Abstract
Changes in predator species richness can have important consequences for ecosystem functioning at multiple trophic levels, but these effects are variable and depend on the ecological context in addition to the properties of predators themselves. Here, we report an experimental study to test how species identity, community attributes, and community structure at the herbivore level moderate the effects of predator richness on ecosystem functioning. Using mesocosms containing predatory insects and aphid prey, we independently manipulated species richness at both predator and herbivore trophic levels. Community structure was also manipulated by changing the distribution of herbivore species across two plant species. Predator species richness and herbivore species richness were found to negatively interact to influence predator biomass accumulation, an effect which is hypothesised to be due to the breakdown of functional complementarity among predators in species-rich herbivore assemblages. The strength of predator suppression of herbivore biomass decreased as herbivore species richness and distribution across host plants increased, and positive predator richness effects on herbivore biomass suppression were only observed in herbivore assemblages of relatively low productivity. In summary, the study shows that the species richness, productivity and host plant distribution of prey communities can all moderate the general influence of predators and the emergence of predator species richness effects on ecosystem functioning.
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Acknowledgments
We thank Carys Hutton, Liz Wheeldon and Matt Naish for their considerable efforts in helping us run these experiments, and to two anonymous reviewers for their constructive criticism of the paper. This work was funded by the NERC project NE\G010226\1 awarded to A. Wilby and K. Orwin.
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Communicated by Jason Tylianakis.
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Wilby, A., Orwin, K.H. Herbivore species richness, composition and community structure mediate predator richness effects and top-down control of herbivore biomass. Oecologia 172, 1167–1177 (2013). https://doi.org/10.1007/s00442-012-2573-8
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DOI: https://doi.org/10.1007/s00442-012-2573-8