Climate warming is predicted to increase surface water temperatures in the Midwestern United States by as much as 5°C over the next century. Such rises in temperature will have direct effects on species’ physiology, and indirect effects on species interactions that may scale up to alter populations and food webs. In particular, warming is expected to increase predator-prey interaction strengths of ectothermic organisms by increasing their metabolism, movement, and the frequency of encounters between predators and prey. However, the degree to which warming will influence predator-prey interactions will likely depend on the predator’s foraging strategy, predator and prey movement, and thermal performance. Warming may disproportionately increase prey consumption rates of active predators that can move more rapidly at high temperatures to increase their encounters with prey; whereas sit-and- wait predators may not increase prey consumption as much with warming, because prey movements determine their encounter rates. We used laboratory experiments to quantify the effects of temperature on predator-prey interactions of freshwater insects with different foraging strategies: active predators, Notonecta backswimmer larvae, and sit-and- wait predators, Enallagma damselfly larvae, interacting with active prey Daphnia zooplankton. We quantified predator-prey interaction strengths as the predator’s functional response to prey across a temperature range of 10-35°C. We analyzed video recordings of these experiments to quantify how predator-prey movement and foraging behaviors of prey encounters and attack rates vary with temperature.
Results/Conclusions
We demonstrate that predator-prey interaction strengths increase with warming for both the active and sit-and- wait predator. However, the active predator increases its encounter and attack rates more with warming compared to the sit-and- wait predator. Predator-prey movement also increases with temperature, but the form of the temperature response differs between active and sit-and- wait predators, and explains why attack rates increased more with warming for the active predator. Surprisingly, we found that predator consumption strategy also influences interaction strengths, whereby the sit-and-wait predator increases its prey handling rate more with warming than the active predator, due to its ability to more rapidly engulf prey. Our research demonstrates that foraging and consumption strategies influence predator-prey interactions with rising temperatures, and should be accounted for when forecasting how climate warming will alter food webs. Further study of these traits may improve predictions of which species will be “winners and losers” of climate change.