Quaternary climate change and the geographic ranges of mammals.

A species' range can be a proxy for its ecological well-being. Species with small and shrinking range distributions are particularly vulnerable to extinction. Future climate change scenarios are predicted to affect species' geographical extents, but data on how species' distributions respond to changing climate are largely anecdotal, and our understanding of the determinants and limits to species geographic ranges is surprisingly poor. Here we show that mammal species in more historically variable environments have larger geographical ranges. However, the relationship between range size and long-term climate trends cannot be explained by variation in our estimates of habitat specificity. We suggest that large oscillations in Quaternary temperatures may have shaped the contemporary distribution of range sizes via the selective extirpation of small-ranged species during glacial expansion and/or recolonization by good dispersers after glacial retreats. The effect of current climate change on species' distributions and extinctions may therefore be determined by the geographical coincidence between historical and future climate scenarios, the "mesh size" of the extinction/dispersal filter imposed by past climate change, and whether similar ecological and evolutionary responses to historical climatic change are appropriate in an increasingly transformed and fragmented landscape.