Butterfly declines in protected areas of Illinois: Assessing the influence of two decades of climate and landscape change

Abstract

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 used mixed models and PERMANOVA to evaluate trends in butterfly abundance, richness, and composition while also evaluating the effects of temperature and land use. Overall butterfly richness, but not abundance, increased in warmer years. Surprisingly, richness also was 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 agriculture). Precipitation had a significant and variable influence through time on overall butterfly abundance and abundance of resident species, larval host plant specialists, and univoltine species. Importantly, models incorporating the influence of changing temperature, precipitation, and impervious surface indicated a significant overall decline in both butterfly abundance and species richness, with an estimated abundance decrease of 3.8%/year and richness decrease of 1.6%/year (52.5% and 27.1% cumulatively from 1999 to 2018). Abundance and richness declines were also noted across all investigated functional groups except non-resident (migratory) species. Butterfly community composition changed through time, but we did not find evidence of systematic biotic homogenization, perhaps because declines were occurring in nearly all functional groups. Finally, at the site-level, declines in either richness or abundance occurred at five of seven locations, with only the two largest locations (>300 Ha) not exhibiting declines. Our results mirror those of other long-term butterfly studies predominantly in Europe and North America that have found associations of butterflies with climate variables and general declines in butterfly richness and abundance.

South European mountain butterflies at a high risk from land abandonment and amplified effects of climate change

“…The decline found in Picos de Europa butterfly abundance in the last 9 years is in line with previous studies from elsewhere (Brereton et al, 2019; Fox et al, 2023; Melero et al, 2016; Van Swaay et al, 2017, 2020; Wepprich et al, 2019), confirming a global butterfly declining trend, even in well‐established protected areas, which are nonetheless affected by global change drivers (Colom et al, 2019; Kuckerov et al, 2021). However, the annual 5.7% decline in abundance found doubles the maximum annual decline rates found in other studies, which range from −2.6% to −0.8% (see tab.…”

“…T A B L E 2 TAOc (community preference for open/closed habitats), STIc (community temperature index) and SPIc (community precipitation index) over time on each transect. nonetheless affected by global change drivers (Colom et al, 2019;Kuckerov et al, 2021). However, the annual 5.7% decline in abundance found doubles the maximum annual decline rates found in other studies, which range from À2.6% to À0.8% (see tab.…”

Disproportionate declines of formerly abundant species underlie insect loss

“…However, although declines in insect abundance and biomass have been shown in large-scale studies and syntheses 2 , 5 , 6 , trends in other biodiversity metrics have been less clear. Species richness, for example, has been found to decline along with abundance in some large studies 5 , 14 , whereas in other studies, insect richness was reported to be stable 6 , 7 .…”

“…Here we examine the multidimensional nature of biodiversity trends in assemblages of terrestrial insects, arachnids (spiders and mites) and Entognatha (springtails and allies)—hereafter described collectively as ‘insects’, for brevity—during the past decades using a large compilation of insect surveys through time 18 . Although previous work has examined some of these multifaceted patterns for subsets of taxa (for example, butterflies 14 or hoverflies 16 ), locations 6 , 7 and/or habitat types 19 , our synthetic approach allows us to assess the prevailing trends in multiple biodiversity metrics from the openly available long-term insect assemblage data across locations, taxa and habitats. Our focus here is on terrestrial insects only, because two recent studies from Europe 20 and North America 21 have used extensive data compilations to assess changes to the diversity of freshwater invertebrates.…”

Insecticides, more than herbicides, land use, and climate, are associated with declines in butterfly species richness and abundance in the American Midwest

“…For butterflies, declines have been widely reported, including in the UK, Netherlands, and grassland habitat across Europe [4]. In the United States, widespread declines have been reported, including the Midwest [5], with similar results using independent data in Ohio [6], and Illinois [7], but with the starkest declines in the Western US [8,9]. Exceptions to the general pattern of insect decline include no trends for aquatic insects globally, but this was controversial [10].…”