DUNHAM, A.E.; O’CONNOR, M.P.; Univ. of Pennsylvania; Drexel Univ.: Connecting physiology to demography and life history in ectotherms

A fundamental assumption in ecology is that an animal�s habitat and physiology interact to limit the demography and distribution of a species. But physiological effects on population biology in the field have rarely been demonstrated. The paucity of examples is due to: 1) the complexity of each physiological effect on demography and interactions among multiple physiological effects, and 2) inability of analytic techniques to integrate complex effects into useful predictions. Physiological, individual based models can integrate such complex physiological systems into useful ecological predictions. We propose a framework for applying such models to animal populations and use that framework to evaluate predictions about demography in a model organism, Sceloporus merriami. The framework assumes that demography is limited primarily by critical resources (water and energy). Resource acquisition is modeled as depending on: 1) resource availability, 2) physiologically (e.g., thermally) limited activity (for resource harvesting), 3) physiologically limited processing of harvested resources, 4) resource expenditures (e.g., metabolism and water loss), and 5) seasonal / annual variation in habitat and physiology. We assume that several types of habitat patches available for use at any time (including a refugium), and animals choose the habitat that optimizes resource gain while avoiding intolerable conditions. We model all exchanges (heat, water, energy) as mechanistically as possible under the constraint that typical physiological data must be applicable to the model. Resource acquisition is modeled over one or more activity seasons or years. We apply the model to the ecology of several populations of Sceloporus merriami in a system where conceptual models have done a poor job of predicting the ecology of the animals.