A Quantitative Assessment of the Range Shifts of Pleistocene Mammals

Much attention has been focused on the response of species to the climate change associated with the last deglaciation during the Pleistocene. Generally, species respond in an individualistic manner to climate change, and expand and contract their ranges independently; consequently, community composition is extremely variable over time. Although data are available to examine range shifts of species by mapping species ranges over time, most investigations to date have been qualitative. I quantitatively assessed changes in distributions of species to determine the degree to which species shifted their ranges independently over broad time scales. Data on Pleistocene mammal assemblages from the FAUNMAP database were divided into 4 time periods (Pre-Glacial, full Glacial, Post-Glacial, and Modern). Range shifts were characterized by change in the median position of the range from 1 time period to another, change in range size, and direction of the shift. The degree to which species were shifting their ranges independently of one another was evaluated by examining frequency distributions of each range shift parameter and comparing directions wherein species were shifting their range centroids. Many species are shifting their ranges in similar ways. Many species in each time transition change their range size very little. Species shift their range centroids, on average, between 1,200 and 1,400 km. Moreover, if the United States is divided into quadrats and the direction in which species with those quadrats shift their ranges is examined, it becomes clear that in each quadrat there are some directions that are favored over others. The majority of these distributions in the 2 oldest transitions differ from a uniform distribution. Therefore, the prediction that the individualistic responses of species to climate change should result in nonanalog communities likely is oversimplified.