Plant characteristics drive ontogenetic changes in herbivory damage in a temperate forest

Abstract

Abstract Understanding ontogenetic differences in plant defenses and herbivory damage is crucial for obtaining a better understanding of plant life‐history strategies, community assembly, and dynamics. Although many studies have compared plant defenses or herbivory damage between ontogenetic stages (e.g. sapling vs. adult), how the effects of plant characteristics on leaf herbivory damage change during plant ontogeny has rarely been examined across species or in a species‐rich natural community. To elucidate the effects of plant characteristics, we compared the relationships of leaf herbivory by insects with stem density, plant size, and leaf traits between saplings and adults for almost all co‐occurring woody species (56 species, ranging from rare to abundant) in a Japanese temperate forest. In most species, adults were larger, fewer in number, and had leaf traits that were potentially less favorable to herbivores (e.g. stronger, or with more phenolics). In contrast, we observed species‐specific directions of changes in herbivory damage between adults and saplings with plant phylogeny or density having no clear effect. The relationships between some plant traits and herbivory damage were ontogeny dependent, indicating a shift from chemical to physical defense as plants mature, although most of the species characteristics studied were highly correlated between stages. Such ontogeny‐dependent relationships between plant traits and herbivory damage could cause variation in the ontogenetic changes in herbivory damage among species depending on the value of plant traits. Moreover, the direction and magnitude of the effects of ontogenetic differences in species traits on the ontogenetic differences in herbivory damage varied depending on the traits. Together, these factors could have caused the observed ontogenetic changes in herbivory damage among species. Synthesis. Our study demonstrated how relationships between plant characteristics and herbivory damage can change ontogenetically across many coexisting woody species in a forest community, suggesting that plant traits may perform different functions related to herbivory at different ontogenetic stages. This has rarely been considered in previous dualistic comparisons of individual traits and herbivory damage between ontogenetic stages, and it is vital for understanding plant life‐history strategies across stages in relationships with herbivores in natural communities.