Résumé
1. A key issue in plant/herbivore interaction research is to understand which plant traits drive differences in herbivore damage. Variation in chemical, physical or phenological traits of plants may all modulate the degree of herbivore damage among species and individuals, yet the relative importance of these factors is still subject to debate, particularly in species-rich systems such as tropical rain forests.
2. To address this issue, we quantified leaf herbivore damage in 28 common tree species of the Yasuni forest dynamic plot (YFDP) in the Ecuadorian Amazon over 11 months. Census data from the YFDP allowed us to quantify several aspects of tree ecology potentially affecting herbivory including leaf turnover and spatial distribution patterns. We measured six chemical, eight physical and four ecological traits of the focal species. Using a combination of multivariate analyses and phylogenetic generalized linear regression model (PGLS), we assessed trade-offs between physical and chemical traits and the relative effect of all these traits on leaf herbivore damage.
3. Herbivore damage was highly variable among species and individuals, with leaves on average displaying damage over 13.4% (2.5-29.5%) of their area. We found no significant trade-off between physical and chemical defences for the 28 studied tree species. Overall, leaf size, shearing resistance, cellulose, ash content and leaf size x ash were the best predictors of herbivore damage. Surprisingly, condensed tannins and latex did not significantly correlate with herbivore damage. In addition, we found no relationships between herbivory and local tree density. However, we did find a weak effect of tree clustering and strong effect of tree leaf turnover rates on herbivore damage.
4. Synthesis. In the western Amazon, leaves are defended against herbivores through a combination of physical (toughness), chemical (toughness-related elements), and phenological (rapid leaf replacement) characteristics that do not appear to be subject to obvious trade-offs. Conventional strategies, such as condensed tannins or latex, do not seem to be strongly involved as a defence against herbivores in this community.