Anti-herbivory chemical defense in plants: a note on the concept of cost

Most current work on anti-herbivory defense systems in plants assumes a cost associated with the production and maintenance of a given defense level. This hypothesis has been formalized in some theoretical studies, and it has been corroborated in some experimental ones. However, we still lack a precise and general definition of the cost concept that has ecological as well as evolutionary meaning while retaining its physiological relevance. Therefore, I propose such a definition and demonstrate how it can be applied to various questions. My proposition is along the same line as the important work by Gulmon and Mooney, namely, that the cost should be expressed as a loss in relative growth rate of somatic tissue, but I generalize their formalism an dextend it to include turnover and recirculation of defensive substances.