The importance of intraguild predation in predicting emergent multiple predator effects

Prey typically coexist with multiple predator species, each of which presents a predation risk related to its habitat domain and foraging mode. These predator characteristics can be used to predict how the risk from multiple predators will combine to create emergent multiple predator effects for shared prey. Interactions between predators, particularly intraguild predation, can strongly alter prey suppression, though the importance of intraguild predation in multiple predator effects has not been explicitly explored. Furthermore, the vast majority of studies on multiple predator effects has focused on shared prey that are herbivorous, thus experiments focused on mesopredators are needed to evaluate the generality of conclusions made about multiple predator effects. We used a suite of carnivorous arthropods to test a predictive framework of multiple predator effects and to evaluate the role of intraguild predation in shaping these effects. We allowed the wolf spiders Pardosa milvina, Tigrosa helluo, and Rabidosa rabida and the ground beetle Scarites quadriceps to interact and recorded the outcome of all predatory events. We used two tests of multiple predator effects to determine whether predators created risk enhancement, risk reduction, or were substitutable. We found that the occurrence of intraguild predation decreased the overall risk to prey, causing observed multiple predator effects to deviate from predictions. Additionally, we highlight the importance of considering predator identity, as predators were capable of increasing, decreasing, or not altering the success of their competitors. Our study demonstrates that intraguild predation is a critical factor in determining how the risk from multiple predators will combine to affect their prey.