Thermal environment and ecological interactions modulate the importance of evolution in response to warming

Understanding the interaction between evolutionary history, the current abiotic environment, and biotic interactions is critical for a more nuanced understanding of the response of communities to anthropogenic stressors. We leveraged a long term experiment manipulating temperature in mesocosms containing communities of phytoplankton and zooplankton to examine how evolution in response to long-term community warming affects consumer-resource dynamics at different temperatures. We showed that the evolution in response to warming depends on both the current thermal environment, as well as the presence of interactions between consumers and resources. We also demonstrated that evolution influences the outcomes of current ecological dynamics. For each consumer-resource pair, the effects of evolution were temperature-dependent, but both the effects and the temperature dependence itself additionally depended upon the identity of evolving species in each pair. Evolution resulted on a win-win situation for the first resource species: across all temperatures, this resource was more fit and the consumer was less successful, with fitness gains peaking at intermediate temperatures. For this resource species our results supported the "hotter is better" hypothesis, especially at moderate or intermediate temperatures, while "hotter is worse" for the consumer. In the second species pair, patterns were more complex. Warm-origin populations of both the second resource and the consumer generally failed to show improved fitness. Overall, our results show that evolution altered resource and consumer fitness, but these effects were dependent on the current combination of abiotic and biotic conditions.