Assessing abundance patterns of specialized bog butterflies over 12 years in northern Wisconsin USA

Abstract

During 2002-2013, we surveyed butterflies in three types of bogs (pristine but naturally fragmented). Of the 75 bogs surveyed, we established 29 bogs and 5 bog roadsides as long-term sites visited annually for 9-15 years. We studied patterns of ten butterfly species' flight periods, annual variation, trend in abundance over time, and abundance with respect to climatic variables. First observed date per year varied more for spring than summer species. Jutta arctic Oeneis jutta varied between dramatically high numbers in odd years and low numbers in even years in northeast Wisconsin. Elsewhere, Jutta arctic varied less between odd and even years, but muskegs had higher numbers in even than odd years, significantly so in north central Wisconsin. The most abundant bog affiliate (tyrphophile), brown elfin Callophrys augustinus, exhibited cyclic abundance over a 4-5 year period. The other species varied greatly in abundance among years but not in as distinctive annual patterns. The most northern specialist (tyrphobiont), purplish fritillary Boloria montinus, declined strongly. Its abundance significantly related to higher precipitation but not to temperature. Population trends for the seven other tyrphobionts did not relate to how southerly their ranges are. Trends in roadsides were less favorable than in bogs. Butterfly abundance had more significant correlations to climate variables related to moisture than to temperature. Based on abundance relationships to climate, a majority of the study species allied as dry steppe species (increasing in warmer, drier periods) and a minority as wetland species (increasing in cooler, wetter periods). The overriding factors determining the future of this butterfly fauna appear to be habitat degradation and potential climate change beyond the range of variation typically experienced in this region between glaciations.

Further evidence for a global decline of the entomofauna

“…Population changes are related to ecological traits of many insect species, including butterflies (Swengel and Swengel 2015; Wenzel 2016), planthoppers and Orthopterans (Schuch et al . 2012a).…”

“…2009). Transect surveys for 10 butterfly species living in undisturbed bogs in Wisconsin between 2002 and 2013 showed that three of the steppe species exhibited positive population trends, while three wetland species declined (Swengel and Swengel 2015). Over 35 years, richness of 159 butterflies declined at half of the 10 monitoring sites within the Sierra Nevada (California), with the greatest decline among ruderal species at lower altitudes; some ruderal species of higher altitudes also declined (Forister et al .…”

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

“…We also added one site complex in central Wisconsin (Buena Vista Grassland, Portage County) in 1997 specifically to search for regal fritillaries, as well as study other grassland butterflies and birds. At many other survey sites in Central and Northern Wisconsin, we had other primary survey goals but our visits there during summer also afforded valid assays for the regal fritillary: (1) six state-owned wildlife areas containing complexes of old fields (degraded grasslands) to study grassland species, especially birds; most were in counties within the regal’s historic range [42,43,44]; (2) >125 pine-oak barrens (prairie-like herbaceous flora with trees and shrubs intermixed) in Central and Northwestern Wisconsin to study the Karner blue ( Lycaeides melissa samuelis ), federally listed as endangered [45], and other barrens butterflies [40,46,47]; and (3) >10 barrens and heaths across Northern Wisconsin (north of Karner blue range); and (4) 75 bogs and 20 bog roadsides in Northern Wisconsin to study their butterfly community, which includes other butterfly species that feed on violets as larvae [48,49,50]. Most sites were conserved lands in private or government ownership (e.g., preserves, federal refuges, state parks, state wildlife areas, state, and county forest) or public rights-of-way.…”