The Effect of Resource Stress on Goldenrod's Tolerance of Folivory Depends More on the Identity of the Stress than on the Severity of the Stress

It is widely accepted that the levels of resources in a plant’s environment can influence the plant’s ability to compensate for (i.e., tolerate) damage by herbivores. However, predicting the direction of the influence has proven difficult. Here, we report on a greenhouse study in which individuals of Solidago altissima were exposed to factorial combinations of light and fertilization levels to investigate how different types of stresses affect plants’ ability to tolerate leaf damage by larvae of the beetle Trirhabda virgata. Shade stress reduced the plants’ tolerance of herbivory, while nutrient stress had no effect on tolerance. These results did not completely fit the predictions of any of the three predominant models for the effects of resource levels on herbivory tolerance, but they were best explained by the Limiting Resource Model (LRM). We discuss why the results of this study, as well as some other recent studies, may not exactly fit the predictions of the LRM. We highlight examples in which anomalous results have led to novel insights into factors that affect plants’ ability to compensate for herbivore damage.