Changes in small mammal communities throughout the late Quaternary across eastern environmental gradients of the United States

Distributions of biotas are predictably structured along environmental gradients. Vegetation is primarily restricted by precipitation and temperature, whereas, most mammals are limited by both climate and vegetation (i.e., habitats). Consequently, climate change in the late Quaternary has affected the composition of mammal communities along environmental gradients. To evaluate these impacts at the biome scale, 211 late Quaternary (20,000–500 cal yr BP) mammal faunas from two modern biome regions east of the Rocky Mountains were compared using non-metric multidimensional scaling. Communities came from temperate grassland deserts (TGD) and seasonal forests (TSF). Here, we focus on overall changes in community composition and diversity, and the broader impacts along longitudinally and latitudinally structured moisture and temperature gradients, respectively. Compositional turnover of Pleistocene communities follows a broad and gradual longitudinal gradient, with moisture decreasing to the west as it does today. However, Pleistocene TSF faunas are more diverse and compositionally distinct from those of the Holocene, while TGD communities are compositionally similar throughout the late Quaternary. Clear boundaries (narrow ecotones) marking the turnover along longitude between TGD and TSF are identified in the Holocene. Across latitude, we find greater spatial turnover in the late Pleistocene, indicating that Pleistocene temperature gradients were significantly stronger than in the Holocene. We interpret these faunal differences to be consistent with greater patchiness in the Pleistocene supported by more pronounced environmental heterogeneity. Non-analog faunas may be a manifestation of stronger Pleistocene gradients, patchiness, and greater spatial community turnover. The “flickering” of the Pleistocene climate in contrast to the stability of the Holocene may have been the primary driver of these differences.