META-ANALYSIS OF SOURCES OF VARIATION IN FITNESS COSTS OF PLANT ANTIHERBIVORE DEFENSES

Abstract

Plant defense theories predict that allocation to antiherbivore defenses should impose a cost on plants, manifested as a reduction in growth and reproduction. However, the empirical evidence for the existence of such trade-offs is conflicting, suggesting that significant fitness costs of defense arise in some circumstances but not in others. A meta-analysis of 70 studies assessing the relationship between measures of plant defense and growth or reproduction has been conducted to examine the relative importance of several potential sources of variation in the fitness costs of defense. The magnitude of fitness costs varied depending on whether they were measured at the level of phenotype or genotype. The mean magnitude of among-genotype correlations (AGCs) between defense and fitness measures (r = −0.30) was higher than that of among-phenotype correlations (APCs; r = −0.15). Moreover, AGCs tended to be more negative when defense was assessed as the inverse of herbivore densities or damage rather than in ter...