Defense and Dynamics in Plant-Herbivore Systems

Recent theory about interactions between plants and their herbivores focuses on properties of individual plants that affect their resistance to herbivores, and it extrapolates from these individual properties to those of whole communities. In this paper I question three major assumptions of this approach—costs of defenses, basic differences between classes of defenses, and step-wise coevolution—and recast the theory from a different community perspective. I propose that major differences in defenses between plants with very different life-history characteristics arise from differences in community structure, especially the numbers of herbivore species involved in the interactions. In particular, because of the diffuse pattern of herbivory on persistent plants, a new model of coevolution—diffuse coevolution—becomes appropriate when many species are involved. Complex interacting assemblages have special properties that cannot be derived just by summing up all of the simple interactions that occur.