Background/Question/Methods
Water temperatures are forecasted to increase by up to 5°C in Midwestern aquatic ecosystems over the next century. Rising temperatures have direct metabolic effects on aquatic species, and indirect effects on their behaviors and trophic interactions. Current theory predicts that as temperatures rise, predator attack rates will increase as a function of both increasing predator and prey movement rates. We studied how interactions between a predatory freshwater insect, the backswimmer Notonecta undulata and their prey species, the water flea Daphnia pulex, changed with rising temperatures. We examined whether the relationship between attack rate and temperature was explained by increasing predator and prey movement rates with warming. We hypothesized that Daphnia and Notonecta velocities would change significantly across a 10 - 35°C temperature range, with peak velocities at an intermediate temperature. We predicted that these changes in predator-prey movement would alter attack rates and encounters across the temperature range. These hypotheses were tested by collecting Daphnia and Notonecta from ponds at Lux Arbor Reserve, Southwestern Michigan, acclimating them to a range of temperatures, and video recording their interactions and movements. We analyzed video data for velocity, movement frequencies, encounters, and attack rates.
Results/Conclusions
We found significant changes in Daphnia velocity across the temperature range. Daphnia velocity increased exponentially between 10 and 35°C, beyond which temperatures were lethal. Notonecta increased its attack and encounter rates between 10 and 35°C, and velocity and movement frequency up to 30°C. Understanding how predation rates will change with climate warming is crucial towards predicting shifts in aquatic community structure and function over the next century, along with promoting more effective management of freshwater ecosystems.