Opposing global change drivers counterbalance trends in breeding North American monarch butterflies

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Author(s)Crossley, Michael S.
Author(s)Meehan, Timothy D.
Author(s)Moran, Matthew D.
Author(s)Glassberg, Jeffrey
Author(s)Snyder, William E.
Author(s)Davis, Andrew K.
Date Accessioned2022-06-28T19:15:26Z
Date Available2022-06-28T19:15:26Z
Publication Date2022-06-10
DescriptionThis article was originally published in Global Change Biology. The version of record is available at: https://doi.org/10.1111/gcb.16282en_US
AbstractMany insects are in clear decline, with monarch butterflies (Danaus plexippus) drawing particular attention as a flagship species. It is well documented that, among migratory populations, numbers of overwintering monarchs have been falling across several decades, but trends among breeding monarchs are less clear. Here, we compile >135,000 monarch observations between 1993 and 2018 from the North American Butterfly Association's annual butterfly count to examine spatiotemporal patterns and potential drivers of adult monarch relative abundance trends across the entire breeding range in eastern and western North America. While the data revealed declines at some sites, particularly the US Northeast and parts of the Midwest, numbers in other areas, notably the US Southeast and Northwest, were unchanged or increasing, yielding a slightly positive overall trend across the species range. Negative impacts of agricultural glyphosate use appeared to be counterbalanced by positive effects of annual temperature, particularly in the US Midwest. Overall, our results suggest that population growth in summer is compensating for losses during the winter and that changing environmental variables have offsetting effects on mortality and/or reproduction. We suggest that density-dependent reproductive compensation when lower numbers arrive each spring is currently able to maintain relatively stable breeding monarch numbers. However, we caution against complacency since accelerating climate change may bring growing threats. In addition, increases of summer monarchs in some regions, especially in California and in the south, may reflect replacement of migratory with resident populations. Nonetheless, it is perhaps reassuring that ubiquitous downward trends in summer monarch abundance are not evident.en_US
SponsorWe acknowledge funding from USDA-NIFA-OREI 2015–51,300-24,155, USDA-NIFA-SCRI 2015–51,181-24,292, and USDA-Hatch DEL00774.en_US
CitationCrossley, M. S., Meehan, T. D., Moran, M. D., Glassberg, J., Snyder, W. E., & Davis, A. K. (2022). Opposing global change drivers counterbalance trends in breeding North American monarch butterflies. Global Change Biology, 00, 1– 10. https://doi.org/10.1111/gcb.16282en_US
ISSN1365-2486
URLhttps://udspace.udel.edu/handle/19716/31032
Languageen_USen_US
PublisherGlobal Change Biologyen_US
Keywordsconservation effortsen_US
Keywordsdeclineen_US
Keywordsglyphosateen_US
Keywordsmonarch butterflyen_US
Keywordspopulation trendsen_US
TitleOpposing global change drivers counterbalance trends in breeding North American monarch butterfliesen_US
TypeArticleen_US
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