Oak species that have been planted outside of their range vary widely in the amount of herbivory they accumulate by native herbivores. This study assesses both evolutionary predictors (relationship to native oak) and trait-based predictors of herbivory on non-native oaks. We created an AFLP phylogeny of 57 oak (Quercus) taxa, which were grown outside of their ranges in a common garden at UC Davis Shields Oaks Grove that contained one abundant native oak (Q. lobata). We used this phylogeny to ask whether oaks that are more closely related to a local native receive more damage from two types of herbivores (chewers and miners) than distantly related oaks. We also assessed 11 leaf traits, which likely have a bearing on herbivore performance in order to determine which if any of these traits affect herbivory rates on non-native oaks.
We found that phylogenetic relatedness to a local native oak predicted both chewing and mining damage. Suites of plant traits were predictive of chewing damage but not mining damage, and these traits did not account for the phylogenetic trend in herbivory rates. This study suggests that ecological interactions between native species and introduced species are stronger when the introduced species is a close relative to a local native. This observation has broad implications for invasion biology and this trend may play a role in which species within a taxonomic group such as oaks can coexist in a community.