Late Wisconsin mammalian faunas and environmental gradients of the eastern United States

Small mammal species distribution, density, and composition of modern and Pleistocene faunas from the eastern United States provide information about environmental gradients. Higher summer temperatures and less effective moisture along a transect from the northeast to the southwest can be correlated with the distribution of small mammals as well as decreases in the total number of shrew and vole species. Relative frequencies of “boreal”, “deciduous”, and “steppe” species are more equal in late Wisconsin than modern faunas which are predominantly composed of only one group. A higher vole species density is prevalent in each late Wisconsin fauna and eleven of twelve of these faunas have a higher shrew species density than the corresponding modern fauna. Many shrew and vole species that are today endemic to the boreal provinces were cosmopolitan during the late Wisconsin. Moderate environmental gradients of the equable late Wisconsin climates allowed integration of boreal species with resident species in the south.