Abstract:
Being the most important herbivores in the tropics, insects play a key role in the trophic cascades and nutrient cycles of rainforest ecosystems. It is not fully understood, however, which drivers influence the biomass, abundance, individual size and functional community structure of these secondary consumers. In this study, we investigate the effects of morphological leaf traits such as leaf thickness, water content, physical resistance and specific leaf area on folivorous insect communities in the canopy of a primary tropical montane rainforest in South Ecuador. Via canopy fogging, we collected 52 community samples. Insects were assigned to five feeding guilds and their total and relative biomass, abundance and individual weights were modelled using leaf traits of the respective trees. We found that tree species identity was the main predictor of community structure. Leaf thickness and water content also played a significant role, the latter especially reducing the share of caterpillars within the community. Feeding guilds were differently affected by leaf characteristics: e.g. coleoptera and orthoptera showed no significant reaction to food quality parameters. Caterpillars again were the only group in which individual sizes were affected by leaf parameters. We assume that they respond more directly because of their need for efficient energy extraction and fast biomass accumulation rates. As water content was a main predictor in many of our models, we suggest that it be used as a measure of food quality in future research rather than N levels per dry mass because it better predicts nutrient levels in the fresh weight of leaves and it is fresh leaves that canopy-inhabiting folivorous insects consume.
