The effect of community-wide phytochemical diversity on herbivory reverses from low to high elevation

1. Theory predicts that a large fraction of phytochemical diversity – the richness of individual chemical compounds produced by plants – governs the complexity of interactions between plants and their herbivores. While the effect of specific classes of chemical compounds on plant resistance against herbivores has been largely documented, the effect of community-level variation in phytochemical diversity on plant-herbivore interactions has so far received minimal consideration. 2. We hypothesized that plant communities bearing on average higher levels of phytochemical diversity should sustain lower herbivory rates, overall. Yet, the magnitude of this effect could vary across different environmental conditions, potentially because of climate- mediated effects on phytochemical production and changes in herbivore community richness and composition. 3. To address these hypotheses, we used previous knowledge of species-level phytochemical make-up for more than 400 plant species of the S...