O’CONNOR, M. P.; Drexel University, Philadelphia, PA: Convective heat exchanges for terrestrial ectotherms near the ground.

For terrestrial ectotherms, thermal energy balances play a critical role in constraining physiology, behavior, and ecology. For many of those ectotherms, their heat balances can be approximated as a balance between radiative and convective heat exchanges. Previous studies have shown that nearby flow obstructions alter convective exchanges, but few studies have addressed the conditions under which such obstructions could be important. Because most heat budgets are estimated via biophysical methods (which assume no nearby obstructions) rather than measured, this constitutes a significant limitation on our ability to analyze the thermal ecology of animals. As a first step toward a conceptual understanding of this problem, I examined the conditions under which an omnipresent obstruction, the substrate, might affect estimates of convective heat exchange. A finite element model of both laminar air flows and heat exchanges near a hypothetical lizard and its substrate was used to examine the effects of wind speed, body and environmental temperatures, and proximity of the lizard to the substrate on convective heat exchanges. The distance between the lizard’s venter and the substrate affected the air flow pattern, regional heat exchanges (up- vs down-stream, ventral vs dorsal) and overall heat exchanges. As the venter-substrate distance decreased below 50% of torso diameter, areas of stalled flow and eddies developed, ventral air temperatures were strongly affected by substrate temperatures, and marked variation in regional heat exchanges developed. By extending these simulations to turbulent air flows and to other flow obstructions, we can develop a systematic understanding of the role of substrates in affecting heat balances of ectotherms.