title: Quasi-extinction risk and population targets for the Eastern, migratory population of monarch butterflies (Danaus plexippus).
abstract: The Eastern, migratory population of monarch butterflies (Danaus plexippus), an iconic North American insect, has declined by ~80% over the last decade. The monarch's multi-generational migration between overwintering grounds in central Mexico and the summer breeding grounds in the northern U.S. and southern Canada is celebrated in all three countries and creates shared management responsibilities across North America. Here we present a novel Bayesian multivariate auto-regressive state-space model to assess quasi-extinction risk and aid in the establishment of a target population size for monarch conservation planning. We find that, given a range of plausible quasi-extinction thresholds, the population has a substantial probability of quasi-extinction, from 11-57% over 20 years, although uncertainty in these estimates is large. Exceptionally high population stochasticity, declining numbers, and a small current population size act in concert to drive this risk. An approximately 5-fold increase of the monarch population size (relative to the winter of 2014-15) is necessary to halve the current risk of quasi-extinction across all thresholds considered. Conserving the monarch migration thus requires active management to reverse population declines, and the establishment of an ambitious target population size goal to buffer against future environmentally driven variability.
authors.affiliation: Scripps Institution of Oceanography, University of California, San Diego, 9500 Gilman Drive, La Jolla CA 92093, USA.
authors.forename: Brice X
authors.initials: BX
authors.lastname: Semmens
authors.affiliation: United States Geological Survey, Geosciences and Environmental Change Science Center, Denver, CO 80225, USA.
authors.forename: Darius J
authors.initials: DJ
authors.lastname: Semmens
authors.affiliation: United States Geological Survey, Upper Midwest Environmental Sciences Center, 2630 Fanta Reed Road, La Crosse, WI 54603, USA.
authors.forename: Wayne E
authors.initials: WE
authors.lastname: Thogmartin
authors.affiliation: School of Natural Resources and the Environment and Udall Center for Studies in Public Policy, The University of Arizona, Tucson, AZ 85721, USA.
authors.forename: Ruscena
authors.initials: R
authors.lastname: Wiederholt
authors.affiliation: School of Natural Resources and the Environment and Udall Center for Studies in Public Policy, The University of Arizona, Tucson, AZ 85721, USA.
authors.forename: Laura
authors.initials: L
authors.lastname: López-Hoffman
authors.affiliation: United States Geological Survey, Geosciences and Environmental Change Science Center, Denver, CO 80225, USA.
authors.forename: Jay E
authors.initials: JE
authors.lastname: Diffendorfer
authors.affiliation: Department of Ecology, Evolution, and Organismal Biology, Iowa State University, Ames, IA 50011, USA.
authors.forename: John M
authors.initials: JM
authors.lastname: Pleasants
authors.affiliation: Department of Fisheries, Wildlife and Conservation Biology, University of Minnesota, St Paul, MN, USA.
authors.forename: Karen S
authors.initials: KS
authors.lastname: Oberhauser
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Kansas, Lawrence, KS, USA.
authors.forename: Orley R
authors.initials: OR
authors.lastname: Taylor
mesh_terms: D025041:Animal Migration; D000818:Animals; D001499:Bayes Theorem; D002080:Butterflies / Q000502:physiology*; D003247:Conservation of Natural Resources; D056727:Endangered Species; D053476:Extinction, Biological; D015999:Multivariate Analysis; D009656:North America; D011156:Population Density; D011157:Population Dynamics; D012306:Risk