Microhabitat requirements of the uncompahgre fritillary butterfly (Boloria improba acrocnema) and climate change implications

Abstract The Uncompahgre fritillary butterfly ( Boloria improba acrocnema Gall LF, Sperling FAH (1980) A new high altitude species of Boloria from southwestern Colorado (Nyphalidae), with a discussion of phenetics and hierarchical decisions. J Lepidopterists’ Soc 34:230–252 1980) was listed as federally endangered in 1991 and is considered a habitat indicator for alpine ecosystem health. They are found on patches of Salix nivalis in isolated habitats of the San Juan Mountains, Colorado, USA. Here, we estimated historical B. i. acrocnema abundance from annual distance sampling (2003–2020) at seven sub-colonies and sampled current (July 2021) measurements of herbaceous coverage, soil moisture content, and slope, aspect, and elevation at 700 sample sites. We used regression models to test the effects of these microhabitat characteristics on historical abundance. Our results show that increases in slope from 11° to 31°, individual coverage of five alpine plant species ( S. nivalis , Geum rossii , Phacelia sericea , Noccaea fendleri , and Lewisia pygmaea ), and soil moisture content between 0.09 m 3 /m 3 and 0.38 m 3 /m 3 positively influence butterfly abundance. However, increases in elevation, bare ground coverage, and presence of Salix planifolia , Aster alpinus , Antennaria media , and Androsace chamaejasme were correlated with lower abundance estimates. Implications for insect conservation Effects of climate change which decrease coverage of these alpine plant species, allow encroachment of lower elevation species, or reduce soil moisture will decrease B. i. acrocnema abundance. These results emphasize the extinction risk of B. i. acrocnema due to range limitations and prolonged drought conditions in the Western U.S. By defining additional resource requirements of B. i. acrocnema , we can model climate effects on survivorship and consider nearby microhabitats that may be habitable by this endangered species.