Temperature triggers a non‐linear response in resource–consumer interaction strength

Although temperature is recognized as a major determinant of many ecological processes, it is still not clear whether temperature increase caused by climate change will strengthen or weaken species interactions. One hypothesis is that interactions will respond non‐monotonically to temperature because thermal performance curves, which determine the strength of these interactions, are also non‐monotonic. To evaluate this hypothesis, we developed a temperature‐dependent consumer–resource model and tested predictions from this model in large freshwater mesocosms populated with green algae (Chlorella vulgaris) and herbivorous zooplankton (Daphnia magna). We found both in the model simulations and empirical investigations that the suppressive effect of the consumer depended non‐monotonically on the temperature. As predicted by the model, Daphnia suppressed the algal maximum per capita growth rate at the temperature that maximized algal growth rate but had little effect on resource growth at either lower or higher temperatures. This finding could help explain why effects of temperature variation on species interaction are variable in the literature and suggests that predicting the effects of temperature on the strength of food web interactions requires knowledge of the thermal performance curves for multiple traits, for multiple species and over a range of temperatures. Temperature is perhaps the most widely recognized environmental factor driving ecological processes today. Change in temperature experienced by organisms because of climate change has been documented to trigger behavioral responses, shifts in geographic distribution and phenological mismatches between consumers and resources (Hughes 2000, Parmesan 2006, Hansen et al. 2010). In addition, temperature is expected to affect the way species interact via changes in organismal physiology (Dell et al. 2011, 2014, Schaum 2017). For example, the feeding rate of two species of Daphnia under controlled conditions increased with initial changes in temperature, making Daphnia a more effective grazer (West and Post 2016). However, at higher levels of temperature, Daphnia feeding rate dropped sharply, compromising grazing capacity, whereas algal growth rate remained high. These differences in response to temperature variation between resource and consumer could have cascading effects on food web structure, ecosystem function, and biodiversity given that consumer–resource dynamics control the flow of energy between trophic levels (O'Connor et al. 2009, Gilbert 2014, Osmond et al. 2017). Thus, it is essential