Presence of substitute diets alters plant resistance to specialist and generalist herbivores: a meta-analysis

Abstract

How herbivores respond to resource heterogeneity is important for predicting plant resistance to herbivores. Experimental studies thus far have revealed that herbivore responses differ depending on whether herbivores are offered single or multiple plant types, but the reports have rarely been combined. Here, we conducted a meta-analysis of 47 publications on choice and no-choice experiments to reveal how the presence/absence of multiple plants (i.e., choice/no-choice conditions) alters the extent of behavioral avoidance by herbivores. The herbivore diet breadth and response traits (feeding, growth, or oviposition) explained a significantly large amount of heterogeneity in the herbivore response under choice and no-choice conditions. In contrast, a small amount of heterogeneity was explained by the herbivore types (vertebrates, exophagous, or endophagous invertebrates), plant resistance traits (chemical or nonchemical), plant life form, and relatedness of plant pairs (intraspecific or interspecific) as well as interactions between the herbivore and plant characteristics. Compared with the no-choice conditions, specialist herbivores further avoided suboptimal plants under choice conditions. Generalist herbivores more evenly utilized optimal and suboptimal plants under choice conditions. The avoidance of suboptimal plants under choice conditions was the most prominent in oviposition response. Thus, our meta-analysis found that herbivore characteristics rather than plant traits were more responsible for driving behavioral avoidance by herbivores to a particular plant. The contrasting response between specialist and generalist herbivores to plant heterogeneity may be more ubiquitous than previously thought.