2008 Joint Meeting of The Geological Society of America, Soil Science Society of America, American Society of Agronomy, Crop Science Society of America, Gulf Coast Association of Geological Societies with the Gulf Coast Section of SEPM

Paper No. 5
Presentation Time: 9:00 AM

The Evolution and Distribution of Species Body Size

CLAUSET, Aaron, Santa Fe Institute, 1399 Hyde Park Rd, Santa Fe, NM 87501 and ERWIN, Doug, Dept of Paleobiology, MRC-121, Smithsonian Institution, PO Box 37012, Washington, DC 20013-7012, aaronc@santafe.edu

The distribution of species body size within taxonomic groups exhibits a heavy right-tail extending many orders of magnitude, with most species being significantly larger than the smallest species. We present a simple model of cladogenetic diffusion over evolutionary time that omits explicit mechanisms for inter-specific competition and other microevolutionary processes yet fully explains the shape of this distribution. We estimate the model's parameters from fossil data on terrestrial mammals since the K/T boundary and find that it robustly reproduces the distribution of 4002 mammal species from the late Quarternary. The observed fit suggests that the asymmetric distribution arises from a fundamental tradeoff between the short-term selective advantages (Cope's rule) and long-term selective risks of increased species body size, in the presence of a taxon-specific lower limit on body size.