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David N Koons - One of the best experts on this subject based on the ideXlab platform.
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Shifting Vital Rate Correlations Alter Predicted Population Responses to Increasingly Variable Environments.
The American naturalist, 2019Co-Authors: David T. Iles, Robert F. Rockwell, David N KoonsAbstract:Time series of Vital Rates are often used to construct "environment-blind" stochastic population projections and calculate the elasticity of population growth to increased temporal variance in Vital Rates. Here, we show that the utility of this widely used demographic tool is greatly limited by shifts in Vital Rate correlations that occur as environmental drivers become increasingly variable. The direction and magnitude of these shifts are unpredictable without environmentally explicit models. Shifting Vital Rate correlations had the largest fitness effects on life histories with short to medium generation times, potentially hampering comparative analyses based on elasticities to Vital Rate variance for a wide range of species. Shifts in Vital Rate correlations are likely ubiquitous in increasingly variable environments, and further research should empirically evaluate the life histories for which detailed mechanistic relationships between Vital Rates and environmental drivers are required for making reliable predictions versus those for which summarized demographic data are sufficient.
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Evaluating Vital Rate contributions to greater sage‐grouse population dynamics to inform conservation
Ecosphere, 2016Co-Authors: David K. Dahlgren, Michael R. Guttery, Terry A. Messmer, Danny Caudill, Robert Dwayne Elmore, Renee Chi, David N KoonsAbstract:Species conservation efforts often use short-term studies that fail to identify the Vital Rates that contribute most to population growth. Although the greater sage-grouse (Centrocercus urophasianus; sage-grouse) is a candidate for protection under the U.S. Endangered Species Act, and is sometimes referred to as an umbrella species in the sagebrush (Artemisia spp.) biome of western North America, the failure of proposed management stRategies to focus on key Vital Rates that may contribute most to achieving population stability remains problematic for sustainable conservation. To address this dilemma, we performed both prospective and retrospective perturbation analyses of a life cycle model based on a 12-yr study that encompassed nearly all sage-grouse Vital Rates. To validate our population models, we compared estimates of annual finite population growth Rates (λ) from our female-based life cycle models to those attained from male-based lek counts. Post-fledging (i.e., after second year, second year, and juvenile) female survival parameters contributed most to past variation in λ during our study and had the greatest potential to change λ in the future, indicating these Vital Rates as important determinants of sage-grouse population dynamics. In addition, annual estimates of λ from female-based life cycle models and male-based lek data were similar, providing the most rigorous evidence to date that lek counts of males can serve as a valid index of sage-grouse population change. Our comparison of fixed and mixed statistical models for evaluating temporal variation in nest survival and initiation suggest that conservation planners use caution when evaluating short-term nesting studies and using associated fixed-effect results to develop conservation objectives. In addition, our findings indicated that greater attention should be paid to those factors affecting sage-grouse post-fledging females. Our approach demonstRates the need for more long-term studies of species Vital Rates across the life cycle. Such studies should address the decoupling of sampling variation from underlying process (co)variation in Vital Rates, identification of how such variation drives population dynamics, and how decision makers can use this information to re-direct conservation efforts to address the most limiting points in the life cycle for a given population.
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evaluating Vital Rate contributions to greater sage grouse population dynamics to inform conservation
Ecosphere, 2016Co-Authors: David K. Dahlgren, Michael R. Guttery, Terry A. Messmer, Danny Caudill, Robert Dwayne Elmore, Renee Chi, David N KoonsAbstract:Species conservation efforts often use short-term studies that fail to identify the Vital Rates that contribute most to population growth. Although the greater sage-grouse (Centrocercus urophasianus; sage-grouse) is a candidate for protection under the U.S. Endangered Species Act, and is sometimes referred to as an umbrella species in the sagebrush (Artemisia spp.) biome of western North America, the failure of proposed management stRategies to focus on key Vital Rates that may contribute most to achieving population stability remains problematic for sustainable conservation. To address this dilemma, we performed both prospective and retrospective perturbation analyses of a life cycle model based on a 12-yr study that encompassed nearly all sage-grouse Vital Rates. To validate our population models, we compared estimates of annual finite population growth Rates (λ) from our female-based life cycle models to those attained from male-based lek counts. Post-fledging (i.e., after second year, second year, and juvenile) female survival parameters contributed most to past variation in λ during our study and had the greatest potential to change λ in the future, indicating these Vital Rates as important determinants of sage-grouse population dynamics. In addition, annual estimates of λ from female-based life cycle models and male-based lek data were similar, providing the most rigorous evidence to date that lek counts of males can serve as a valid index of sage-grouse population change. Our comparison of fixed and mixed statistical models for evaluating temporal variation in nest survival and initiation suggest that conservation planners use caution when evaluating short-term nesting studies and using associated fixed-effect results to develop conservation objectives. In addition, our findings indicated that greater attention should be paid to those factors affecting sage-grouse post-fledging females. Our approach demonstRates the need for more long-term studies of species Vital Rates across the life cycle. Such studies should address the decoupling of sampling variation from underlying process (co)variation in Vital Rates, identification of how such variation drives population dynamics, and how decision makers can use this information to re-direct conservation efforts to address the most limiting points in the life cycle for a given population.
