PS 13-115 - Butterfly abundance declines over 20 years of systematic monitoring in Ohio, USA

Monday, August 12, 2019
Exhibit Hall, Kentucky International Convention Center
Tyson M. Wepprich, Botany and Plant Pathology, Oregon State University, Corvallis, OR, Nick Haddad, Department of Integrative Biology, Michigan State University, Leslie Ries, Biology, Georgetown University, Washington, DC, Jeffrey R. Adrion, University of Oregon and Jerome Wiedmann, Ohio Lepidopterists
Background/Question/Methods

Ongoing defaunation, or the drastic loss of animal species and declines in abundances, threatens to destabilize ecosystem functioning globally. As resurveys over decades show extreme declines in insect biomass, we argue that the best source of data to assess insect defaunation comes from large-scale, systematic monitoring programs. Insect declines documented by systematic monitoring are heavily skewed towards European programs, with little known about insect abundance elsewhere. The focus of our study is evidence for long-term, region-wide declines in abundance across a diversity of species of an entire insect group in North America. We estimate the rate of change in total butterfly abundance and trends for 87 species using long-term, systematic monitoring counts by volunteers over 20 years at 104 sites in the Midwestern United States. We review findings from systematic monitoring of European butterflies for comparison. We test for the association of life-history traits and phylogenetic relatedness with species’ abundance trends.

Results/Conclusions

We show that the rate and breadth across species of butterfly declines in Ohio mirror those documented in long-term European monitoring. Total abundance is declining at 2% per year, with 33% fewer butterflies now as compared to 20 years ago. More than 2.5 times as many species have significant negative abundance trends compared to significant positive trends. Life-history traits associated with abundance trends suggest that species pre-adapted to warmer climates, with southern distributions and a greater number of annual generations, have more positive trends in abundance. Common species thought to exploit human-dominated landscapes are in decline, suggesting widespread environmental causes for butterfly trends. Multiple environmental changes such as habitat degradation, climate change, and agricultural practices may contribute to these declines in Ohio. Environmental changes will select winners and losers among species with different life-history traits, but our study demonstrates an ongoing defaunation in the butterflies across the phylogenetic tree with multiple potential causes.