on

fauna distribution, Wallace

also raised awareness about

problems caused by human

impact on the environment.

Key works

1869 The Malay Archipelago

1870 Contributions to the

Theory of Natural Selection

1876 The Geographical

Distribution of Animals

1878 Tropical Nature, and

Other Essays

1880 Island Life

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