Physiological constraints to climate change: insights from the effects of temperature on standard metabolic rate in larval salamanders

1. Predictions of climate change susceptibility are critical in forming conservation policy. However, these predictions may not be generalized even among sister taxa. As such, the development of species-specific, quantitative predictors of sensitivity to thermal increases is vital to the proper allocation of conservation resources and priorities. Climatic variability hypotheses propose that species occupying larger geographic ranges should develop more robust physiological tolerances and be more resistant to temperature changes. 2. In this study, we investigated the effects of temperature variation on standard metabolic rates (SMR) of two species of larval salamanders, Eurycea cirrigera and E. wilderae, that share similar life histories but occupy distinct ranges of variable sizes. 3. To this end, SMR was determined using volume of oxygen consumption during closed-circuit respirometery trials conducted at 5 °C increments between 5 and 25 °C. 4. Standard metabolic rates were influenced by temperature, with a range of temperature-independent SMRs observed at those temperatures above each species’ laboratory-determined thermal preference. Concordant with their thermal preference (15.70 °C) and more narrow geographic range, E. wilderae exhibited a smaller scope of temperatures at which SMR was temperature-independent relative to E. cirrigera and showed depressed metabolic rates at the highest temperature tested. 5. Our results provide a mechanistic link for an ecological predictor of climate change susceptibility (i.e., range size) and indicate that physiological specialization that occurs in species of narrow geographic ranges may preclude adaptations to climate change.