LATE PLEISTOCENE MAMMALS: BODY SIZE AND LOCAL COMMUNITY STRUCTURE

Body size distributions of modern mammals differ with spatial scale; continental faunas are right-skewed and highly modal, whereas local faunas are essentially uniform. Modal-sized species turn over more rapidly across space, while larger and smaller species occur repeatedly in different local faunas. Such patterns imply that body size mediated competition plays an important role in the structuring of local communities. Because there were considerable changes in the distributions of species, both terrestrial and marine, in response to the last glaciation cycle, the Late Pleistocene of North America is an ideal system with which to examine the role of body size in the structuring of local communities through time. I examined the body size distributions of local assemblages of mammals across the last 40000 yrs. Faunal lists for localities were taken from FAUNMAP along with the age and geographic position of the locality. Body size data were taken from a compilation by Smith et al., 2003. The distributions were evaluated for biases with respect to sampling and degree of time averaging. Localities with less than 20 species tended to cover a smaller range of body sizes and were eliminated from analyses. Data for modern localities were taken from Brown and Nicoletto (1991). Body size distributions of Late Pleistocene localities were compared to continental distributions and uniform distributions using Kolmorgorov-Smirnov two-sample tests. Because of the extinction of megafauna 10000 yra, the continental distribution used for comparison differed depending upon the age of the locality. A majority of the localities were significantly different from their continental distribution, and were not different from a uniform distribution. Given the considerable turnover in local community composition during the last glaciation, the similarity between the body size distributions of Late Pleistocene communities and modern communities implies that body size plays a key role in local community structure.