PARENT SESSION
Symposium 23: Body Size, Biophysics and Biological Stoichiometry: From Individual Function to Ecosystem Structure
Organized by: J Sabo and B Enquist
Friday, August 8. 8:30 AM to 12:00 PM, SITCC Chatham Ballroom B.

Effects of size and temperature on population growth.

Savage, Van^{*,1, 2}, Gillooly, James³, Brown, James^{1, 3}, West, Geoffrey^{1, 2}, Charnov, Eric³, ¹ Santa Fe Institute, Santa Fe, NM, USA² Los Alamos National Laboratory, Los Alamos, NM, USA³ University of New Mexico, Albuquerque, NM, USA

ABSTRACT- Since the time of Malthus, population growth has been recognized as providing a critical link between the performance of individual organisms and the ecology and evolution of species. We present a theory that shows how the intrinsic rate of exponential population growth, r_max, and carrying capacity, K, depend on individual metabolic rate and resource supply rate. To do this we construct equations for the metabolic rates of entire populations by summing over individuals, and then combine these population-level equations with Malthusian growth. These individual-level and population-level processes are inextricably linked because metabolism sets both the demand for environmental resources and the resource allocation by individuals to survival, growth, and reproduction. We use this theory to explain how and why r_max scales with body size and temperature. Data for algae, protists, insects, zooplankton, fishes, and mammals confirm these predicted scalings. The metabolic flux of energy and materials also dictates that the carrying capacity for populations increases with increasing body size and temperature. We then extend the theory to argue that most of the variation in mortality and fecundity rates is also determined by body mass and temperature. These predictions are supported by data for instantaneous mortality rates of marine fishes in the field. This theory links rates of metabolism and resource use of individuals to life history attributes and population dynamics for a broad assortment of organisms, from unicells to mammals.

Key words: temperature, allometric scaling, r_max, carrying capacity