Environmental heterogeneity predicts global species richness patterns better than area

Abstract

Aim: It is widely accepted that biodiversity is influenced by both niche-related and spatial processes from local to global scales. Their relative importance, however, is still disputed, and empirical tests are surprisingly scarce at the global scale. Here, we compare the importance of area (as a proxy for pure spatial processes) and environmental heterogeneity (as a proxy for niche-related processes) for predicting native mammal species richness world-wide and within biogeographical regions. Location: Global. Time period: We analyse a spatial snapshot of richness data collated by the International Union for Conservation of Nature. Major taxa studied: All terrestrial mammal species, including possibly extinct species and species with uncertain presence. Methods: We applied a spreading dye algorithm to analyse how native mammal species richness changes with area and environmental heterogeneity. As measures for environmental heterogeneity, we used elevation ranges and precipitation ranges, which are well-known correlates of species richness. Results: We found that environmental heterogeneity explained species richness relationships better than did area, suggesting that niche-related processes are more prevalent than pure area effects at broad scales. Main conclusions: Our results imply that niche-related processes are essential to understand broad-scale species–area relationships and that habitat diversity is more important than area alone for the protection of global biodiversity.