Within-crown variability in herbivore performance and leaf traits

Functional trait variation within individual plants is predicted to have important ecological consequences. However, our understanding of the sources contributing to subindividual trait heterogeneity, and the ramifications thereof, is poor.
In a common garden, we sampled multiple genotypes of mature trembling aspen (Populus tremuloides) at different vertical crown levels and quantified the contributions of genetic, spatial and biotic (herbivory) factors to subindividual morphological and chemical leaf trait variance. Bioassays using gypsy moth (Lymantria dispar L.) caterpillars were conducted to study impacts of spatial and genotypic factors on insect performance.
Crown position was the primary source of subindividual variation in leaf morphology and explained more of the variance in morphological traits than tree genotype. Effects of spatial, genetic and biotic factors on within-crown chemistry were highly compound-specific. For many compounds, changes in within-crown concentrat...