Post-fire associations of butterfly behavior, occupancy, and abundance with environmental variables and nectar sources in the Sierra Nevada, California

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Fire can change the quality of habitat for many taxonomic groups, including butterflies. The abundance of nectar-producing plants, and the volume and concentration of the nectar in those plants, peaks in the initial years following a fire. Laboratory and controlled experiments have demonstrated that butterflies may have preferences for different sugars in those nectar sources, especially sucrose. However, sugar preferences have not been quantified for an assemblage of butterflies in a field setting. In 2014 and 2015, we conducted butterfly and vegetation surveys within the Rim Fire boundary on the Stanislaus National Forest (Tuolumne County, California). We surveyed eight sites throughout the butterfly flight season in both years and four additional sites in 2015. We analyzed the sugar and sucrose masses, and relative proportion of sucrose, in 20 known nectar sources. We found no evidence that intensity of butterfly use was associated with sugar mass or concentration, mass of sucrose, or the relative proportion of sucrose. Instead, butterflies appeared to use any sources that were available to them indiscriminately.

  Fire also affects environmental attributes associated with the distribution, abundance, and reproduction of butterflies. Studies have demonstrated that species richness and abundance of butterflies respond to fire. However, the effects of fire on butterfly occupancy, and on environmental attributes that are associated with butterfly occupancy, are largely unknown. Abundance estimates are generally more-informative measures of population status than occupancy, but collecting data for abundance estimates is more time consuming than for estimating occupancy. We examined the extent to which butterfly occupancy and abundance in the first two years following the Rim Fire were associated with environmental attributes that were affected by fire. We also tested whether fire severity explained variation in the environmental attributes that we included in models of butterfly occupancy and abundance. We found that environmental attributes associated with occupancy of some species were also associated with the abundances of those species, although the consistency of associations varied. Burn severity affected environmental attributes that were associated with butterfly occupancy and abundance. Understanding how fire affects environmental attributes that are associated with occupancy and abundance can inform use of prescribed fire or management following wildfire. 

 

About the presenter:

 David Pavlik graduated from Northern Michigan University with a degree in zoology, and from the University of Minnesota with a master’s degree in conservation biology. He has worked for various research organization across the United States including the United States Fish and Wildlife Service, the United States Geological Survey, University of California- Davis, Tall Timbers Research Station, and Rocky Mountain Bird Observatory, among others. He has studied birds, butterflies and other invertebrates, and marine mammals. He serves as a member of the Michigan Bird Records committee and enjoys birding, hiking, fishing, and photography.