The effects of temperature and activity on intraspecific scaling of metabolic rates in a lungless salamander.

The scaling of metabolic rate with body mass holds substantial predictive power as many biological processes depend on energy. A significant body of theory has been developed based on the assumption that metabolic rate scales with body mass as a power function with an exponent of 0.75, and that this scaling relationship is independent of temperature. Here we test this hypothesis at the intraspecific level in a lungless salamander using data on both standard and maximal metabolic rates (SMR and MMR, respectively). We also address a recently proposed alternative explanation that predicts systematic variation in this mass-scaling exponent, the metabolic level boundaries hypothesis (MLB). Consistent with predictions of the metabolic theory of ecology the mass scaling of SMR and MMR were independent of temperature, however, we find evidence that the mass-scaling exponent for SMR and MMR differ significantly from 0.75. Further, our data do not provide strong support for MLB. Mass-scaling exponents for MMR generally exceed those for SMR, although these differences are rarely statistically significant.