Changes in global temperature can have important consequences for ecological communities by altering the metabolic rates of constituent species. Temperature-mediated changes in metabolic rates are especially important for consumer-resource interactions such as predation, because predation increases with predator metabolic demands. However, warming may also decrease predation by accelerating prey developmental rates toward size or stage refuges, for example, hastening ontogenetic niche shifts. Therefore, the effects of warming on the strength of predator-prey interactions will depend on the relative impact of temperature on predation rates and prey developmental rates. To test this hypothesis, we quantified the temperature-dependent functional response of a nymphal dragonfly predator (Pantala hymenaea) on larval mosquito prey (Culex spp.). We then coupled our results with literature estimates of temperature-dependent mosquito development and mortality and built a model to predict the strength of predation across a thermal gradient. Lastly, we related our findings to field estimates of temperature variation and dragonfly and mosquito abundance in rock pools in the James River (Richmond, VA) where these species are common.
Results/Conclusions
In a laboratory experiment, we quantified predator functional response curves at temperatures ranging from 12°C to 42°C. Nymphal P. hymenaea predation on larval Culex spp. exhibited a type-II functional response, saturating at higher prey densities. Attack rates were best described via a unimodal function of increasing temperature, peaking at 32°C. Surprisingly, differences in overall predation rates across temperatures were small, which suggest P. hymenaea nymphs may be thermal generalists. This finding matches their ubiquitous distribution across the thermally variable James River rock pools, as well as other aquatic habitats. Model estimates of the impact of temperature on predation of Culex spp. suggest that as temperature increases, predation strength decreases. This is because the benefits of increased Culex spp. developmental rates outweigh the negative effects of comparatively mild increases in P. hymenaea feeding rates. Our results suggest that when prey developmental rates are relatively more sensitive to temperature than predator attack rates, increases in temperature may weaken instead of strengthen predation by shortening the duration of prey exposure to predators.