Alternative extraguild prey modifies focal extraguild prey consumption and parasitism but not intraguild predation intensity

Intraguild predation (IGP) refers to the predation of species that use similar resources and are, therefore, potential competitors. The consuming predator is known as the intraguild predator (IG-predator) and the predator or parasitoid being consumed as the intraguild prey (IG-prey). Prey belonging to another guild are known as extraguild prey (EG-prey). Within a single prey-predator framework, the presence of an alternative prey can reduce the predation rate of a focal prey. However, such an effect has not been studied in an IGP framework. In addition, most studies conducted to analyze IGP intensity (i.e., the level of consumption of the IG-prey) have focused on the influence of a single focal EG-prey but not on the effect of an alternative EG-prey. Therefore, in an IGP framework, we aimed to assess how the presence of an alternative EG-prey could affect the predation and parasitism rates of a focal EG-prey, as well as IGP intensity. On the basis of intrinsic characteristics of the IGpredator and current literature, we hypothesized that the presence of the alternative EG-prey would reduce predation and parasitism of the focal EG-prey as well as IGP intensity. Our results showed that, as expected, the presence of an alternative EG-prey reduces the predation rate of the focal EG-prey when both the IG-predator and the IG-prey are released concomitantly, but not when the IG-predator is released sequentially. In addition, contrary to our expectations, the presence of an alternative EG-prey did not reduce the intensity of IGP, indicating that besides intrinsic characteristics of the IG-predators, other factors may be important mediators of IGP intensity. Potential implications of these findings are discussed under a biological control perspective.