Predation risk shapes thermal physiology of a predaceous damselfly, Enallagma vesperum (Odonata: Coenagrionidae)

Although warming temperatures affect insect population dynamics by increasing the rates of various biological processes, predation risk can also have strong effects on population dynamics via modified behavior and physiology of individuals. To predict how insect populations respond to climate change, thermal effects on behavior and physiology should thus be measured in the context of predation risk. We evaluated how temperature and predation risk affected growth rates of a predaceous damselfly, Enallagma vesperum (Odonata: Coenagrionidae). We measured consumption rates, assimilation efficiency, production efficiency, and growth rates of damselfly nymphs across five temperature levels crossed with the presence or absence of a fish predator. We then developed a process-based model to explain differences in growth rates. Our results indicated that predation risk shaped the thermal response of consumption rate, production efficiency, and growth rates. Assimilation efficiency was invariant with temperature but higher under predation risk. Growth rates decreased at the highest temperatures due to the inability of consumption rates to keep up with a higher energy demand. The decreased growth rates under predation risk were explained by the higher temperature sensitivities of consumption rate and metabolic rate. Thus, we demonstrated how differences in thermal sensitivities and predation risk reduced the predicted benefits of warmer temperatures on insect growth rates. Given the magnitude of thermal changes occurring across the globe and associated ecological changes such as invasive species, putting thermal physiology in a community context is required for adequately testing and predicting insect population response to climate change.