Seasonal dynamics of small mammal populations: resource availability and cold exposure interact to govern abundance

Organisms in seasonal environments respond to both resources in the summer and environmental conditions in winter. Small mammals, in particular, respond quickly to changes in their environment, with many species reliant on the thermal refuge of the subnivium in the winter. However, there has been little research exploring how resources and cold exposure drive the seasonal dynamics of small mammal populations. We studied the populations of 3 subnivium-specialist small mammal species in seasonally snow-covered forests in Wisconsin USA across 5 years during summer and winter. In summer, mast availability and canopy cover governed white-footed mouse (Peromyscus leucopus (Rafinesque, 1818)) populations, coarse woody debris drove short-tailed shrew (Blarina brevicauda (Say, 1823)) populations, and rainfall influenced red-backed vole (Myodes gapperi (Vigors, 1830)) abundance. Dietary analysis via stable isotopes revealed that shrews primarily consumed arthropods, and mice predominately consumed hard mast despite interannual changes in availability. In winter, white-footed mice and red-backed vole abundances were negatively related to cold exposure. Short-tailed shrew winter population was positively related to their abundances the previous summer. These small mammals responded to species-specific drivers during the growing and snow seasons. Consequently, shorter snow seasons from climate change appear to be restructuring communities by creating a less hospitable environment for winter-adapted species, likely contributing to their regional declines.