PARENT SESSION
Symposium #29: Scaling the implications of organismal size across evolutionary time and ecological space: A synthesis of recent advances and insights..
Organized by: BJ Enquist, F Smith, and PA Marquet
Thursday, August 8. 1:00 PM to 3:45 PM. Crystal Ballroom, TCC.
Evidence from ordinal level patterns for multiple body mass optima in mammals.
Alroy, John*,1, Dayan, Tamar2, Hadly, Elizabeth3, 1 National Center for Ecological Analysis and Synthesis, Santa Barbara, CA2 Department of Zoology, Tel Aviv, Israel3 Department of Biological Sciences, Stanford, CA
ABSTRACT- A large body of literature has invoked microevolutionary, biogeographic, and allometric patterns to argue that mammals evolve toward an optimal body size of around 100 g. However, direct macroevolutionary trends based on the North American mammalian fossil record suggest a more complex pattern. We show that over the last 65 million years, different orders of mammals have evolved non-randomly toward different parts of the body mass spectrum. Although rodents do seem to be constrained to a narrow size spectrum centered on 100 g, both major groups of ungulates (Artiodactyla and Perissodactyla) have evolved non-randomly out of this size range, in accord with Cope's rule. At the other extreme, the Insectivora have been very narrowly constrained within a narrow size range, with their average size always being much less than 100 g. Finally, the Carnivora show yet another pattern, with larger carnivores tracking the ungulate size trend even while smaller lineages persisted. We present parametric tests of the idea that body sizes in each order evolve toward a distinct evolutionary attractor, as well as simulation results that show that major trends could not have been produced by an unconstrained random walk or by the evolution of all lineages toward a single attractor.
KEY WORDS: body mass, Mammalia, macroevolution, macroecology