The impact of population processes on patterns of species richness: Lessons from elevational gradients

Abstract

Abstract In the last few years, considerable headway has been made towards understanding patterns of species richness along latitudinal and elevational gradients, mostly by focussing on the influences of surface area, climatic factors, evolutionary history, and stochastic processes. However, the potential impact of population-level processes in determining or modifying patterns of species richness has largely been neglected, partly due to the difficulty of gathering such data for numerous species along geographical or ecological gradients. Based on two empirical examples, I here show that dispersal and the resulting source-sink effects modify patterns of plant species richness along elevation gradients, and that the inclusion or exclusion of such sink populations alters the perception of the diversity patterns and hence our interpretation of them. I argue that population processes should be taken into account when studying patterns of species richness, especially at scales at which dispersal is common in the taxon under consideration.