Paradoxes of Poweshiek Skipperling (Oarisma poweshiek) (Lepidoptera: Hesperiidae): Abundance Patterns and Management of a Highly Imperiled Prairie Species

Abstract

Although Oarisma poweshiek sometimes occurred in localized abundance, its known range is centered on the highly decimated northern tallgrass prairie of North America. To aid its conservation, we analyze surveys from 1988 to 1997 of populations no longer being found. While we recorded 2403 individuals at 20 sites, five sites had 87% of individuals, while 12 sites had only 2% of individuals. Most surveys during O. poweshiek flight had zero individuals recorded. In peak vegetative characteristics for O. poweshiek, fire management had the highest mean abundance but the lowest median abundance and lowest percent occurrence compared to idling and haying. Mean abundance was by far the lowest in the first year postfire compared to longer since fire. Median abundance and percent unit surveys where O. poweshiek was found indicated higher abundances the longer since fire. Although this skipper occasionally exhibited super-recoveries after fire, the median result in fire-managed occupied sites was zero. In a few years, abundance appeared synchronized across many sites, either low (1993, 1997) or high (1994-1995). It is only through a constant focus on avoiding the worst-case scenario that the rare best-case scenario of long-term population persistence appears possible for O. poweshiek.

Conservation genetics of an endangered grassland butterfly (Oarisma poweshiek) reveals historically high gene flow despite recent and rapid range loss

“…The Poweshiek skipperling [ Oarisma poweshiek (Parker, 1870) (Lepidoptera: Hesperiidae)] is a grass‐feeding skipper native to the Midwestern United States and southern Manitoba. As recently as the 1990s, it was widespread and the most frequently and reliably encountered of the obligate‐prairie skippers in Minnesota (Dana, ); it is now only found in two counties in the United States and in one preserve in Canada (Swengel et al ., ; Swengel & Swengel, , ; United States Fish & Wildlife Service, ). Oarisma poweshiek were previously very easy to find and many sites had hundreds of them flying at once (Dana, ).…”

Status and Trend of Regal Fritillary (Speyeria idalia) (Lepidoptera: Nymphalidae) in the 4th of July Butterfly Count Program in 1977–2014

“…In a transect survey dataset of prairie butterflies, patterns of presence-absence and abundance largely agreed but abundance was the more powerful statistical measure [ 37 ]. However, for a different prairie butterfly with a highly skewed distribution of population abundances, both types of measure were valuable and complementary in characterizing the species' status and trend [ 38 ]. In 4JCs, Regal Fritillary was similarly skewed in distribution of population abundances ( Table 4 ).…”

Grass-skipper (Hesperiinae) trends in midwestern USA grasslands during 1988–2013

“…Butterfly survey totals can lack a normal distribution, so that the mean may be skewed toward the high abundance of a few sites when most other sites had few or no individuals found (e.g., as in Swengel and Swengel 2014). By analyzing at the scale of the site, rather than the region, each site was represented equally in statistical tests.…”