Complex Messages in Long-Term Monitoring of Regal Fritillary (Speyeria idalia) (Lepidoptera: Nymphalidae) in the State of Wisconsin, USA, 1988–2015

Abstract

The regal fritillary (“regal”) (Speyeria idalia) is endangered in Wisconsin, USA, and declining and at risk range-wide. During 1988–2015, we surveyed 24 known regal sites and >100 areas of potential habitat in Wisconsin. We recorded 9037 individuals in 742.7 km on the peak survey per year at occupied sites. At six sites surveyed over 5–25 years, we found regal fritillaries in only one year, mostly in the latter half of the study. The three populations in the state with more favorable trends than the median had a never-burned refugium and/or infrequent fire management. They also all had substantial amounts of grazing, haying, and/or mowing managements. Sites with trends below the regional median trend had frequent or moderate fire management, and either a diminishing never-burned refugium or none at all. Regal populations at sites with ≤15 ha of grassland have become undetectable. Nonetheless, Hogback, a slightly larger than 15 ha site, had the most favorable trend, a significant increase. Nearly all Wisconsin Regal populations known before 1990 declined to consistent non-findability, even though these were conserved sites. More favorable trends at more recently discovered populations may be attributable to species-specific habitat management protocols implemented in the 1990s. Two sites with better than median long-term trends represent the longest consistent land ownership of known Regal populations in the state. This wide range of population outcomes illustrates both the need for long-term monitoring and the challenges of explaining the outcomes. Despite evidence of increasing Regal dispersal, this species remains very localized, indicating the unsuitability of the wider landscape as regal habitat. The number of significantly declining or no longer detectable populations in Wisconsin indicates an ever more adverse landscape for this species. Sites will need to have habitat characteristics that are ever more optimal in a wide range of climatic conditions for Regal populations to persist.

Perishing rich, expanding poor: Demography and population genetic patterns in two congeneric butterflies

“…Using transect counts, Swengel (1997) estimated adult densities of 2130, 800 and 290 individuals km −2 for the sympatric S. cybele (Fabricius, 1775), S. aphrodite (Fabricius, 1787) and S. idalia , respectively, at American Midwest prairie remnants, with the most threatened species being locally least abundant. Swengel and Swengel (2001) obtained consistently higher (≈3–6 times) transect counts for the less threatened S. aphrodite than for the declining S. idalia in a 10‐year study in Wisconsin. Low transect counts were also reported for the rapidly declining A. adippe in Britain (Ellis et al, 2011).…”

Point‐scale habitat and weather patterns influence the distribution of regal fritillaries in the central United States

“…This could have implications for the future persistence of this species if patterns of precipitation and temperature change in the future. Swengel and Swengel (2017) indicated that regal distributions have been gradually shifting northward and that this trend would likely continue as average temperatures increase in the Great Plains and Midwest. Our model allowed us to examine a simple scenario in which we simulated a systematic 2°C increase across the region.…”

Speyeria (Lepidoptera: Nymphalidae) Conservation

“…It is restricted to xeric tallgrass prairie remnants and it is rare or absent from former range east of the Appalachians. There are many extant populations, but the species has suffered severe population declines and its range continues to contract [ 20 ] S. idalia is almost gone from areas east of the Mississippi River, and it is imperiled in Illinois, Indiana, Pennsylvania, Virginia, and Wisconsin [ 20 , 21 ]. The biggest obvious threat to S. idalia is loss of its prairie habitat to development and agriculture, and the principal conservation need is to protect and manage its remaining prairie habitat [ 22 ].…”

“…The majority of habitat losses have resulted from human activities, including land development for agriculture, commercial, and residential uses, but climate change now represents an additional risk factor. In some cases, Speyeria habitat has been reduced in a mosaic pattern, leaving relatively small islands of suitable habitat that may be inadequate for long-term population survival [ 21 , 26 ]. In addition to the inbreeding and reduced gene flow problems mentioned previously, small populations also face an increased risk of extinction from stochastic events such as severe weather or fires [ 79 ].…”