Patterns of distribution, diversity and endemism in Afrotropical birds

Abstract

Patterns of distribution, diversity and endemism for 1595 species and well‐marked subspecies of Afrotropical (excluding marine islands) passerine and non‐aquatic non‐passerine birds are identified and analysed using uni‐ and multi‐variate statistical methods. Patterns of distribution are well predicted by a hierarchical model of African avifaunal zones based on patterns of distribution and evolution in guineafowl (Family Numididae). The boundaries of avifaunal zones recognized here for passerines and non‐passerines are similar to one another, and largely parallel those of broad contemporary vegetation types along a rainfall gradient. However, there are interesting discrepancies between the distributions of contemporary vegetation types and inferred avifaunal zones, most notably the disjunct similarity of the avifaunas of three sections of lowland forest, much of which presently is an apparently continuous belt. We interpret this disjunct avifaunal similarity in the light of palaeoecological and geomorphological data as evidence in favour of the hypothesis of forest refugia. This hypothesis states that presently continuous forests were fragmented during arid conditions in the geological past, and that birds which prefer forested biotopes were confined to “island” forest refugia. Patterns of diversity and endemism, when considered together with patterns of distribution, also support the refugium hypothesis, and suggest the existence of two additional refugia, one in the western African forest, the other in the eastern African equatorial savanna. Several of these refugia may have been important centres of evolution for forest and open country birds.