Introduction

Growth and reproduction add biomass to plant communities. Disturbances remove biomass. Thus the amount of vegetation in an area will be controlled by the balance between the former (primary production) and the latter. Disturbances can be either abiotic (fire, flooding, landslides) or biotic (herbivory, burrowing, trampling). Herbivory is of particular interest as a disturbance because it is biotic and often selective, and the relationships between plants and herbivores are continually evolving.

It is important that one be aware that the study of herbivory, or plant-herbivore interactions, is made difficult by the many possible ways, both direct and indirect, by which herbivores can influence plants. Further, the relationship is not merely one-way because plants simultaneously influence herbivores. The study of plant–herbivore interactions has led to topics as wide ranging as animal nutrition, the evolution of teeth and guts, kinds of plant defenses, the physiological responses of plants to losing leaves or seeds, and the impacts of herbivores upon soils. Figure 7.1 outlines some of the possible interactions between plants and herbivores.