From the: Proceedings of the 6^th Symposium of Biological Research in the Jemez Mountains, New Mexico, January 24^th, 2002.

Butterflies, elk and aspen: what’s the connection?

P. K. Kleintjes¹ and S. A. Fettig²

Herbivory by wild ungulates influences the structure and composition of plant communities, however less is known about how such changes affect the species richness and abundance of insect herbivores that utilize the same plant resources. Browsing and grazing by domestic ungulates is known to have both negative and positive effects upon butterflies, but what about wild ungulates? In the Jemez Mountains of New Mexico, numbers of elk have exponentially risen over the past 40 years causing observable changes in plant community structure. It was our objective to measure the response of butterflies to these potential changes in plant community structure and resource availability. During the summers of 1999-2001, we utilized 9 randomized and replicated elk exclosure and reference areas (5 mixed conifer (MC) and 4 ponderosa grassland (PG)) in Bandelier National Monument. In each site we measured butterfly abundance and species richness as well as various environmental variables, e.g., vegetation cover, blooming nectar plant abundance and species richness, forb and grass biomass, aspen density etc. Numbers of radio-collared elk were also monitored and mapped via aerial surveys. We observed a total of 1879 butterflies belonging to 44 species represented by six families. In PG sites, butterfly abundance and species richness significantly differed among sampling periods but not by treatments. In MC sites, species richness and abundance significantly differed for date and treatment in 2001 and abundance also differed for date* treatment. (2way repeated measures ANOVA’s). Both butterfly abundance and butterfly abundance (r²=0.72, p<0.05) and species richness (r²=0.66, p<0.05) were positively correlated with non-woody forb biomass and (0.5-2.0m ht) aspen stem densities (all r²’s >0.48, p<0.05). In the PG and MC sites, no significant relationships resulted from comparisons between the frequency of all blooming forbs, blooming forb richness or the frequency of the most abundant blooming forbs and butterfly abundance or species richness for the summer. However, in mid-late summer 2001, at the time more elk are in found in MC habitat, we found a strong correlation between the frequency of Potentilla spp in bloom and a select group of butterfly species (Speyeria cybele, S. hesperis, S. mormonia, Cercyonis oetus and Plebeius icarioides). We also found a strong relationship between the abundance of these five butterfly species and forb species richness (r²=0.65, F=17.79, p<0.05) as well as overall butterfly species richness and forb species richness (r²=0.61, F=15.2, p<0.05). Results of ordination analyses indicate that the mid-late summer butterfly communities, are responding to the presence of high numbers of elk in mixed conifer habitats and differences in the butterfly communities/site are best explained by greater forb biomass, blooming nectar species richness and abundance (esp. Potentilla spp) and aspen regeneration as a result of the exclusion of ungulate browsing and trampling.

¹Department of Biology, University of Wisconsin, Eau Claire, WI 45729; ph: 715-836-4166, FAX 715-836-5089, email:kleintpk@uwec.edu.

²Bandelier National Monument, HCR1, Box 1 Suite 15, Los Alamos, NM 87544; ph: 505-672-3861, ext.546, FAX:505-672-9607; email: stephen_fettig@nps.gov.