One of the fundamental concepts of evolution and ecology, the theory of island biogeography was first developed in the 1960s by scientists E.O. Wilson and Robert MacArthur. The basic theory says that on larger islands there is a larger number of species, while smaller islands have less species diversity.
The Basic Explanation of Island Biogeography
Island biogeography doesn't just involve islands. In the theory, an "island" can be any ecosystem that is different from the ecosystems around it, such as an oasis in the desert or a small rainforest surrounded by farmland.
Every island has an equilibrium for the optimum number of species it can support. Species diversity on an island mainly depends on three things:
- Extinction, how many species die out over time
- Immigration, how many new species move to the island from neighboring islands or landmasses
- Emigration, how many species leave the island to settle elsewhere.
Other things that affect species diversity include time, isolation, and climate. The distance of an island or other isolated habitat from other habitats is an important contributor to the levels of immigration and emigration. For example, an island close to a large mainland will have more animals arriving from the mainland to colonize the island than an isolated island many miles from other land will.
Later expansions of the theory of island biogeography have begun to take into account other aspects of the distribution of species in isolated areas, including looking at animal body size and the effects of human activity on the species diversity of a given area.
The Implications of Island Biogeography
Modern science uses island biogeography theory to understand species today and to help endangered species.
The theory of island biogeography is important to conservation biology because it helps scientists predict how many species should thrive in a given area and gives them information on how to develop protective reserves.
Another influence island biogeography has had on conservation biology is the development of habitat corridors, thin strips of habitats connecting two similar areas that would otherwise be isolated as islands in the middle of development or farmland. These habitats are believed to increase the effective size of the two habitats, allowing them to act as one island and therefore increase the number of species the area can support. It also helps support larger species, since the larger connected landmass allows for animals such as bears, wolves, and many big cats which will only inhabit an area with a significant range for them to roam.
Overall, island biogeography is an important concept that helps people understand species distribution around the world and assists in the preservation of ecosystems and the animals in them which might otherwise be lost.
Further Reading about Island Biogeography:
MacArthur, Robert H., and Edward O. Wilson, The Theory of Island Biogeography. Princeton University Press, 2001
Spellerberg, Ian F., J. William, and D. Sawyer, An Introduction to Applied Biogeography. Cambridge University Press, 1999
Quammen, David . The Song of the Dodo: Island Biogeography in an Age of Extinctions. Simon & Schuster, 1997
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