Abstract
Predators can help determine the density and diversity of prey populations. Predators can reduce densities of prey, increase diversity of prey species, lower densities of other predators, and cause changes in the overall biomass production of a community. Schmitz (2007) developed a framework to test multi-predator effects, which included two predictions based on the predators’ habitat and hunting mode. The first prediction is that increasing predator pressure causes a risk enhancing effect; multiple predators can be more efficient at removing prey and lowering overall prey densities. The second prediction is that competition among multiple predators develop a risk-reducing effect on prey; predators can interfere with one another by competition or intraguild predation, thus lowering their prey capture abilities. Even though there are many predator-prey studies, few have been focused in seasonal wetlands. The purpose of this study was to evaluate multiple predator effects on invertebrate community structure. I predicted that predators in vernal pools would have a risk-enhancing effect, resulting in the reduction of prey densities and increasing overall diversity. To test this hypothesis, I used two different species of predators, backswimmers (Family Notonectidae) and damselfly nymphs (Order Odonata). The experimental mesocosm study consisted of nine treatments arranged in a factorial design. Density treatments consisted of three and six predators of the same species; diversity treatments consisted of equal numbers of Notonectidae and Odonata, as well as double density of predator of either species. I found that treatments containing Notonectidae had a negative effect on prey density, while treatments containing equal numbers of predators had a positive effect on prey density, and predator treatment did not have an effect on prey diversity. Communities were more likely to be similar within each treatment and not between treatments. I conclude that a risk-enhancing effect can occur when there are high densities of Notonectidae, additionally, the results suggest that when two different predator species are present in equal densities they may interfere with one another generating a risk-reduction effect on the prey community.