Meeting Abstract
Every organism must thermoregulate to maximize its performance, but competing organisms limit access to preferred microclimates. Such competition creates hierarchies in which dominant individuals have more access to thermal resources than subordinate individuals, thus creating disproportionate costs of thermoregulation. To assess the costs of competition, we measured the body temperatures, activity levels, and hormone concentrations of male lizards (Sceloporus jarrovi) in a thermal arena, when alone and when paired with a smaller or larger lizard. Competition caused large males to use the heat source more often, resulting in body temperatures above the preferred temperature range. Conversely, small males spent less time near the heat source and permitted body temperatures to regularly fall below their preferred temperature range. Competition caused both large and small males to circulate more corticosterone, although this effect was more pronounced in small males. Similarly, competition caused large males to circulate more testosterone, while small males circulated less testosterone. Both dominant and subordinate males paid costs of competition for thermal resources, including poorer thermoregulatory performance and greater physiological stress. Thus, competition for thermal resources should feature more prominently in ecological and evolutionary models of thermoregulation.
