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.

Patterns of species richness and narrow endemism of terrestrial bird species in the Afrotropical region

“…The results of this study generally corroberate those of Crowe & Crowe (1982), which due to the coarser geographical scale of analysis did not identify certain species richness peaks identified here, namely the Ethiopian highlands, the mountains from the Eastern Arc to the Chimanimani's, the Congo-Zambezi watershed (Lake Upemba-Mitumba mountains, Marunga and Mwinelunga centres) and mountains in West Africa. Pomeroy (1993) and the Endemic Bird Area (EBA; ICBP, 1992; Stattersfield et al, 1998) study highlight all of these peaks.…”

“…This study found high correlation of overall species richness patterns between passerines and nonpasserines, as did Crowe & Crowe (1982), and Pomeroy (1993). However, peaks of species richness show only roughly 50% correlation.…”

“…These different data types all have inherent shortcomings. As a result of the constraints of large gaps in point data for the Afrotropics, particularly in some of the former French territories in West Africa, northern Mozambique and eastern Angola Crowe & Crowe, 1982), it was decided to use conservatively developed range maps based on point data presented in the Atlases of Speciation and numerous other published sources (see Appendix) using current knowledge of habitat requirements and specificity. Careful attention was paid to possible discontinuities in ranges resulting from local habitat changes (e.g.…”

Biogeographical patterns of endemic terrestrial Afrotropical birds

“…Although non-passerines do not form a monophyletic group, non-passerine (n = 427) and passerine (n = 1010) species are analysed as two subsets of the Afrotropical endemics, to facilitate comparison with results of Crowe & Crowe (1982). Distributional data for these endemic terrestrial Afrotropical bird species were digitized as putative presence within 1 × 1 degree grid cells (c. 110 × 110 km) using Worldmap Software (Williams, 1997).…”

“…The study of patterns of bird species distribution has a long history in Africa, ranging from the descriptive accounts by Chapin (1923Chapin ( , 1932 and Moreau (1966) to the use of multivariate techniques by Crowe and coworkers (terrestrial Afrotropical birds: Crowe & Crowe, 1982; Afrotropical waterbirds: Guillet & Crowe, 1985), Stuart et al (montane forest birds, 1993), Diamond and coworkers (Afrotropical forest birds: Diamond & Hamilton, 1980;Diamond, 1985) and Williams et al (1999). Using another approach Fjeldså and coworkers (Fjeldså, 1993(Fjeldså, , 1994Fjeldså & Lovett, 1997) used genetic distance based on the DNA/DNA hybridization data to distinguish areas where ancient species persist from those where diversification is more intense or recent.…”