ABSTRACT for Ecological Society of America/Society for Ecological Restoration joint meeting in Tucson, AZ, August 4-9, 2002.

Extending the trophic cascade hypothesis from elk and aspen to butterflies

KLEINTJES, P. K. and S. M. FETTIG, University of Wisconsin-Eau Claire, Eau Claire, WI 54702, Bandelier National Monument, Los Alamos, NM 87544

Herbivory by wild ungulates influences the structure and composition of plant communities, but less is known about how such changes affect insect herbivores. In the Jemez Mountains, New Mexico, we used randomized ungulate exclosures (60-m x 60-m) in aspen-mixed conifer forest(n=5) and ponderosa pine grassland (n=4), to measure the response of butterflies to herbivory by high numbers of elk (Cervus elaphus), 1999-2001. We measured butterfly abundance and species richness as well as environmental variables, e.g., vegetation cover, blooming nectar species abundance and richness, forb and grass biomass, percent canopy, aspen density, in each site. Habitat use by radio-collared elk was determined by aerial surveys. We observed a total of 1879 butterflies belonging to 44 species. Butterfly abundance and species richness significantly differed among dates, treatment and dates*treatment in forest sites and among dates in grassland sites in 2001. Both butterfly abundance and species richness were positively correlated with forb biomass and aspen stem densities (0.5-2.0 m heights) while the distribution of aspen stem densities significantly differed among height classes and treatments. Ordination analyses indicate that community composition of late-summer flying butterflies was best explained by greater forb biomass, blooming nectar species richness and abundance, and aspen regeneration as a result of exclusion of ungulates. Our results suggest that high numbers of elk may limit montane butterflies associated with successional aspen communities and that both the ungulate herbivory and trophic cascade hypotheses regarding elk suppression of aspen may extend to insect herbivores.