Management regime and habitat response influence abundance of regal fritillary (Speyeria idalia) in tallgrass prairie

Abstract

The >2,570,000-ha Flint Hills ecoregion of Kansas, USA, harbors the largest remaining contiguous tract of tallgrass prairie in North America, a unique system, as the remainder of North America's tallgrass prairie has succumbed to development and conversion. Consequently, the loss and degradation of tallgrass prairie has reduced populations of many North American prairie-obligate species including the regal fritillary (Speyeria idalia) butterfly. Population abundance and occupied range of regal fritillary have declined >99%, restricting many populations to isolated, remnant patches of tallgrass prairie. Such extensive decline has resulted in consideration of the regal fritillary for protection under the Endangered Species Act. Although it is widely accepted that management practices such as fire, grazing, and haying are necessary to maintain prairie ecosystems, reported responses by regal fritillary to these management regimes have been ambiguous. We tested effects of prescribed fire across short, moderate, and long fire-return intervals as well as grazing and haying management treatments on regal fritillary density. We also tested the relative influence of habitat characteristics created by these management regimes by measuring density of an obligate host plant (Viola spp.) and canopy cover of woody vegetation, grasses, forbs/ferns, bare ground, and litter. We found density was at least 1.6 times greater in sites burned with a moderate fire-return interval vs. sites burned with short and long fire-return intervals. Overall management regardless of fire-return interval did not have an effect on density. Percent cover of grass had the strongest positive association, while percent cover of woody vegetation had the greatest negative effect on density. Our results indicate that patch-burning is a viable and perhaps even ideal management strategy for regal fritillary in tallgrass prairie landscapes. Additionally, these results elucidate the importance of fire, particularly when applied at moderate-return intervals to regal fritillary, and corroborate a growing suite of studies that suggest fire is perhaps not as detrimental to populations of regal fritillary as previously believed.

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

“…Generally speaking, our model findings are consistent with other studies investigating land cover as an indicator of butterfly habitat quality, and thus abundance (Early et al, 2008;Perovi c et al, 2015;Pogue et al, 2016;Post van der Burg et al, 2020;Slancarova et al, 2014). Specifically, the effects of both grassland and forest cover appear consistent with other studies of regal occurrence and indicate that regals prefer to use locations surrounded by grassland with little to no tree cover (Caven et al, 2017;McCullough et al, 2019;Powell et al, 2007;Ries & Debinski, 2001;Selby, 2007). However, this was not a consistent pattern in the sense that our maps of abundance follow the distribution of grasslands.…”

“…Around each grassland pixel, we computed the amount of grassland and forest found within 1 km. Others have pointed out that abundances of this species are likely higher in areas with larger expanses of intact grassland and lower amounts of forest cover (McCullough et al, 2019). We also computed the distance of each grassland pixel to the nearest human‐developed area, which served as an index of how easy a pixel was to access by surveyors.…”

“…One challenge arising when working with citizen science databases is that the data they contain are often reported at a spatial scale much different from the underlying process generating the observations. For instance, the environmental characteristics believed to govern whether a regal fritillary is likely to be present at a point on the landscape include the presence of certain plant species, the presence of grassland or forest cover, as well as weather conditions (Antonsen et al, 2021; Mason, 2001; McCullough et al, 2019). These environmental characteristics are likely to be localized and specific to a point in space (e.g., the location of a certain species of plant).…”

Fire regime shapes butterfly communities through changes in nectar resources in an Australian tropical savanna

“…Davis et al (2007) reported the majority of species they recorded in tallgrass prairie responded positively to litter. McCullough et al (2019) reported densities of the prairie specialist Speyeria idalia increased with litter cover. Callophrys irus , a rare fire‐dependent butterfly in the Eastern United States, pupates in litter above the soil 92% of the time (Selfridge et al, 2019).…”

Cattle grazing results in greater floral resources and pollinators than sheep grazing in low‐diversity grasslands

“…We burned three‐fourth of each pasture by the end of this study, but a full application of patch‐burn grazing would mean that each unit in the pastures have received fire at least once (Allred, Fuhlendorf, Engle, et al, 2011 ; Archibald et al, 2005 ; Fuhlendorf & Engle, 2004 ). More years of fire application would also result in greater sample size for each time since fire benchmark (recently burned, 1, 2, 3 years since fire) and more statistical power to determine how time since fire affects specific species and the pollinator community (McCullough et al, 2019 ; Moranz et al, 2012 , 2014 ; Potts et al, 2003 ). Overall butterfly abundance and richness were higher in cattle pastures, but our community analysis did not find a strong association between grazer treatment or site characteristics and patterns of variation in the butterfly community.…”