Warming effects on population sizes and top–down control are dependent on temperature range

Rising global temperatures are expected to affect natural ecosystems, but predicting the consequences is challenging given the complexity of ecological communities. Natural communities are complex networks of interacting species, and temperature changes can thus influence species directly and indirectly via changes in their various interactions with other community members within and across trophic levels. While previous studies indicate both predation and competition can be temperature specific, we still have a poor understanding of how both interact along a thermal gradient. Additionally, temperature effects appear contradictory across studies, potentially because they are typically limited to few temperatures which cannot capture the expected non‐linear relationship with temperature. Here we examine the effects of temperature on a food‐web including one predator feeding on two competing prey species to tease apart its direct effects on populations, indirect effects on competition and predation, and their interactions. We experimentally manipulated the presence of a predator and competitor for both prey species. We then exposed the six species treatments to a temperature gradient from 10–31°C for ~3 prey generations and quantified prey population growth rate, probability of extinction and co‐persistence. We found that the probability of extinction, final population growth rate, and the potential for prey co‐persistence all demonstrated non‐linear, hump‐shaped responses to temperature. Predators increased the probability of extinction for both prey, and for one species this effect was strongest at intermediate temperatures. Predators also reduced the population size of both species. For one prey, this effect strengthened at warmer temperatures, causing prey populations to peak at lower temperatures with predators. Contrary to expectations, presence of a second prey had either no or a positive effect on prey persistence and population size, especially with predators, suggesting apparent mutualism. Overall, these results reveal temperature effects on ecological dynamics are often non‐linear and contingent on the community structure.