Determining the influence of continental species-richness, island availability and vicariance in the formation of island-endemic bird species

Abstract

Using a data set composed of all known island-endemic bird species, we demonstrate that taxonomic differences in island-endemic diversity are real and significantly greater than those predicted by a null model in which island-endemic species are randomly distributed across families. We propose on the basis of a simple model of peripheral isolate speciation that these differences might be partly explicable in terms of differences in the number of continental species in an avian family, the number of islands in the vicinity of the continental range of an avian family, and the relative abundance of the types of island (oceanic v. continental) in the vicinity of the continental range of the avian family. There are significant positive associations between (i) the number of island-endemic species in an avian family and the numbers of continental species in that family, and (ii) between the number of island endemic species and the number of islands in the vicinity. Island type did not account for a significant amount of the variance in numbers of island-endemic species between families. While this regression analysis explains a significant amount of the variance among families, over 50% remains unexplained. Expanding the model to incorporate the effects of behavioural, life-history and morphological parameters may account for a significantly greater proportion of the total variance among families. © 1996 Blackwell Science Ltd.