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lesser scaup population dynamics what can belearned from available data
Avian Conservation and Ecology - Écologie et conservationdes oiseaux, 2006Co-Authors: David N Koons, Stuart M Slattery, Robin M. Corcoran, David W Willey, Rodney W Brook, Jay J Rotella, Robert G. Clark, Mark L Taper, James R. LovvornAbstract:Populations of Lesser Scaup (Aythya affinis) have declined markedly in North America since the early 1980s. When considering alternatives for achieving population recovery, it would be useful to understand how the Rate of population growth is functionally related to the underlying Vital Rates and which Vital Rates affect population growth Rate the most if changed (which need not be those that influenced historical population declines). To establish a more quantitative basis for learning about life history and population dynamics of Lesser Scaup, we summarized published and unpublished estimates of Vital Rates recorded between 1934 and 2005, and developed matrix life-cycle models with these data for females breeding in the boreal forest, prairie-parklands, and both regions combined. We then used perturbation analysis to evaluate the effect of changes in a variety of Vital-Rate statistics on finite population growth Rate and abundance. Similar to Greater Scaup (Aythya marila), our modeled population growth Rate for Lesser Scaup was most sensitive to unit and proportional change in adult female survival during the breeding and non-breeding seasons, but much less so to changes in fecundity parameters. Interestingly, population growth Rate was also highly sensitive to unit and proportional changes in the mean of nesting success, duckling survival, and juvenile survival. Given the small samples of data for key aspects of the Lesser Scaup life cycle, we recommend additional research on Vital Rates that demonstRate a strong effect on population growth and size (e.g., adult survival probabilities). Our life-cycle models should be tested and regularly updated in the future to simultaneously guide science and management of Lesser Scaup populations in an adaptive context. RESUME. Les populations de Petit Fuligule (Aythya affinis) montrent un declin marque en Amerique du Nord depuis le debut des annees 1980. Lorsque l'on considere les options permettant de redresser la situation, il serait utile de comprendre la relation fonctionnelle entre le taux d'accroissement de la population et les taux vitaux, de meme que les taux vitaux qui affectent le plus ce taux d'accroissement (qui sont presumement ceux qui ont entraine le declin historique des effectifs). Afin d'etablir un fondement quantitatif pour comprendre l'histoire naturelle et la dynamique des populations de Petit Fuligule, nous avons compile les estimes (publies ou non) de taux vitaux mesures entre 1934 et 2005 et developpe a partir de ces donnees des modeles matriciels de cycle de vie pour les femelles nichant dans la foret boreale, la foret-parc des prairies et les deux regions combinees. Ensuite, nous avons utilise l'analyse des perturbations afin d'evaluer les effets de changements dans divers taux vitaux sur le taux intrinseque d'accroissement des populations et l'abondance. Comme chez le Fuligule milouinan (Aythya marila), le taux d'accroissement des populations obtenu pour le Petit Fuligule etait particulierement sensible aux variations unitaires ou proportionnelles du taux de survie des femelles adultes durant la saison de nidification ou le reste de l'annee, mais beaucoup moins sensible aux variations des parametres de fecondite. Curieusement, le taux d'accroissement des Montana State University, Canadian Wildlife Service, Institute for Wetland and Waterfowl Research, Ontario Ministry of Natural Resources, U.S. Fish and Wildlife Service, University of Wyoming Avian Conservation and Ecology Ecologie et conservation des oiseaux 1(3): 6 http://www.ace-eco.org/vol1/iss3/art6/ populations etait aussi tres sensible aux variations unitaires ou proportionnelles du succes d'eclosion moyen et des taux de survie des canetons ou des juveniles. Etant donne les faibles effectifs d'echantillons disponibles pour certains aspects-cle du cycle de vie du Petit Fuligule, nous recommandons que des travaux additionnels soient effectues sur les taux vitaux qui ont une influence majeure sur l'accroissement des populations et leur effectif (ex. taux de survie des adultes). Nos modeles de cycle de vie devraient etre testes et mis a jour regulierement afin de guider l'etude et la gestion des populations de Petit Fuligule dans un contexte adaptatif.
