Metabolic theory and elevational diversity of vertebrate ectotherms

The Metabolic Theory of Ecology (MTE) posits that the temperature-dependent kinetics of metabolism shape broad-scale patterns of biodiversity. Here we test whether the MTE accounts for patterns of diversity using 102 elevational diversity gradients of reptiles and amphibians. In particular, we examined the support for the two key predictions of the MTE: that the reciprocal of absolute temperature (1/kT) and diversity are linearly related and that the slope of that relationship is -0.65. We also tested two underlying assumptions of the MTE in cases with appropriate data, namely, that abundance is invariant among samples, and that behavioral thermoregulation influences the MTE predictions. We found that few studies supported the predictions of the MTE for the relationship between environmental temperature and elevational diversity using previous methods on individual gradients and using meta-analysis. The predominant relationship was curvilinear, and the slopes were steeper than predicted. In analyses of individual gradients, only 6% followed the MTE predictions in the strictest application, and 25% in the broadest. We found violations of the assumption of invariant abundances in all five test cases. All four herpetofaunal groups, regardless of behavioral thermoregulatory abilities, demonstrated poor fits to the MTE predictions. Even when arid gradients are removed, ameliorating the potential effects of water limitation, the MTE did not account for herpetofaunal elevational diversity. We conclude that an interplay of factors shapes elevational diversity gradients rather than the simple kinetics of biochemical reactions.