TRADE-OFFS AND CONSTRAINTS IN PLANT-HERBIVORE DEFENSE THEORY - A LIFE-HISTORY PERSPECTIVE

Trade-offs and constraints are key ideas in plant defense theory. Here I argue that trade-offs, such as those between defense and growth, ma y be better understood by incorporating insights from life-history stu dies. Specifically, I set out criteria for characterizing resource bas ed trade-offs, because these lie at the heart of current defense theor y. I show that defense theory is often supported by inappropriate evid ence from negative trait associations seen in the field, or from genet ic studies. Such evidence is inappropriate because trade-offs grounded in genetic constraints can differ fundamentally from those conceived in terms of limiting resources. In work on resource based trade-offs t here is often a failure to consider the critical issues of whether the resources involved are limiting, and whether this limitation is impos ed by the assimilatory capacity of the organism or by a shortage in it s environment. Another important consideration is whether a trade-off is between two traits that jointly consume all resources. Where this i s not the case, unforeseen trade-offs with ''third party traits'' may confound analyses. I discuss the practical issues of resolving these p roblems with plants, and present a program for future research on reso urce based trade-offs involving plant defense.