BIOGEOGRAPHY

Biogeography is the study of the geographic distribution of plants
and animals. Biogeographers try to explain why organisms are
distributed as they are.

Biogeographic studies show that life-forms in different parts of the
world have distinctive evolutionary histories.
One of the distribution patterns that biogeographers try to
explain is how similar groups of organisms can live in places separated
by seemingly impenetrable barriers. For example, native cats
are inhabitants of most continents of the earth, yet they cannot
cross expanses of open oceans. Obvious similarities suggest a common
ancestry, but similarly obvious differences result from millions
of years of independent evolution. Biogeographers also
try to explain why plants and animals, separated by geographical
barriers, are often very different in spite of similar environments.

For example, why are so many of the animals that inhabit Australia
and Tasmania so very different from animals in any other part of
the world? The major native herbivores of Australia and Tasmania
are the many species of kangaroos (Macropus). In other parts of the
world, members of the deer and cattle groups fill these roles. Similarly,
the Tasmanian wolf (tiger) (Thylacinus cynocephalus), now
believed to be extinct, was a predatory marsupial that was unlike
any other large predator. Finally, biogeographers try to explain why
oceanic islands often have relatively few, but unique, resident
species. They try to document island colonization and subsequent
evolutionary events, which may be very different from the evolutionary
events in ancestral, mainland groups. The discussion that
follows will illustrate some of Charles Darwin’s conclusions about
the island biogeography of the Galápagos Islands.
Modern evolutionary biologists recognize the importance of
geological events, such as volcanic activity, the movement of
great landmasses, climatic changes, and geological uplift, in creating
or removing barriers to the movements of plants and animals.
Biogeographers divide the world into six major biogeographic regions.
 As they observe the characteristic plants and
animals in each of these regions and learn about the earth’s geologic
history, we understand more about animal distribution patterns
and factors that played important roles in animal evolution.

Only in understanding how the surface of the earth came to its
present form can we understand its inhabitants.