Herbivory from Individuals to Ecosystems

Herbivores not only consume resources, but they are resources for other consumers. Consequently, they have much potential to mediate effects that cascade up and down trophic chains in ecosystems. The way those effects are mediated depends on individual-scale properties of herbivores including constraints determining resource limitation, herbivore feeding mode, the adaptive trade-off to balance nutrient intake and predation risk avoidance, and the need to maintain homeostatic balance of elemental chemistry in the face of widely varying elemental composition of plant resources. These factors determine the rates of ecosystem functions such as production, decomposition and nutrient cycling. This review integrates those factors to build a conceptual framework for looking at herbivore-mediated effects in ecosystems. The framework systematically resolves how herbivores and carnivores directly and indirectly interact with plants to shape ecosystem functions. It can be used to motivate new field experimentation aimed at elucidating mechanisms of trophic control of ecosystem function.