Environmental Factors Affecting the Landscape-Scale Spatio-Temporal Distribution of Small Mammal Assemblages Across the Northern Great Plains of North America

Abstract

The logistic constraints of traditional sampling methods have limited our understanding of the effects of landscape-scale factors on the spatiotemporal distributions of rodents and shrews (small mammals), particularly in heterogeneous landscapes. I used owl pellets as an alternative sampling method, from which the remains of 60,972 individuals were identified and quantified in samples collected across 4.3 million hectares over 15 years. These remains were used to examine the influence of landscape-scale environmental factors on the spatial composition and annual abundances of small mammal species. I hypothesized that the spatial distribution of soil characteristics, agricultural land use, and weather patterns would largely determine the distributions of grassland small mammals within their geographic ranges, while annual weather variation would largely influence the temporal dynamics of grassland rodents across the landscape. I found soil texture was the primary landscape feature driving small mammal composition across my study area, whereas agricultural cropland significantly altered the composition of these assemblages. Cropland with clay soils was dominated by deer mice (Peromyscus maniculatus), whereas areas with higher proportions of native grassland and moderately sandy soils supported communities with more sagebrush voles (Lemmiscus curtatus). Areas with clay soils and higher annual precipitation were associated with higher proportions of house mice (Mus musculus), meadow voles (Microtus pennsylvanicus), and shrews (Blarina brevicauda and Sorex species), whereas drier areas with sandier soils and lower annual precipitation were dominated by olive-backed pocket mice (Perognathus fasciatus) and northern grasshopper mice (Onychomys leucogaster). Furthermore, I found variation in weather had little influence on deer mouse or sagebrush vole annual abundance, indicating that other factors (i.e., habitat availability) are more responsible for changes in the abundance of these species at the landscape scale. In contrast, meadow voles were positively associated with the duration of snow cover above the hiemal threshold (i.e., 20 cm), exhibiting up to five-fold increases (i.e., irruptions) in abundance following winters of persistent, deep snow cover. This is the largest study in spatial scale ever conducted on grassland small mammals, which provides a truly landscape-scale look at the environmental factors affecting their spatial composition and long-term, population-level responses to environmental change.