Predator diversity impacts herbivore abundance and behavior with cascading effects on the prevalence of a vector-borne plant pathogen
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There is growing concern about the loss of biodiversity; particularly of organisms at higher trophic levels, such as predators, which face a disproportionately higher risk of extinction. As predator diversity declines there may be consequences for critical ecosystem processes such as disease dynamics, and/or valuable ecosystem services like natural pest suppression. In this study, I examine the impact of declining predator diversity on 1) the strength and spatial stability of suppression of a generalist sap-feeding insect, the bird cherry-oat aphid Rhopalosiphum padi, residing in wheat (Triticum aestivum) habitats, and 2) the mechanism contributing to any observed predator diversity effects on aphid suppression. Furthermore, I evaluate 3) any cascading impacts of predator diversity loss on the prevalence of a plant pathogen, cereal yellow dwarf virus, which is vectored from plant to plant exclusively by aphids. By manipulating predator species richness and identity in experimental mesocosms in the laboratory, greenhouse and field settings, I found that predator diversity enhanced both the overall strength and spatial stability of herbivore suppression across the habitat. The greater suppression of aphid populations by diverse predator communities was attributed, at least in part, to a species identity effect whereby more diverse predator assemblages were statistically more likely to contain the predator species exhibiting the highest rate of aphid consumption. Predator diversity did not alter the prevalence of the aphid-vectored plant pathogen; however, the presence of predators significantly reduced pathogen prevalence by stimulating the movement and altering the feeding behavior of pathogen vectors. These results suggest that conserving predator diversity in natural and managed ecosystems may enhance the magnitude and spatial consistency of herbivore suppression, and potentially diminish the prevalence of some vector-borne plant pathogens; however, the contributions of particular predator species may be greate
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