CHANCE, HABITAT AND DISPERSAL IN THE DISTRIBUTION OF BIRDS IN THE WEST INDIES.

Abstract

New approaches to the analysis of insular communities have stimulated a strong revival of interest in the field of biogeography (Preston, 1960; MacArthur and Wilson, 1963, 1967; Hamilton et al., 1964). Of the many problems associated with the determination of insular faunas, the one of how the number of species within a taxonomic group is regulated has proven most amenable to theoretical abstraction (MacArthur and Wilson, 1967). A carefully conducted empirical test has subsequently confirmed many predictions of the equilibrium theory, and places on a solid footing the idea that the number of species on islands is regulated by a balance of immigration and extinction rates (Simberloff and Wilson, 1969). The importance of these fundamental processes in island biogeography seems well enough established that it is now of interest to build upon them as assumptions in seeking to extend the analysis. In this paper I will explore two problems in the distribution of West Indian birds. The first involves the degree of determinism in insular faunas. How accurately can the list of species present be predicted from a knowledge of easily recorded ecological features, i.e., an island's location in relation to sources of colonists, size and range of habitats? The second concerns the regulation of sympatry within adaptively related groups of species as a function of faunal size.