Geographic variability in North American mammal community richness during the terminal Pleistocene

In North America during the terminal Pleistocene (ca 15,000–10,000BP), patterns of geographical variability in mammal community richness differed from those observed here today. This paper presents analyses of paleontological and archaeological faunal data from throughout the continental US, and these analyses control for factors that might confound paleontological measurement of past community richness. These analyses suggest that, in contrast to the present, and regardless of whether richness is measured at the local or the regional scale, terminal Pleistocene terrestrial mammal communities in the eastern portion of mid-latitude North America were richer than, or at least as rich as, communities in the west. In addition, the richness of large herbivores declined from south to north, in contrast to the current situation, in which large mammal richness increases with latitude across North America. The reversal in the north-south gradient in large mammal richness suggests that the richness of such taxa was determined primarily by available environmental energy during the terminal Pleistocene, whereas the modern pattern might be, at least in part, a result of the extinctions that occurred here near the end of the Pleistocene. The reversal in the east-west gradient indicates that two variables that have been proposed to be responsible for the gradient observed today—mean elevation and habitat heterogeneity associated with variability in elevation—could not have driven differences in richness between the east and the west during the terminal Pleistocene. Rather, these differences were likely the result of differences in energy and/or differences in habitat heterogeneity that were not related to elevational variability. r 2004 Elsevier Ltd. All rights reserved.