Density estimates of monarch butterflies overwintering in central Mexico
Author
Thogmartin, Wayne E.Diffendorfer, Jay E.
López-Hoffman, Laura
Oberhauser, Karen
Pleasants, John
Semmens, Brice X.
Semmens, Darius
Taylor, Orley R.
Wiederholt, Ruscena
Affiliation
Univ Arizona, Sch Nat Resources & EnvironmIssue Date
2017-04-26Keywords
Mixture distributionMonarch butterfly
Uncertainty modeling
Danaus plexxipus
Density estimation
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PEERJ INCCitation
Density estimates of monarch butterflies overwintering in central Mexico 2017, 5:e3221 PeerJJournal
PeerJRights
© 2017 Thogmartin et al. This is an open access article distributed under the terms of the Creative Commons Attribution License.Collection Information
This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at repository@u.library.arizona.edu.Abstract
Given the rapid population decline and recent petition for listing of the monarch butterfly (Danaus plexippus L.) under the Endangered Species Act, an accurate estimate of the Eastern, migratory population size is needed. Because of difficulty in counting individual monarchs, the number of hectares occupied by monarchs in the overwintering area is commonly used as a proxy for population size, which is then multiplied by the density of individuals per hectare to estimate population size. There is, however, considerable variation in published estimates of overwintering density, ranging from 6.9-60.9 million ha(-1). We develop a probability distribution for overwinter density of monarch butterflies from six published density estimates. The mean density among the mixture of the six published estimates was similar to 27.9 million butterflies ha(-1) (95% CI [2.4-80.7] million ha(-1)); the mixture distribution is approximately log-normal, and as such is better represented by the median (21.1 million butterflies ha(-1)). Based upon assumptions regarding the number of milkweed needed to support monarchs, the amount of milkweed (Asciepias spp.) lost (0.86 billion stems) in the northern US plus the amount of milkweed remaining (1.34 billion stems), we estimate >1.8 billion stems is needed to return monarchs to an average population size of 6 ha. Considerable uncertainty exists in this required amount of milkweed because of the considerable uncertainty occurring in overwinter density estimates. Nevertheless, the estimate is on the same order as other published estimates, The studies included in our synthesis differ substantially by year, location, method, and measures of precision. A better understanding of the factors influencing overwintering density across space and time would be valuable for increasing the precision of conservation recommendations.ISSN
2167-8359PubMed ID
28462031Version
Final published versionSponsors
John Wesley Powell Center for Analysis and Synthesis of the United States Geological SurveyAdditional Links
https://peerj.com/articles/3221/ae974a485f413a2113503eed53cd6c53
10.7717/peerj.3221
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