Differences in thermal responses of feeding rates can reshuffle predator hierarchies under warming

Background/Question/Methods

Most resources are subject to consumption from multiple consumer species. Consumers generally show a natural hierarchy of relative consumption rates, with resource communities facing greater pressure from some consumers than others. However, feeding rates are strongly dependent on the temperatures individuals experience. Despite recent progress in documenting these relationships for individual species, it remains unclear how warming affects the hierarchies of consumers within a local community. Species should be adapted to their local temperature regimes, which might suggest a parallel shift in feeding rates across consumers and thus preservation of their hierarchies when the system warms. However, if differences in traits (e.g. physiology or ecology) between sympatric species play a significant role in shaping how feeding rates scale with temperature, warming may reshuffle predator hierarchies. Here we compare feeding rate thermal responses of six aquatic insect predators feeding on the same planktonic prey. Predators were collected from one pond in Northeast Texas, housed in 500ml water heated to temperatures from 8 – 36°C for 24 hours, then allowed to feed on 100 adult Daphnia pulex for two hours. The numbers of surviving prey were counted, and the numbers eaten were estimated after accounting for background mortality.

Results/Conclusions

Overall, we found differences in optimal temperatures and thermal sensitivities led to a reshuffling of the per capita feeding rate hierarchies among the predators. Of the six species tested, only one demonstrated the expected hump-shaped response of feeding rate to temperature within the range tested, while feeding rates of the other five species increased monotonically. Additional experiments indicated the lethal temperatures for each predator were greater than the maximum temperature at which prey could survive, though for some it was only greater by 2-3°C. Interestingly, this suggests the decline in predation rates at higher temperatures predicted by past studies may not always be relevant in natural system. Furthermore, we found feeding rates of consumers differed in sensitivity to changes in temperature. Consequently, increasing feeding rates with rising temperatures in one species can be offset by decreasing feeding rates in another. These results indicate a complex relationship between total consumption and temperature at the community level. They also suggest climate warming could restructure ecological networks, with major implications for the functioning of ecosystems and evolution of predator and prey traits.