Meeting Abstract
All biological activities depend on metabolic energy, and thus understanding why metabolic rates vary across species is of fundamental importance in understanding how animals work. For mammals, it is generally understood that metabolic rates are elevated in marine species despite considerable taxonomic and ecological diversity. There are two prevailing, non-mutually exclusive hypotheses to explain this phenomenon: as an adaptation for aquatic endothermy and/or as a consequence of the high costs of carnivory. In this study, we used a phylogenetic comparative approach to examine the effects of environment (aquatic vs. terrestrial) and diet (carnivory vs. non-carnivory) on the scaling patterns of metabolic rates in mammals. To test for differences between groups, we performed phylogenetic generalized least-squares regressions and analysis of covariance on the resting and field metabolic rates of 537 and 90 eutherian mammal species, respectively. We also performed ancestral state reconstructions to map the evolution of metabolic rates across all mammals. We show that while resting metabolism is elevated in some marine taxa, it is not unique to the aquatic environment nor is it a shared characteristic of all marine species. Our analyses also indicate that the field metabolic rates of marine mammals are comparable to those of other mammals both on average as well as in their variability. Additionally, we found that the field metabolic rates of marine mammals are indistinguishable from those of terrestrial carnivorans. Together, these results suggest that marine mammals are not exceptional in their metabolic energy needs, are metabolically diverse, and that carnivory may be more important than environment as a predictor of metabolic adaptations in aquatic mammals.
