179-5 The evolution and distribution of species body size

See more from this Division: General Discipline Sessions
See more from this Session: Paleontology I - Macroevolution, Diversity, and Biogeography

Monday, 6 October 2008: 9:00 AM
George R. Brown Convention Center, 351CF

Aaron Clauset, Santa Fe Institute, Santa Fe, NM and Doug Erwin, Dept of Paleobiology, MRC-121, Smithsonian Institution, Washington, DC
Abstract:
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.

See more from this Division: General Discipline Sessions
See more from this Session: Paleontology I - Macroevolution, Diversity, and Biogeography