Island Colonization by Lesser Antillean Birds

Abstract

--We present an analysis of bird distribution in small islands in the northern Lesser Antilles colonized principally from Guadeloupe. In spite of great differences among the islands in soils, rainfall, and vegetation, their avifaunas are strikingly uniform. We found that species inhabiting coastal scrub on the source island performed better as colonists than inhabitants of interior rainforest, suggesting that humid forests in the target islands would hold drastically impoverished bird communities. This proved not to be the case. Diversities in the small-island rainforest communities were compensated by the substitution of coastal scrub species for missing forest counterparts and the expansion of vertical foraging zones. In progressing from species-poor to species-rich communities in equivalent habitat, the number of trophic guilds re-mains constant, while the number of species per guild and the tightness of species packing increase. We conclude that the faunal uniformity of islands colonized from Guadeloupe results from nonuniform dispersal abilities coupled with ordering ecological constraints: versatility in habitat occupancy, trophic status and size in relation to guild neighbors. MODERN biogeography has enjoyed considerable success in accounting for the numbers of species of birds, lizards, and other taxa found on the islands of various archipelagoes. Nearly all the interisland variation in bird species numbers in the southwest Pacific, for example, can be explained by a simple empirical formula that takes into account each island's area, elevation, and distance from New Guinea, the ultimate source of colonists in that region (Diamond 1973). Equilibrium theory (MacArthur and Wilson 1963) maintains that insular faunas are stabilized by a dynamic balance of colonizations and extinctions, and suggests the statistical limits within which the number of species should vary on any given island. However, equilibrium theory tells us nothing about how different or how alike the faunas of