Effects of Gypsy Moth Establishment and Dominance in Native Caterpillar Communities of Northern Oak Forests

Abstract Little research has addressed the impacts of invasive-species establishment on native forest insect communities. Such information is lacking even for gypsy moth, Lymantria dispar (L.) (Lepidoptera: Erebidae), the most thoroughly studied invasive forest insect. We investigated the ecological impacts of gypsy moth on native species at sites in north-central Ontario, Canada, with and without significant histories of gypsy moth defoliation over a 2-year period. Patterns in native forest caterpillar communities are described using measures of species diversity and multivariate analysis. We documented a transition from low-level to dominant gypsy moth populations. Sites with different gypsy moth outbreak histories exhibited differences in rank-abundance distributions and dominance structures in the first year of the study; by the second year, gypsy moth was dominant at sites of both types irrespective of their previous defoliation history. Contrary to our predictions, we found that gypsy moth outbreak history had no significant effects on native caterpillar community diversity or structure. However, sites with currently high gypsy moth abundance demonstrated significant shifts in late-season caterpillar community structure. Our results suggest that observed community differences were due to the presence of a highly abundant folivore, and not to permanent shifts in the native community because of the introduction of an invasive species.