The Impact of Herbivory on Plants in Different Resource Conditions: A Meta-Analysis

Understanding how plant recovery from herbivory interacts with the resource environment is necessary to predict under what resource conditions plants are most affected by herbivory, and ultimately how herbivory impacts plant population dynamics. It has been commonly assumed that plants are generally best able to recover from herbivory when growing in high resource conditions, an assumption which is supported by some models (e.g., the continuum of responses model) but opposed by others (e.g., the growth rate model). The validity and generality of any effects of resources (light, nutrients, and water) on plant recovery from herbivory were tested with mixed-model, factorial meta-analyses using a log response ratio metric applied to plant growth and reproduction data from the ecological literature. In total, 81 records from 45 studies were included in the growth meta-analysis, and 24 records from 14 studies in the reproduction meta-analysis. High resource levels and the absence of herbivory both strongly increased plant growth and reproduction. There was no significant overall interaction between growth or reproduction after herbivory and resource conditions, but the interaction terms were significant for each plant functional group in the growth meta-analysis. Basal meristem monocots grew significantly more after herbivory in high resources, while both dicot herbs and woody plants grew significantly more after herbivory in low resources. A similar result was found in the 34.6% of growth records where exact- or overcompensation occurred. Overcompensation was more likely in high resources for monocots and in low resources for dicot herbs. The reproduction data set was too small to subdivide. These qualitative differences between monocot and dicot herbs and woody plants explain many of the contradictory results in the literature and show that no single current model can account for the responses of all plants to herbivory.