Although many researchers propose that the balance between costs of plant defenses and the cost of herbivory have influenced both the types of defenses a plant employs and the distribution of those defenses among plant structure, no study to date has fully evaluated these costs in a quantitative fashion nor has anyone determined how these costs are affected by the plant's access to light and other resources. To address this question, the relationship between costs of extrafloral nectar production in two closely related Passiflora species that differ in the range of light conditions in which they grow will be studied. The proposed project provides several advantages over previous approaches to the study of costs and benefits of defense. Extrafloral nectar, unlike many toxic chemical defenses, has a simple chemical composition and can be measured in a non-destructive fashion. Further, protection associated with extrafloral nectar production can be evaluated by comparing untreated plants to plants from which ants have been excluded. Finally, by using population projection matrices to model plant growth, the costs of defense and herbivory can be expressed in terms of a fitness component. Thus, extrafloral nectar-based ant defense may represent an ideal system for the study of costs and benefits of leaf defense.
