A Stochastic Dual-Limit Hypothesis for Behavioral Thermoregulation in Lizards

Abstract

Heath has proposed that thermoregulatory behavior of lizards is controlled by maximum and minimum limit temperatures (high and low setpoints) separated by a nonthermoregulatory zone. On precursory examination this hypothesis seems incompatible with the unimodal distribution of body temperatures of lizards in the field and in continuous thermal gradient experiments. Evidence from two-temperature selection experiments indicates that the high and low limit temperatures are stochastically distributed. Based on this observation, we have formulated a stochastic mathematical model of the system which predicts the distribution of body temperatures of lizards confined in a temperature gradient. According to the model, an increase in the variance of the limit temperatures results in decrease in the variance of the unimodel distribution of body temperatures in a continuous gradient. As the variance of the lower limit increases relative to that of the upper limit, the model predicts a negatively skewed distribution of body temperatures, a common observation in continuous gradient experiments.