Predator diversity enhances vector suppression: potential implications for pathogen prevalence

Studies of vector-borne disease dynamics have addressed the consequences of diversity loss for disease prevalence by focusing on diversity in the context of the host-vector-pathogen relationship, while the role of diversity at higher trophic levels has been largely neglected. However organisms at higher trophic levels, such as predators, may indirectly influence disease dynamics by reducing populations of pathogen vectors. We evaluated the impact of altered predator diversity on the abundance of the Bird cherry-oat aphid (Rhopalosiphum padi), a vector of barley yellow dwarf virus in wheat, by creating predator assemblages that varied in both the number and identity of species present. When we compared the effectiveness of predator assemblages consisting of a single predator species to that of assemblages with two or four predator species, we found that on average a diverse group of predators reduced vector abundance more so than single predator species. However, closer inspection revealed that this apparent benefit of diversity was actually driven by the presence of one particularly efficient predator species. Diverse predator assemblages were only more effective at vector suppression because they were statistically more likely to contain the most efficient species than treatments where only a single species was present. Therefore, we conclude that it is the identity of species in the predator assemblage, rather than diversity per se, that determines the size of the vector population, which may ultimately impact disease prevalence.