Effects of resource availability on tolerance of herbivory: a review and assessment of three opposing models.

Although it is widely acknowledged that a plant's tolerance of herbivore damage depends on resource availability in the plant's environment, there is no consensus on whether higher resource levels lead to greater or to lower tolerance. The prevailing model, the compensatory continuum hypothesis (CCH), predicts that tolerance of herbivory should be greater in high-resource or low-competition conditions. The main rival hypothesis, the growth rate model (GRM), makes the opposite prediction: tolerance of herbivory should be greater in more stressful conditions. The tolerance predictions of a recently introduced model, the limiting resource model (LRM), are more flexible and depend on the type of resource and herbivore under consideration. We reviewed 48 studies (from 40 published articles) of plant tolerance of leaf damage in conditions differing in levels of light, inorganic nutrients, water stress, or competition. The results of 31%, 48%, and 95% of the studies were consistent with the predictions of the CCH, GRM, and LRM, respectively. Thus, by considering which resource is primarily affected by herbivory and which resource is limiting a plant's fitness, the LRM offers a substantial advance in predicting how tolerance will be affected by environmental differences in resource availability.