Do experimental drought stress and species' drought sensitivity influence herbivory in tropical tree seedlings?

Liza Comita and 4 other contributors

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    In tropical forests, drought and herbivory represent two potent stresses on seedlings. Climate change is expected to increase the frequency of severe droughts in many tropical forests, which may influence seedling vulnerability to herbivores if drought stress affects seedling palatability. Furthermore, contrasting selective pressures in wetter vs drier forests could mean that species well-adapted to herbivores are less drought resistant and vice versa. In this study, we measured seedling performance and herbivory in a common garden experiment where seedlings of 15 tree species were subjected to irrigation or rainfall exclusion treatments across two dry seasons in Panama. Water manipulation had no effects on foliar herbivory during the experiment for all species combined and for 14 of the 15 focal species when analyzed separately. There was large variation among species in herbivore damage, but no relationship between the sensitivity of species to drought and the amount of herbivory they experienced. Altogether, our findings suggest that increasing drought stress is unlikely to directly alter tropical tree seedling susceptibility to herbivore attack in this forest. Additional studies are needed to determine whether drought alters tropical plant-herbivore interactions via other mechanisms, such as through changes in herbivorous insect communities and/or increases in fitness costs of herbivory. Abstract in Spanish is available with online material.