Meeting Abstract

19.4  Jan. 5  Proceed with caution: invalidating tests of the cost-benefit model of thermoregulation with spatially-explicit movement simulations SEARS, Michael W.; Southern Illinois University msears@zoology.siu.edu

The Huey-Slatkin model of behavioral thermoregulation in lizards predicts that individuals should thermoregulate less effectively in costly environments. A recent test of this prediction (Blouin-Demers and Nadeau 2005) used published data of thermoregulatory indices for 22 lizard species, 4 snake species and one species of amphibian to suggest that this prediction is not upheld. Specifically, the test failed to show a positive correlation between an index of the accuracy of thermoregulation (d_b) and an index of thermal quality of available habitat (d_e). The authors then concluded that individuals can thermoregulate accurately regardless of the thermal quality of available habitat. One important cost that cannot be accounted for in such a test is the influence of explicit spatial configurations of operative temperatures in the environment. Using a constrained random walk simulation of animal movement that incorporates thermoregulatory decisions and thermal properties of individuals, I explored the spatial conditions under which such a test of the Huey-Slatkin model could be performed. Results of these simulations revealed that the true null model to be tested against cannot be known unless the spatially-explicit distribution of operative temperatures in the environment are specified. If the spatial configuration of operative temperatures is unknown (as with the test by Blouin-Demers and Nadeau), the consequence is that any potential slope for the relationship between the accuracy of thermoregulation and the thermal quality of available habitat cannot be distinguished from the expected null hypothesis. Therefore, it is suggested that future tests of the Huey-Slatkin model of thermoregulation should be performed among conspecific individuals under very specifically-defined spatial distributions of operative temperatures.