Geographic range shapes influence species richness in global hotspots

The extraordinary richness of species in tropical mountain regions is often attributed to aggregations of small-ranged species, allowing tight spatial packing of their ranges. However, ranges of species in these regions are also distinctly more patchy and elongated than those found in adjacent lowlands. Our global analysis of mainland birds demonstrates that these range shapes augment the spatial variation in species richness. Both the linearity and patchiness of species ranges are most pronounced in aseasonal and topographically complex regions, most notably in the tropical Andes, where these range shapes contribute more to the pattern of species richness than broad-scale variations in range size. Consequently, niche-based processes that govern the spatial configuration of habitats contribute to patterns of species richness in global hotspots over and above the processes that affect species richness through range sizes.