Meeting Abstract

19.4  Saturday, Jan. 4 11:00  Macroevolutionary relationships between size and diet in mammals. PRICE, S. A.*; HOPKINS, S.S.; Univ. of California, Davis; Univ. of Oregon saprice@ucdavis.edu

Living mammals exhibit remarkable variability in body mass, spanning eight orders of magnitude from the bumblebee bat (~1.3g) to the blue whale (~160 tonnes). Due to the high energy demands of homeothermic endothermy, diet and mass are expected to be tightly linked in mammals: as size increases dietary quality decreases. The observation that mammalian basal metabolic rate usually scales to 3/4 power of mass (Kleiber’s law) explains why larger mammals are able to subsist on lower quality diets, as their energy requirements are lower per unit of mass. This predicts, amongst other things, that herbivores should be larger than carnivores. Using data from 1,300 mammals we tested for different size optima among different diets with generalized Ornstein-Uhlenbeck models. Across all mammals the best-fitting model was one that allowed both the optima and the rate of evolution to vary with diet. The model-averaged optima reveal that in general herbivorous mammals are much larger than carnivores, with an optima of 30kg and 4.5kg respectively. However, there is little difference between the optima for omnivores (5kg) and carnivores, suggesting perhaps that carnivorous and omnivorous mammals have similar overall diet qualities. Our results confirm that, despite the very different constraints on mass in terrestrial, volant and aquatic species, herbivory is linked to larger size across all mammals.