Interactive effects of predation and competition on dispersal rates

Background/Question/Methods

Dispersal has important consequences for the ecology and evolution of populations. For example, dispersal affects metapopulation persistence, demographic and genetic structure of populations, and local adaptation. Given the influence of dispersal on biological processes, it is important to understand the factors that cause dispersal. Previous studies have shown that dispersal may be induced by a variety of ecological stressors. Most of these experiments have focused on the effects of just one stressor; however, individuals likely experience combinations of multiple stressors simultaneously and must incorporate cues from several sources in order to accurately assess habitat quality and weigh the costs and benefits of dispersing. If these multiple ecological stressors have interactive rather than additive effects, estimates of effect sizes from single-stressor experiments may be misleading. In this study, we asked whether interactive effects between two common ecological stressors, predation risk and competition, influence dispersal dynamics. We tested this question in pond mesocosms using backswimmers (Notonecta undulata), a flight-capable aquatic insect. We performed a factorial experiment in which we crossed predation risk with competition strength. We measured emigration rates out of the experimental mesocosms.

Results/Conclusions

We found that dispersal rates depended on both predation risk and competition, as well as their interactive effects. These results suggest that precise estimates of the effects of predation risk or competition on dispersal require inclusion of their interactive effects. More generally, multi-stressor experiments may reveal a more complete picture of dispersal dynamics across a range of ecological conditions.