A meta-analysis on the role of functional complementarity and intraguild predation on biological control

Abstract: Herbivore populations are regulated by multiple natural enemies, and combining
predators (“predator cocktails”) can improve pest suppression compared to the use of a single
species. However, their effectiveness depends on the balance between functional
complementarity and antagonistic interactions, such as intraguild predation (IGP), where
predators consume one another while sharing prey. Although widely studied, these mechanisms are often treated separately, and an integrative synthesis is still lacking. Here, I present a metaanalysis examining how phylogenetic diversity, functional diversity, and differences in predator kill rates jointly shape top-down control in two-predator, one-prey systems. We compiled data comparing single and paired-predator treatments across laboratory, greenhouse, and field settings. Predator cocktail performance was assessed relative to single predators, while trait differences (a measure of predator complementarity) and antagonism were quantified using functional trait differences, phylogenetic distances, and variation in predator efficacy. Our results show that predator cocktail effects vary across ecosystems and depend on interactions among phylogeny, traits, and efficacy, with differences in predator effectiveness emerging as a key factor. Overall, these findings highlight the need to balance predator traits and efficacy to enhance complementarity and reduce intraguild predation, improving biological control strategies.