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dc.contributor.authorHunter, Christine M.
dc.contributor.authorCaswell, Hal
dc.contributor.authorRunge, Michael C.
dc.contributor.authorRegehr, Eric V.
dc.contributor.authorAmstrup, Steve C.
dc.contributor.authorStirling, Ian
dc.date.accessioned2011-07-14T15:42:46Z
dc.date.available2011-07-14T15:42:46Z
dc.date.issued2010-10
dc.identifier.citationEcology 91 (2010): 2883–2897en_US
dc.identifier.urihttp://hdl.handle.net/1912/4685
dc.descriptionAuthor Posting. © Ecological Society of America, 2010. This article is posted here by permission of Ecological Society of America for personal use, not for redistribution. The definitive version was published in Ecology 91 (2010): 2883–2897, doi:10.1890/09-1641.1.en_US
dc.description.abstractThe polar bear (Ursus maritimus) depends on sea ice for feeding, breeding, and movement. Significant reductions in Arctic sea ice are forecast to continue because of climate warming. We evaluated the impacts of climate change on polar bears in the southern Beaufort Sea by means of a demographic analysis, combining deterministic, stochastic, environment-dependent matrix population models with forecasts of future sea ice conditions from IPCC general circulation models (GCMs). The matrix population models classified individuals by age and breeding status; mothers and dependent cubs were treated as units. Parameter estimates were obtained from a capture–recapture study conducted from 2001 to 2006. Candidate statistical models allowed vital rates to vary with time and as functions of a sea ice covariate. Model averaging was used to produce the vital rate estimates, and a parametric bootstrap procedure was used to quantify model selection and parameter estimation uncertainty. Deterministic models projected population growth in years with more extensive ice coverage (2001–2003) and population decline in years with less ice coverage (2004–2005). LTRE (life table response experiment) analysis showed that the reduction in λ in years with low sea ice was due primarily to reduced adult female survival, and secondarily to reduced breeding. A stochastic model with two environmental states, good and poor sea ice conditions, projected a declining stochastic growth rate, log λs, as the frequency of poor ice years increased. The observed frequency of poor ice years since 1979 would imply log λs ≈ − 0.01, which agrees with available (albeit crude) observations of population size. The stochastic model was linked to a set of 10 GCMs compiled by the IPCC; the models were chosen for their ability to reproduce historical observations of sea ice and were forced with “business as usual” (A1B) greenhouse gas emissions. The resulting stochastic population projections showed drastic declines in the polar bear population by the end of the 21st century. These projections were instrumental in the decision to list the polar bear as a threatened species under the U.S. Endangered Species Act.en_US
dc.description.sponsorshipWe acknowledge primary funding for model development and analysis from the U.S. Geological Survey and additional funding from the National Science Foundation (DEB-0343820 and DEB-0816514), NOAA, the Ocean Life Institute and the Arctic Research Initiative at WHOI, and the Institute of Arctic Biology at the University of Alaska–Fairbanks. Funding for the capture–recapture effort in 2001–2006 was provided by the U.S. Geological Survey, the Canadian Wildlife Service, the Department of Environment and Natural Resources of the Government of the Northwest Territories, and the Polar Continental Shelf Project, Ottawa, Canada.en_US
dc.format.mimetypeapplication/pdf
dc.language.isoen_USen_US
dc.publisherEcological Society of Americaen_US
dc.relation.urihttp://dx.doi.org/10.1890/09-1641.1
dc.subjectClimate changeen_US
dc.subjectDemographyen_US
dc.subjectIPCCen_US
dc.subjectLTRE analysisen_US
dc.subjectMatrix population modelsen_US
dc.subjectPolar bearen_US
dc.subjectSea iceen_US
dc.subjectStochastic growth rateen_US
dc.subjectStochastic modelsen_US
dc.subjectUrsus maritimusen_US
dc.titleClimate change threatens polar bear populations : a stochastic demographic analysisen_US
dc.typeArticleen_US
dc.identifier.doi10.1890/09-1641.1


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