Equilibrium Theory of Island Biogeography and Ecology

Abstract

Department of Biological Science, Florida State University, Tallahassee, Florida 32306THE BIOLOGICAL IMPORTANCE OF ISLANDSOceanic islands and archipelagoes are intrinsically important to biologists; 5% ofthe land surface of the earth is insular, and if South America, which has been anisland throughout most of its existence, is included the figure rises to 19%. Signifi-cant portions of the evolutionary histories of many economically and biologicallyimportant species occurred on oceanic islands, and if the earth were not liberallysprinkled with isolated bits of land in addition to the world continent, its biotawould be much poorer.But the intrinsic importance of islands, scientific or economic, has not inspiredthe intense research in island biogeography which justifies this review of recentadvances. Rather it is the realization that oceanic islands are paradigms for geo-graphic entities ranging in size from tiny habitat patches (52, 53) to continents (86,92, 112) or even the entire earth (74). It is almost a platitude that Darwin’s observa-tions in the Galapagos Archipelago and Wallace’s in the Malay Archipelago crystal-lized the then nascent concept of organic evolution by natural selection (13, 110),and many other classical evolutionary advances rest originally on insular observa-tions. Because islands are so clearly isolated from other land masses, island popula-tion data contributed heavily to the realization that most speciation is allopatric(54). Wallace’s Malaysian observations allowed strong inferences about changingsea levels, past land connections, and the position of a line separating two greatbiogeographic provinces (110). Insular isolation is important ecologically becauseit allows us to be virtually certain that an organism encountered on an island is atrue nesiote. Consequently, problems in Community structure and function, such asthe distribution of individuals into species or the trophic relationships among popu-lations, are more readily attacked in an island setting; any organism found there isassuredly a member of the biotic community.161