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lesser scaup population dynamics what can be learned from available data dynamique des populations de petit fuligule que peut on apprendre des donnees disponibles
2006Co-Authors: David N Koons, Stuart M Slattery, Robin M. Corcoran, David W Willey, Rodney W Brook, Jay J Rotella, Robert G. Clark, Mark L Taper, James R. LovvornAbstract:Populations of Lesser Scaup (Aythya affinis) have declined markedly in North America since the early 1980s. When considering alternatives for achieving population recovery, it would be useful to understand how the Rate of population growth is functionally related to the underlying Vital Rates and which Vital Rates affect population growth Rate the most if changed (which need not be those that influenced historical population declines). To establish a more quantitative basis for learning about life history and population dynamics of Lesser Scaup, we summarized published and unpublished estimates of Vital Rates recorded between 1934 and 2005, and developed matrix life-cycle models with these data for females breeding in the boreal forest, prairie-parklands, and both regions combined. We then used perturbation analysis to evaluate the effect of changes in a variety of Vital-Rate statistics on finite population growth Rate and abundance. Similar to Greater Scaup (Aythya marila), our modeled population growth Rate for Lesser Scaup was most sensitive to unit and proportional change in adult female survival during the breeding and non-breeding seasons, but much less so to changes in fecundity parameters. Interestingly, population growth Rate was also highly sensitive to unit and proportional changes in the mean of nesting success, duckling survival, and juvenile survival. Given the small samples of data for key aspects of the Lesser Scaup life cycle, we recommend additional research on Vital Rates that demonstRate a strong effect on population growth and size (e.g., adult survival probabilities). Our life-cycle models should be tested and regularly updated in the future to simultaneously guide science and management of Lesser Scaup populations in an adaptive context. RESUME. Les populations de Petit Fuligule (Aythya affinis) montrent un declin marque en Amerique du Nord depuis le debut des annees 1980. Lorsque l'on considere les options permettant de redresser la situation, il serait utile de comprendre la relation fonctionnelle entre le taux d'accroissement de la population et les taux vitaux, de meme que les taux vitaux qui affectent le plus ce taux d'accroissement (qui sont presumement ceux qui ont entraine le declin historique des effectifs). Afin d'etablir un fondement quantitatif pour comprendre l'histoire naturelle et la dynamique des populations de Petit Fuligule, nous avons compile les estimes (publies ou non) de taux vitaux mesures entre 1934 et 2005 et developpe a partir de ces donnees des modeles matriciels de cycle de vie pour les femelles nichant dans la foret boreale, la foret-parc des prairies et les deux regions combinees. Ensuite, nous avons utilise l'analyse des perturbations afin d'evaluer les effets de changements dans divers taux vitaux sur le taux intrinseque d'accroissement des populations et l'abondance. Comme chez le Fuligule milouinan (Aythya marila), le taux d'accroissement des populations obtenu pour le Petit Fuligule etait particulierement sensible aux variations unitaires ou proportionnelles du taux de survie des femelles adultes durant la saison de nidification ou le reste de l'annee, mais beaucoup moins sensible aux variations des parametres de fecondite. Curieusement, le taux d'accroissement des
Jennifer L Mortensen - One of the best experts on this subject based on the ideXlab platform.
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Population Viability and Vital Rate Sensitivity of an Endangered Avian Cooperative Breeder, the White-Breasted Thrasher (Ramphocinclus brachyurus).
