Predator diversity affects vector abundance and movement: Conflicting implications for pathogen prevalence?

Background/Question/Methods

The consequences of diversity loss for vector-borne disease dynamics have been well-studied in the context of host-vector-pathogen relationships.  However the role of diversity at higher trophic levels has been largely neglected with respect to these interactions. Predators, and furthermore predator diversity, may indirectly influence the occurrence of disease by directly altering the abundance and/or behavior of vectors that are responsible for pathogen transmission. Our goal was to determine if altered predator diversity impacts vector abundance or movement, and if so, whether these effects cascade down to influence the prevalence of a pathogen in a host plant community.

Results/Conclusions

To address the role of predator diversity in vector-borne disease dynamics, we evaluated the impact of altered predator diversity on the abundance and movement 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 four predator species, we found that on average a diverse group of predators reduced vector abundance but stimulated vector movement more so than single predator species. When we evaluated the indirect effect of predators on pathogen prevalence in wheat plants we found that predator impacts on vector populations did not cascade down to impact pathogen prevalence in a predictable manner; there was no difference in the proportion of plants infected with regard to predator diversity treatment.  This result could be due to the fact that while predators reduce vector abundance, they also stimulate vector movement, thereby increasing the frequency of contact and pathogen transmission between vectors and susceptible host plants. Therefore, we conclude that it will be the relative strength of predator effects on both vector abundance and movement that will ultimately determine how predators and predator diversity impact pathogen prevalence in a host plant community.