Changes in climate drive recent monarch butterfly dynamics

Zylstra, Erin R.; Ries, Leslie; Neupane, Naresh; Saunders, Sarah P.; Ramírez, M. Isabel; Rendón-Salinas, Eduardo; Oberhauser, Karen S.; Farr, Matthew; Zipkin, Elise F.

doi:10.1038/s41559-021-01504-1

Cited by 57 publications

(101 citation statements)

References 71 publications

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“…Recent analyses indicate that changing climate is driving increases and decreases in overall butterfly numbers across North America (Crossley et al, 2021; Forister et al, 2021), and, there is evidence that temperature and precipitation in North America is indirectly and positively impacting abundances of overwintering monarchs, via positive effects on breeding monarch population size (Zylstra et al, 2021). Such counterbalancing effects of seasonal temperature and precipitation appear to be common in butterflies (Davies, 2019; Konvicka et al, 2021; Roland & Matter, 2016).…”

Section: Discussionmentioning

confidence: 99%

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

Crossley

Meehan

Moran

et al. 2022

Global Change Biology

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Many 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.

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Section: Discussionmentioning

confidence: 99%

“…As such, determining the impact of glyphosate use on monarch abundance was a priority for us here. In addition, summer climate variables are also known to influence relative abundance of monarchs (Zylstra et al, 2021), and our analyses also incorporated such data.…”

Section: Explaining Spatiotemporal Variation In Relative Abundancementioning

confidence: 99%

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

Crossley

Meehan

Moran

et al. 2022

Global Change Biology

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“…Despite significant academic and public energy focused on understanding and reversing this, the exact cause of this decline is still a matter of debate. Multiple factors have been proposed to underlie the monarch’s decline, including a decrease in the abundance of the monarch’s food source (primarily a single species of milkweed – common milkweed), reduced abundance or quality of nectar plants, climate change, and destruction of their overwintering site (Haan and Landis 2019; Boyle, Dalgleish, and Puzey 2019; Inamine et al 2016; Zylstra et al 2021).…”

Section: Introductionmentioning

confidence: 99%

Temporal matches and mismatches between monarch butterfly and milkweed population changes over the past 12,000 years

Boyle

Strickler

Twyford

et al. 2022

Preprint

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In intimate ecological interactions, the interdependency of species may result in correlated demographic histories. For species of conservation concern, understanding the long-term dynamics of such interactions may shed light on the drivers of population decline. Here we address the demographic history of the monarch butterfly, Danaus plexippus, and its dominant host plant, the common milkweed Asclepias syriaca, using broad-scale sampling and genomic inference. Because genetic resources for milkweed have lagged behind those for monarchs, we first release a chromosome-level genome assembly and annotation for common milkweed. Next, we show that despite its enormous geographic range across eastern North America, A. syriaca is best characterized as a single, roughly panmictic population. Using Approximate Bayesian Computation via Random Forests (ABC-RF), a machine learning method for reconstructing demographic histories, we show that both monarchs and milkweed experienced concurrent range expansion during the most recent recession of North American glaciers ∼12,000 years ago. Our data identify an expansion of milkweed during the large-scale clearing of eastern forests (∼200 years ago) but was inconclusive as to expansion or contraction of the monarch butterfly population during this time. Finally, our results indicate that neither species experienced a population contraction over the past 75 years. Thus, the well-documented decline of monarch abundance over the past 40 years is not visible in our genomic dataset, reflecting a possible mismatch of the overwintering census population to effective population size in this species.

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“…). [7–10]. Many monarch conservation strategies have been suggested, from changes in agricultural practices to the planting of milkweeds by individuals in gardens and yards [11].…”

Section: Introductionmentioning

confidence: 99%

“…The causes of these declines are complex and region-specific, but proposed hypotheses implicate climate change, the loss of overwintering habitat, natural enemies, and pesticides, especially herbicides affecting the abundance of native milkweeds ( Asclepias spp.) (Crone et al, 2019; Stenoien et al, 2018; Thogmartin et al, 2017b; Zylstra et al, 2021). Many monarch conservation strategies have been suggested, from changes in agricultural practices to the planting of milkweeds by individuals in gardens and yards (Thogmartin et al, 2017a).…”

Section: Introductionmentioning

confidence: 99%

Milkweed plants bought at nurseries may expose monarch caterpillars to harmful pesticide residues

Halsch

Hoyle

Code

et al. 2022

Preprint

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The decline of monarch butterflies in both the eastern and western United States has garnered widespread public interest. Planting milkweed has been promoted as one action that individuals can take, but very little is known with respect to potential pesticide contamination of store-bought milkweeds during the process of production and transport to market. In this study, we collected 235 milkweed leaf samples from 33 retail nurseries across the US to screen for pesticides. Across all samples, we detected 61 different pesticides with an average of 12.2 compounds per leaf. While most of the compounds have unknown effects on caterpillars, 48 samples contained a pesticide at a concentration that exceeds a published lepidopteran LD50 and 89 contained a pesticide above a concentration shown to have a sub-lethal effect for a monarch. We detected only modest effects of store size and milkweed species; however, plants with labels advertising their value for wildlife were more likely to contain pesticides at concentrations known to have negative effects on monarchs. These results demonstrate the extensiveness of pesticide exposure within nursery milkweeds and the potential impacts on monarch caterpillars and other insects consuming store-bought plants.

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Changes in climate drive recent monarch butterfly dynamics

Cited by 57 publications

References 71 publications

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

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

Temporal matches and mismatches between monarch butterfly and milkweed population changes over the past 12,000 years

Milkweed plants bought at nurseries may expose monarch caterpillars to harmful pesticide residues

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