Understanding a migratory species in a changing world: climatic effects and demographic declines in the western monarch revealed by four decades of intensive monitoring

Espeset, Anne; Harrison, Joshua G.; Shapiro, Arthur M.; Nice, Chris C.; Thorne, James H.; Waetjen, David P.; Fordyce, James A.; Forister, Matthew L.

doi:10.1007/s00442-016-3600-y

Cited by 49 publications

(79 citation statements)

References 47 publications

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“…Similarly, the importance of overwintering habitat loss in the PLSR analysis corroborates speculation by Espeset et al. (), who proposed the overwintering stage as an important driver of monarch populations because, at a set of breeding sites in central California, declines in adult monarch abundance were stronger in spring than summer. Espeset et al.…”

Section: Discussionsupporting

confidence: 86%

“…, Stevens and Frey , Espeset et al. ). These past analyses, as well as naïve interpretation of our MRMI, could be interpreted as evidence that climate is the primary driver of western monarch populations.…”

Section: Discussionmentioning

confidence: 99%

“…After accounting for overall negative population trends, breeding season monarchs in central California from 1972 to 2014 tended to be more abundant in years with warmer and wetter springs (Espeset et al. ). Western monarch abundance is also negatively correlated with drought (Stevens and Frey ).…”

Section: Introductionmentioning

confidence: 99%

“…Espeset et al. , Malcolm ). Similar to the West, higher precipitation in the spring led to larger eastern monarch populations by the end of the breeding season (Zipkin et al.…”

Section: Introductionmentioning

confidence: 99%

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Why are monarch butterflies declining in the West? Understanding the importance of multiple correlated drivers

Crone

Pelton

Brown

et al. 2019

Ecological Applications

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Understanding the factors associated with declines of at‐risk species is an important first step in setting management and recovery targets. This step can be challenging when multiple aspects of climate and land use are changing simultaneously, and any or all could be contributing to population declines. We analyzed population trends of monarch butterflies in western North America in relation to likely environmental drivers. Unlike the larger eastern monarch population, past analyses of western monarchs have only evaluated the importance of climate (i.e., not land use) factors as drivers of abundance. We used partial least squares regression (PLSR) to evaluate the potential importance of changes in land use and climate variables. Trends in western monarch abundance were more strongly associated with land use variables than climate variables. Conclusions about importance of climate and land use variables were robust to changes in PLSR model structure. However, individual variables were too collinear to unambiguously separate their effects. We compared these conclusions to the more widely used technique of multiple regression, followed by multi‐model inference (MRMI). Naïve interpretation of MRMI results could be misleading, if collinearity were not taken into account. MRMI was also highly sensitive to variation in model construction. Our results suggest a two‐pronged approach to monarch conservation, specifically, starting efforts now to restore habitat, while also using experiments to more clearly delineate separate effects of climate and land use factors. They also demonstrate the utility of PLSR, a technique that is growing in use but is still relatively under‐appreciated in conservation biology.

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Section: Discussionsupporting

confidence: 86%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

“…Espeset et al. , Malcolm ). Similar to the West, higher precipitation in the spring led to larger eastern monarch populations by the end of the breeding season (Zipkin et al.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Why are monarch butterflies declining in the West? Understanding the importance of multiple correlated drivers

Crone

Pelton

Brown

et al. 2019

Ecological Applications

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“…The past two years have seen tremendous media attention and scientific discourse on the population decline of the monarch butterfly (Wagner et al , Berenbaum , Rubinoff , Shapiro , Pleasants et al ). While there has been consistency in some of the analyses, other research and interpretations has called into question the extent to which we truly understand fluctuations in monarch population sizes, especially given the complex annual migratory cycle (Dyer and Forister , Espeset et al , Ries et al ). We hope that our analysis linking the annual population steps has shed light on this important conservation issue, and moreover that our approach will be useful in understanding the similar challenges faced by many long‐distance migrants (Wilcove and Wikelski ).…”

Section: Discussionmentioning

confidence: 99%

Linking the continental migratory cycle of the monarch butterfly to understand its population decline

Inamine

Ellner

Springer³

et al. 2016

Oikos

135

160

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Threats to several of the world's great animal migrations necessitate a research agenda focused on identifying drivers of their population dynamics. The monarch butterfly is an iconic species whose continental migratory population in eastern North America has been declining precipitously. Recent analyses have linked the monarch decline to reduced abundance of milkweed host plants in the USA caused by increased use of genetically modified herbicide‐resistant crops. To identify the most sensitive stages in the monarch's annual multi‐generational migration, and to test the milkweed limitation hypothesis, we analyzed 22 years of citizen science records from four monitoring programs across North America. We analyzed the relationships between butterfly population indices at successive stages of the annual migratory cycle to assess demographic connections and to address the roles of migrant population size versus temporal trends that reflect changes in habitat or resource quality. We find a sharp annual population decline in the first breeding generation in the southern USA, driven by the progressively smaller numbers of spring migrants from the overwintering grounds in Mexico. Monarch populations then build regionally during the summer generations. Contrary to the milkweed limitation hypothesis, we did not find statistically significant temporal trends in stage‐to‐stage population relationships in the mid‐western or northeastern USA. In contrast, there are statistically significant negative temporal trends at the overwintering grounds in Mexico, suggesting that monarch success during the fall migration and re‐establishment strongly contributes to the butterfly decline. Lack of milkweed, the only host plant for monarch butterfly caterpillars, is unlikely to be driving the monarch's population decline. Conservation efforts therefore require additional focus on the later phases in the monarch's annual migratory cycle. We hypothesize that lack of nectar sources, habitat fragmentation, continued degradation at the overwintering sites, or other threats to successful fall migration are critical limiting factors for declining monarchs.

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Using community science to map western monarch butterflies (Danaus plexippus) in spring

Erickson,

Jason,

Machiorlete

et al. 2023

Ecology and Evolution

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Migratory animals follow seasonal cycles comprising linked phases often with different habitat requirements and demographic processes. Conservation of migratory species therefore must consider the full seasonal cycle to identify points limiting population viability. For western monarch butterflies, which have experienced significant declines, early spring is considered a critical period in the annual population cycle. However, records of western monarchs in early spring, when overall abundance is lowest, have historically been extremely limited. We used a community science initiative, the Western Monarch Mystery Challenge, to collect data on monarch distribution throughout the western United States between February 14th and April 22nd over 3 years. Using data from the Western Monarch Mystery Challenge and iNaturalist, we identified potential breeding habitat for western monarchs in early spring that spanned a large geographic area and several ecoregions. We observed monarchs in early spring that likely eclosed in the current year, suggesting that population expansion from overwintering sites reflects both movement and population growth. The number of records of western monarchs from early spring was higher during the Mystery Challenge (33.0/year) than earlier years (5.1/year). This study demonstrates the potential for and limitations of community science to increase our understanding of species at points in the life cycle when they are rare.

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Understanding a migratory species in a changing world: climatic effects and demographic declines in the western monarch revealed by four decades of intensive monitoring

Cited by 49 publications

References 47 publications

Why are monarch butterflies declining in the West? Understanding the importance of multiple correlated drivers

Why are monarch butterflies declining in the West? Understanding the importance of multiple correlated drivers

Linking the continental migratory cycle of the monarch butterfly to understand its population decline

Using community science to map western monarch butterflies (Danaus plexippus) in spring

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