Influence of climate variables and landscape changes on butterfly population declines at protected areas in Illinois, USA

Nicole B. Kucherov and Kevin Matteson, Biology, Miami University, Oxford, OH, Emily Minor, Institute for Environmental Science and Policy, University of Illinois, Chicago, IL, Philip P. Johnson, Department of Biological Sciences, University of Illlinois at Chicago, Chicago, IL, Doug Taron, Chicago Academy of Sciences, Chicago, IL

Background/Question/Methods
Despite increasing concern regarding broad-scale declines in insects, there are few published long-term, systematic butterfly surveys in North America, and fewer still that have incorporated the influence of changing climate and landscape variables. In this study, we analyzed 20 years of citizen science data at seven consistently-monitored protected areas in Illinois, U.S.A. We examined potential drivers of community change, including precipitation, temperature, and land cover change. We also investigated shifts in overall butterfly community composition, the degree of biotic homogenization through time, and changes in butterfly functional group abundance and richness. We used a model selection approach, with generalized linear mixed effects models (GLMM), to examine the effect of time, climate, and land cover on total butterfly richness, abundance, and functional groups. To test for biotic homogenization of butterfly communities from 1999 to 2018, we evaluated beta diversity between communities for each 5-year period.
Results/Conclusions
We found that butterfly abundance and richness increased in warmer years. Surprisingly, both abundance and richness were positively related to percent impervious surface (at the 2 km radius scale), highlighting the conservation value of protected areas in urban landscapes (or alternately, the potential negative aspects of agricultural landscapes). Importantly, models incorporating the influence of changing temperatures and impervious surface indicated a significant overall decline in butterfly abundance over the 20 years of this study, with an observed average decrease of 44% between the first and last sampling period. Abundance declines were noted across all investigated functional groups. For species richness, we observed a declining (but not significant) trend and no significant changes over time for richness of any functional group except univoltine species (which were declining). Butterfly community composition changed through time, but we did not find evidence of systematic biotic homogenization, perhaps because abundance declines were occurring across functional groups. Finally, at the site-level, declines in either richness or abundance occurred at five of seven locations, with the two largest locations (>300 Ha) not exhibiting declines. Our results mirror those of other long-term butterfly studies that found alarming decreases in butterfly abundance, with slower declines in species richness.