Entomology

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Author: search.filters.author.Bracken, MatthewSubject: search.filters.subject.herbivory

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    Herbivore metabolism and stoichiometry each constrain herbivory at different organizational scales across ecosystems
    (Ecology Letters, 2009) Hillebrand, Helmut; Borer, Elizabeth; Bracken, Matthew; Cardinale, Brad; Cebrian, Just; Cleland, Elsa; Elser, James; Gruner, Daniel; Harpole, Stanley; Ngai, Jackie; Sandin, Stuart; Seabloom, Eric; Shurin, Jonathan; Smith, Jennifer; Smith, Melinda
    Plant-herbivore interactions mediate the trophic structure of ecosystems. We use a comprehensive data set extracted from the literature to test the relative explanatory power of two contrasting bodies of ecological theory, the metabolic theory of ecology (MTE) and ecological stoichiometry (ES), for per-capita and population-level rates of herbivory across ecosystems. We found that ambient temperature and herbivore body size (MTE) as well as stoichiometric mismatch (ES) both constrained herbivory, but at different scales of biological organization. Herbivore body size, which varied over 11 orders of magnitude, was the primary factor explaining variation in per-capita rates of herbivory. Stoichiometric mismatch explained more variation in population-level herbivory rates and also in per-capita rates when we examined data from within functionally similar trophic groups (e.g. zooplankton). Thus, predictions from metabolic and stoichiometric theories offer complementary explanations for patterns of herbivory that operate at different scales of biological organization.
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    Consumer versus resource control of producer diversity depends on ecosystem type and producer community structure
    (Proceedings of the National Academy of Sciences of the USA, 2007) Hillebrand, Helmut; Gruner, Daniel; Borer, Elizabeth; Bracken, Matthew; Cleland, Elsa; Harpole, Stanley; Ngai, Jacqueline; Seabloom, Eric; Shurin, Jonathan; Smith, Jennifer
    Consumer and resource control of diversity in plant communities have long been treated as alternative hypotheses. However, experimental and theoretical evidence suggests that herbivores and nutrient resources interactively regulate the number and relative abundance of coexisting plant species. Experiments have yielded divergent and often contradictory responses within and among ecosystems, and no effort has to date reconciled this empirical variation within a general framework. Using data from 274 experiments from marine, freshwater, and terrestrial ecosystems, we present a cross-system analysis of producer diversity responses to local manipulations of resource supply and/or herbivory. Effects of herbivory and fertilization on producer richness differed substantially between systems: (i) herbivores reduced species richness in freshwater but tended to increase richness in terrestrial systems; (ii) fertilization increased richness in freshwater systems but reduced richness on land. Fertilization consistently reduced evenness, whereas herbivores increased evenness only in marine and terrestrial ecosystems. Producer community evenness and ecosystem productivity mediated fertilization and herbivore effects on diversity across ecosystems. Herbivores increased producer richness in more productive habitats and in producer assemblages with low evenness. These same assemblages also showed the strongest reduction in richness with fertilization, whereas fertilization increased (and herbivory decreased) richness in producer assemblages with high evenness. Our study indicates that system productivity and producer evenness determine the direction and magnitude of top-down and bottom-up control of diversity and may reconcile divergent empirical results within and among ecosystems.