Diversification of African greenbuls in space and time: linking ecological and historical processes

The process of diversification of African forest birds since the upper Tertiary can be illustrated by linking together a well-resolved phylogeny and species distribution for the 65 species of African greenbuls (Pycnonotidae, exculsive bulbuls). The geographical pattern of species richness and of branch-length sums resembles the general forest biodiversity pattern, with richness peaks corresponding to postulated Pleistocene forest refuges. However, closer examination reveals that this is caused by the disproportionately high contribution of data points representing old and widespread species. Most of the recently evolved species have tiny geographical ranges, mostly in the montane areas, and therefore contribute little to the overall picture. It is suggested that speciation may generally take place in topographically well-structured areas but that species distributions are gradually shifted towards productive lowland areas as a consequence of long-term range dynamics.