Local- and Landscape-Level Variables Related to Poweshiek Skipperling Presence in Michigan Prairie Fens

The Poweshiek skipperling Oarisma poweshiek, Lepidoptera: Hesperiidae is a historically common prairie butterfly with a range extending throughout prairie systems of the upper midwestern United States and southern Manitoba, Canada. Rapid, range-wide declines have reduced the number of verified Poweshiek skipperling locations to one in Manitoba prairie, one in Wisconsin prairie, and four in prairie fens in Michigan. Our objective was to investigate parameter suites with the potential to be biologically relevant to Poweshiek skipperling occupancy with the goal of informing conservation efforts. At 18 prairie fens categorized as occupied (n = 9) or unoccupied (n = 9), we collected information on plant biodiversity, water chemistry, soil chemistry, site geometry, and surrounding current and historical land cover at three spatial scales. To address the complexity of these systems, we used multiresponse permutation procedures and nonmetric multidimensional scaling to explore associations between variable groups thought to be relevant to Poweshiek skipperling (conditions for suspected larval host plants, system integrity, and agricultural influence) and occupancy categories. We used indicator species analysis to understand the relationships between plant biodiversity and Poweshiek skipperling occupancy at whole- and intrafen scales. Multiresponse permutation procedures analysis suggested that conditions for suspected larval host plants differed between occupied and unoccupied prairie fens. At the whole-fen scale, we identified 14 plant species associated with Poweshiek-occupied sites, including two purported larval host plants, Muhlenbergia richardsonis and Schizachyrium scoparium. At the intrafen scale, we identified 52 species associated with unoccupied Poweshiek sites, including many weedy species and those tolerant of inundated conditions. Our results can inform the evaluation of potentially suitable habitat for introduction and reintroduction efforts.