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 Galdpagos 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.