Surrogate species are often used in endangered species research when the focal species is too rare to manipulate or too rare to be reliably encountered on the landscape. This strategy has often been critiqued because of natural history differences across individual species. We examined the differential responses of an endangered-surrogate butterfly pair to habitat restoration actions. St. Francis’ satyr (Neonympha mitchellii francisci) is an endangered butterfly found only at Ft. Bragg, NC where it occupies open, sedge-dominated wetlands. Historically, these wetlands were maintained by beavers and/or fires, disturbances which have declined dramatically in the southeastern US in the last century. To restore St. Francis’ satyr habitat, we implemented a “being beavers” experiment in which we cut trees and dammed creeks in factorial treatments. Initially, St. Francis’ satyrs were rare in our experimental sites so we measured behavioral and demographic responses of a surrogate species, Appalachian brown (Satyrodes appalachia). As St. Francis’ satyr populations grew following restoration, we were able to collect similar data on the endangered species as well. For both species, we conducted adult surveys and measured caterpillar survival to adult across treatments, characterized vegetation at adult locations, and recorded caterpillar behavior in the greenhouse.
Results/Conclusions
St. Francis’ satyr and Appalachian brown adults occupy different restoration treatments. Appalachian brown butterflies are most abundant in un-cut plots while St. Francis’ satyrs are most abundant in cut plots. Appalachian brown butterflies found in cut plots occupy microsites with significantly more canopy cover that St. Francis’ satyrs. Survival of Appalachian brown immature stages is lower in cut plots as opposed to St. Francis’ satyrs. This is likely driven by differences in caterpillar behavior. Early instar St. Francis’ satyrs feed closer to the ground and under more cover than do Appalachian brown caterpillars. Because cut plots are 3-5 degrees C warmer than un-cut plots, Appalachian browns are more likely to desiccate on the tips of sedge blades where they are exposed to direct sunlight. The different results of these two species highlight the importance of understanding the natural history of target organisms and their surrogate species when asking fine scale questions such as how targeted restoration actions affect demography. We argue that if these data are necessary to successfully manage endangered species habitat, it is likely necessary to conduct at least minimal experiments with the target endangered species.