African Primate Assemblages Exhibit a Latitudinal Gradient in Dispersal Limitation

Recent studies have demonstrated that dispersal limitation, which refers to the limited ability of individuals to reach distant geographic areas, is an important influence on the species that are found in primate assemblages. In this study, we investigate the relative influences of dispersal limitation and environmental filtering in 131 African primate assemblages in 9 biogeographic regions throughout sub-Saharan Africa. Specifically, we evaluate the dispersal-ecological specialization hypothesis, which posits that there are trade-offs between dispersal ability and ecological specialization that are influenced by climatic variation along latitudinal gradients. The hypothesis predicts that species in assemblages near the equator, where climatic conditions are more stable, will exhibit stronger dispersal limitation and greater ecological specialization than species within assemblages located further from the equator, where climate is more variable. In contrast, assemblages located at higher latitudes are expected to be influenced more strongly by environmental filtering than dispersal limitation. We used hierarchical cluster analysis to identify regions, conducted partial Mantel tests to evaluate the contributions of dispersal limitation and environmental filtering in each region, and evaluated predictors of those contributions with linear regression. In all regions, dispersal limitation was a stronger predictor of community similarity than was environmental filtering, yet the strength of dispersal limitation varied. Dispersal limitation was greatest at low latitudes and declined with increasing absolute latitude. Thus, primate assemblages exhibited a significant latitudinal gradient in dispersal limitation, but not in environmental filtering. These results support aspects of the dispersal-ecological specialization hypothesis and call for future mechanistic studies to address this broad-scale pattern.