Qualitative Patterns of Avian Extinction on Neotropical Land-Bridge Islands: Lessons for Conservation

(1) Previous application of island biogeographic theory to the design of nature preserves has focused primarily on the number of species that can survive in a given area with time. (2) Here I examine qualitative patterns in Neotropical land-bridge island avifaunas to show the extent to which we can predict the types of species that will survive in bird communities of varying size. (3) Each avian family shows consistent differences in its representation in mainland regions or on islands, in accordance with the total size of the avifauna present. Regressions of these data allow us to predict the smallest community in which a family member can exist. (4) Distribution patterns within families show that species with wide ranges tend to survive on land-bridge islands in disproportionate numbers. This bias in survival ability would lead to increased convergence in preserved avifaunas. (5) With these qualitative patterns and previously described quantitative formulas for extinction rates we should be able to predict both the rate of species extinction on a preserve and the species most extinction prone. Application of this knowledge on a regional basis might allow us to design an optimal system of refuges.