Reduced predator avoidance behavior and higher exposure to thermal stress for prey during heat wave events

Heat wave events threaten natural communities by causing mass mortalities and altering species interactions. Some organisms can use behavioral thermoregulation to avoid extreme temperatures, which may buffer them against rising incidents of heat events. While behavioral thermoregulation is effective at avoiding stressful temperatures, less is known about how it can alter other adaptive behaviors like predator avoidance. In this study, we used laboratory and outdoor mesocosm experiments to understand how behavioral thermoregulation is impacted by the presence of local predators during heat wave events, by exposing intertidal marsh periwinkles (Littoraria irrorata) to simulated heat waves and cues from blue crabs (Callinectes sapidus). We measured snail climbing height and body temperatures to disentangle snail decisions to thermoregulate or avoid predators under increasing heat stress. Our results indicate that antipredator behavior can be severely reduced in heat wave simulations, in temperatures well below the snail's upper thermal limits. Snails chose lower climbing heights that allowed them to avoid stressful temperatures but brought them within reach of subtidal predators. Thus, while heat waves may not directly kill snails because they can behaviorally thermoregulate, reduction in antipredator response can increase their encounters with subtidal predators. Additionally, when snails maintained antipredator climbing behavior in lower intensity heat wave simulations, snails occupied hotter microclimates and had higher body temperatures, indicating predator avoidance increases the temperatures snails experience. Local predator presence can increase the exposure of prey species to temperature stress during heat events, and these events can decrease the size and number of tolerable microhabitats for mobile ectotherms.