Temperature has a unimodal effect on the functional response of wolf spiders

The response of biotic interactions to changes in temperature will play a large role in determining the impact of climate change on ecological communities. In particular, how warming alters predator-prey interactions will influence population stability, food web connectivity, and the movement of energy across trophic levels. The functional response relates predator foraging rates to prey availability, and it is often predicted to increase monotonically with temperature, at least within the limits of predator function. However, some studies suggest that functional responses peak and then decline, and such a difference has critical implications for the effect of warming on ecological communities. Here we investigate the effect of temperature on the functional response of wolf spiders (Schizocosa saltatrix) foraging on midges. Our results clearly support a unimodal response of the functional response, with peak foraging occurring at normal daytime temperatures for the area. Thus, daytime active spiders might experience a decline in foraging with warming, while night active spiders might experience an increase in foraging. Together with previous work, our study strongly suggests that the widespread assumption of a monotonic increase in foraging with warming is not warranted.