ECOLOGICAL BIOGEOGRAPHY OF AFRICAN MAMMALS IN RELATION TO CLIMATE AND TOPOGRAPHY

The ecological biogeography of modern mammals provides a means to link mammal diversity to past environments and to predict ecological responses to future climate change. For North American mammals, species richness and ecological diversity (in body mass and trophic categories) at the continental scale are predicted well by climatic and topographic variables. We evaluated the ecological biogeography of modern African mammals in relation to climate and physiography with a focus on species richness. African mammals may respond differently than North American mammals to environmental gradients because Africa is dominated by different mammalian clades that did not experience major Quaternary extinction, has no recent history of continental ice sheets, and has different spatial distributions of physiography and climate. We compiled geographic ranges for 1325 species of extant African mammals and analyzed species richness over an equal-area grid. For each quadrat of 150 by 150 km, we also compiled four climatic and two topographic variables. A latitudinal gradient in species richness is evident in both hemispheres, but the northern-hemisphere gradient is steeper and less variable, reaching a low in the Sahara region and rising again in northern Africa. Overall, the African latitudinal gradient is more variable than that in North America. A significant multiple regression model with five predictors (mean annual precipitation, elevation, PET, mean annual temperature, AET) explains 71.9% of the variance in species richness across Africa. Ordination of environmental variables separates quadrats that contrast in available moisture (PC1, 79.8% of variance) and those that contrast in topography (PC2, 17.6% of variance). Species richness exhibits a strong positive, exponential relationship with scores on PC1 (R²=0.86), suggesting a strong dependence of richness on available moisture. In contrast, North American mammalian species richness is more closely tied to temperature seasonality. In both continents the highest species richness occurs in regions of high elevation, such as rift-valley highlands. Our results suggest that past changes in precipitation were important controls on mammalian diversity and future changes will affect the distribution of African mammals.