LINKING HOLOCENE ABUNDANCE DYNAMICS AND CLIMATE FOR WESTERN SMALL MAMMALS

Forecasting how species will respond to ongoing environmental change is a priority for conservation and requires knowledge of the processes that have shaped community dynamics in the past. Here we evaluate how contrasting local paleoclimates have shaped the dynamics of small-mammal communities in the western United States through the Holocene, with reference to the geographic affinity and dietary functional groups of species. A basic prediction is that species respond to warming by poleward shifts in their geographic range. We therefore expect an increase in the richness and abundance of species with a southern geographic affinity at a given locality. Our community-level findings suggest an inverse relationship between overall rarefied species richness and climate warming, but a positive response in the richness and dominance of species with a southern geographic affinity. However, species-level abundance-climate relationships are variable and poorly explained by a species’ geographic affinity within a given site. Nevertheless, species shared across sites exhibit markedly similar responses to climate. An analysis of functional groups reveals the importance of species life-histories in driving responses to climate: granivores show a consistently positive relationship with warming, while omnivores show a consistently negative relationship. Regression tree analyses revealing how functional- species- and community-level responses are coupled show remarkable concordance across sites, indicating that dietary functional group effects exceed those of geographic affinity in driving community responses to climate warming.