Publication Date:
2022-05-25
Description:
Author 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.
Description:
The 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.
Description:
We 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.
Keywords:
Climate change
;
Demography
;
IPCC
;
LTRE analysis
;
Matrix population models
;
Polar bear
;
Sea ice
;
Stochastic growth rate
;
Stochastic models
;
Ursus maritimus
Repository Name:
Woods Hole Open Access Server
Type:
Article
Format:
application/pdf
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