Evolutionary Trade-Offs in Plants Mediate the Strength of Trophic Cascades

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Science  26 Mar 2010:
Vol. 327, Issue 5973, pp. 1642-1644
DOI: 10.1126/science.1184814

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Trophic Trade-Offs

There have been many attempts to document and explain the effects of predators on plant biomass in so-called “trophic cascades.” Theory suggests that fast-growing plants are relatively undefended and suffer more from herbivory, which implies a functional trade-off between investment in traits relating to growth and defensive strategies. Mooney et al. (p. 1642; see the Perspective by Hambäck) compared responses to fertilization and aphid predators in 16 milkweed species. As predicted, interspecific variation in the strength of top-down control in terms of a tradeoff with growth was observed.


Predators determine herbivore and plant biomass via so-called trophic cascades, and the strength of such effects is influenced by ecosystem productivity. To determine whether evolutionary trade-offs among plant traits influence patterns of trophic control, we manipulated predators and soil fertility and measured impacts of a major herbivore (the aphid Aphis nerii) on 16 milkweed species (Asclepias spp.) in a phylogenetic field experiment. Herbivore density was determined by variation in predation and trade-offs between herbivore resistance and plant growth strategy. Neither herbivore density nor predator effects on herbivores predicted the cascading effects of predators on plant biomass. Instead, cascade strength was strongly and positively associated with milkweed response to soil fertility. Accordingly, contemporary patterns of trophic control are driven by evolutionary convergent trade-offs faced by plants.

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