Aggregate Effects of Multiple Predator Species on a Shared Prey

We evaluated the potential for emergent nonlinear effects of multiple predators on mortality of a shared prey species by conducting experiments in cages in an old field. We examined interactions among three spider predators, Pisaurina mira, Phidippus rimator, and Rabidosa rabida, and a grasshopper prey Melanoplus femurrubrum. The predators have disparate hunting behaviors and are located in different parts of the vegetation canopy used by the grasshoppers, suggesting the potential for nonlinear effects. We examined the effects of spider species singly and in all possible combinations using a substitutive design in each of two years. Multiple predator effects on grasshopper mortality were generally the average of the corresponding single-species effects, indicating that the species effects were largely substitutable. This result indicates that it is reasonable to aggregate these predator species into a single functional unit, despite their disparate individual effects on grasshopper prey, when modeling predator–prey interactions for this system.