Investigating population status, habitat, and ecological interactions for the Sand Mountain blue butterfly, one of North America's most geographically restricted butterflies
Euphilotes pallescens arenamontana, the Sand Mountain blue butterfly, is a subspecies of the pallid blue and is endemic to Sand Mountain, a dune system in central Nevada, USA. Eriogonum nummulare, Kearney's buckwheat, is the larval host plant and primary nectar resource and can be found bordering the western edge of the dune system as well as in isolated pockets on the eastern side of the dunes. The butterfly is of conservation concern due to its small geographic range (a single locality) and restricted habitat association as well as recreational activities at Sand Mountain. Motivated by the rarity of the butterfly and associated concerns, we ask the following questions: 1) is the E. p. arenamontana population stable across years? 2) are there habitat features that predict the presence and abundance of caterpillar and adult life stages? 3) to what extent has the vegetation composition changed over the years at Sand Mountain? and 4) which insects at Sand Mountain are using and potentially pollinating E. nummulare? To address the population question, adult butterfly counts were conducted in the years 2006, 2022, and 2023 with meandering surveys at 27 sites along a 3 mile transect from the northeast end to the southwest extent of the dune complex at Sand Mountain. Variables that include the cover of E. nummulare, disturbance, and ant presence were quantified at 67 plots and used to examine habitat association for caterpillars and adult butterflies. A slight decline is apparent in the weekly average of butterflies seen between 2006 and the more recent years of 2022 and 2023. The best predictors for caterpillar presence in a plot are inflorescences of Kearney's buckwheat, the abundance of ants, and the total numbers of adult butterflies, while precent cover of the focal plant in a plot is the best predictor of adult butterfly presence. Vegetation composition appears to have changed over the years, comparing 2006 and 2024, with fewer E. nummulare plants and the presence of new plants including nonnative and invasive Bromus tectorum. Insects in the order Hymenoptera were found to be carrying the most E. nummulare pollen, and within that order the family Crabronidae was associated with the highest densities of pollen. We use these results to assess the conservation status of E. p. arenamontana and to consider whether additional protections are needed for this rare butterfly, its host plant, and mutualist ant partners.
Buckwheat, Butterfly, Endemic, Sand Dune
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