Thermal sensitivity and the role of behavior in driving an intertidal predator-prey interaction

Environmental stress models (ESM) provide a useful framework to study the direct and indirect ecological drivers of community diversity and resilience. ESMs make predictions about the relative importance of structuring processes (e.g., predation) based on the relative stress suffered by consumers and prey. Their practical application, i.e., determining the conditions under which consumers and prey performance is more negatively affected, has been limited because the roles of behavior and physiology are not usually considered. We examined the role of thermal sensitivity and behavior on the thermal performance of the rocky intertidal predator Pisaster ochraceus and its main prey Mytilus californianus. We propose a novel framework that merges thermal performance curves (TPC) with observations of microhabitat use to provide a realistic perspective of the relative physiological conditions of predator and prey. First, by deriving aquatic and aerial TPCs for both species and from two sites, we found differences in parameter values that in some cases correspond to the individuals' origins. Second, we calculated realized thermal performance in the field by combining TPCs with body temperatures recorded with biomimetic sensors. Notably, thermal performance of Pisaster was higher than that for Mytilus (i.e., prey-stress model), contrary to previous expectations based on caging experiments. Third, these estimates of thermal performance corresponded loosely with a measured indicator of overall physiological condition (body mass index, BMI) and a marker for extreme thermal stress (heat-shock proteins 70 kDa), suggesting that environmental drivers other than temperature, such as food supply, must be considered. We found no evidence that Pisaster movement significantly influences thermal performance under typical conditions, suggesting instead that its preference for sheltered microhabitats provides a mechanism for avoiding exposure to extreme environmental conditions. Through the application of TPCs and ESMs, this study provides a unique perspective on the importance of physiology and behavior in driving the sensitivity of species interactions to environmental change. Crucially, this framework allowed clarifying that this system behaves as a prey-instead of consumer-stress model, which may also apply to many other ectotherm -species interactions.