▪ Abstract  Recent theoretical studies suggest that the ability to tolerate consumer damage can be an important adaptive response by plants to selection imposed by consumers. Empirical studies have also found that tolerance is a common response to consumers among plants. Currently recognized mechanisms underlying tolerance include several general sets of traits: allocation patterns; plant architecture; and various other traits that may respond to consumer damage, e.g., photosynthetic rate. Theoretical studies suggest that tolerance to consumer damage may be favored under a range of conditions, even when the risk and intensity of damage varies. However, most of these models assume that the evolution of tolerance is constrained by internal resource allocation trade-offs. While there is some empirical evidence for such trade-offs, it is also clear that external constraints such as pollinator abundance or nutrient availability may also limit the evolution of tolerance. Current research also suggests that a full understanding of plant adaptation to consumers can only be achieved by investigating the joint evolution of tolerance and resistance. While tolerance to consumer damage has just recently received significant attention in the ecological literature, our understanding of it is rapidly increasing as its profound ecological and evolutionary implications become better appreciated.

Many studies of herbaceous plant populations have illustrated the potential of adjacent subpopulations to adapt to local ecological conditions. However, the extent to which local adaptation on a small geographical scale can occur in outcrossing tree populations is not well understood. In this study, we reciprocally transplanted acorns from adjacent subpopulations of northern red oak (Quercus rubra L.) occupying north-, southwest-, and west-facing slopes within a 4-ha plot in a Missouri oak-hickory forest. The quantitative character we measured was leaf damage by herbivores on first-year seedlings, because it reflects resistance to insect herbivores-a quantitative trait that could be under different selective pressures in dissimilar microhabitats. We found that seedlings showed the least damage when planted at the site of the maternal plant. This finding provides initial but strong evidence of local adaptation and illustrates that selection associated with leaf harbivory may have a strong impact on the genetic structure of local tree populations. Such a result is unexpected for a widely outcrossing species on such a small geographical scale but indicates that genetic structuring is possible within other plant populations occupying heterogeneous environments.