Cooperative Fish and Wildlife Research Units Program: Michigan
Education, Research and Technical Assistance for Managing Our Natural Resources

The assembly of species into communities and ecoregions is the result of interacting factors that affect plant and animal distribution and abundance at biogeographic scales. Here, we empirically derive ecoregions for mammals to test whether human disturbance has become more important than climate and habitat resources in structuring communities. We analyzed data from 25 mammal species recorded by camera traps at 6,645 locations across the conterminous United States in a joint modeling framework to estimate relative abundance of each species. Climate was the most important predictor of mammal abundance overall, while human population density and agriculture were less important, with mixed effects across species. Seed production by forests also predicted mammal abundance, especially hard-mast tree species. We used a clustering analysis to describe eight broad and 16 narrow mammal communities. The mammal maps are similar to those of plants, with an east-west split driven by different dominant species of deer and squirrels. Communities vary along gradients of temperature in the east and precipitation in the west. Most fine-scale mammal community boundaries aligned with established plant ecoregions and were distinguished by regional specialists or shifts in the relative abundance of widespread species. Maps of potential ecosystem services provided by these communities suggest high herbivory in the Rocky Mountains and eastern forests, high invertebrate predation in the subtropical south, and greater predation pressure on large vertebrates in the west. Our results highlight the importance of climate to modern mammals and suggest that climate change will have strong impacts on mammal communities in the future.