Why Short-Term Experiments May Not Allow Long-Term Predictions about Intraguild Predation

Equilibrium models are increasingly employed in applied ecology, but often because of experimental logistics, only short-term laboratory experiments are performed. Here, we use simple models to examine the management relevance of this disconnection between theory and experiments in communities with intraguild predation (IGP). Equilibrium theory shows that IGP can promote coexistence of competitors on a shared resource. However, adding the intraguild predator can result in higher resource densities than in a system with the intraguild prey alone with its resource. This has important management implications when the shared resource is a pest species whose population is controlled by natural enemies. Our models demonstrate why short-term experiments and studies ignoring alternate resources may bear no relationship to a system at equilibrium. Short-term experiments quantifying only attack rates can predict a broad range of outcomes. By ignoring conversion efficiency, consumer longevity, and immigration, short-term studies may, for example, cause erroneous decisions about the introduction of natural enemies in biological control. Thus, attack rates, conversion efficiencies, and immigration rates must all be quantified for a thorough, long-term understanding of IGP in field systems.