PloS one, 2016Co-Authors: Jennifer L Mortensen, J. Michael ReedAbstract:Social behaviors can significantly affect population viability, and some behaviors might reduce extinction risk. We used population viability analysis to evaluate effects of past and proposed habitat loss on the White-breasted Thrasher (Ramphocinclus brachyurus), a cooperatively breeding songbird with a global population size of
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population viability and Vital Rate sensitivity of an endangered avian cooperative breeder the white breasted thrasher ramphocinclus brachyurus
PLOS ONE, 2016Co-Authors: Jennifer L Mortensen, Michael J. ReedAbstract:Social behaviors can significantly affect population viability, and some behaviors might reduce extinction risk. We used population viability analysis to evaluate effects of past and proposed habitat loss on the White-breasted Thrasher (Ramphocinclus brachyurus), a cooperatively breeding songbird with a global population size of <2000 individuals. We used an individual-based approach to build the first demographic population projection model for this endangered species, parameterizing the model with data from eight years of field study before and after habitat loss within the stronghold of the species’ distribution. The recent habitat loss resulted in an approximately 18% predicted decline in population size; this estimate was mirrored by a sepaRate assessment using occupancy data. When mortality Rates remained close to the pre-habitat loss estimate, quasi-extinction probability was low under extant habitat area, but increased with habitat loss expected after current plans for resort construction are completed. Post-habitat loss mortality Rate estimates were too high for projected populations to persist. Vital Rate sensitivity analyses indicated that population growth Rate and population persistence were most sensitive to juvenile mortality. However, observed values for adult mortality were closest to the threshold value above which populations would crash. Adult mortality, already relatively low, may have the least capacity to change compared to other Vital Rates, whereas juvenile mortality may have the most capacity for improvement. Results suggest that improving mortality estimates and determining the cause(s) of juvenile mortality should be research priorities. Despite predictions that aspects of cooperative systems may result in variation in reproduction or juvenile mortality being the most sensitive Vital Rates, adult mortality was the most sensitive in half of the demographic models of other avian cooperative breeders. Interestingly, Vital Rate sensitivity differed by model type. However, studies that explicitly modeled the species’ cooperative breeding system found reproduction to be the most sensitive Rate.
Michael J. Reed - One of the best experts on this subject based on the ideXlab platform.
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population viability and Vital Rate sensitivity of an endangered avian cooperative breeder the white breasted thrasher ramphocinclus brachyurus
PLOS ONE, 2016Co-Authors: Jennifer L Mortensen, Michael J. ReedAbstract:Social behaviors can significantly affect population viability, and some behaviors might reduce extinction risk. We used population viability analysis to evaluate effects of past and proposed habitat loss on the White-breasted Thrasher (Ramphocinclus brachyurus), a cooperatively breeding songbird with a global population size of <2000 individuals. We used an individual-based approach to build the first demographic population projection model for this endangered species, parameterizing the model with data from eight years of field study before and after habitat loss within the stronghold of the species’ distribution. The recent habitat loss resulted in an approximately 18% predicted decline in population size; this estimate was mirrored by a sepaRate assessment using occupancy data. When mortality Rates remained close to the pre-habitat loss estimate, quasi-extinction probability was low under extant habitat area, but increased with habitat loss expected after current plans for resort construction are completed. Post-habitat loss mortality Rate estimates were too high for projected populations to persist. Vital Rate sensitivity analyses indicated that population growth Rate and population persistence were most sensitive to juvenile mortality. However, observed values for adult mortality were closest to the threshold value above which populations would crash. Adult mortality, already relatively low, may have the least capacity to change compared to other Vital Rates, whereas juvenile mortality may have the most capacity for improvement. Results suggest that improving mortality estimates and determining the cause(s) of juvenile mortality should be research priorities. Despite predictions that aspects of cooperative systems may result in variation in reproduction or juvenile mortality being the most sensitive Vital Rates, adult mortality was the most sensitive in half of the demographic models of other avian cooperative breeders. Interestingly, Vital Rate sensitivity differed by model type. However, studies that explicitly modeled the species’ cooperative breeding system found reproduction to be the most sensitive Rate.
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Vital Rate sensitivity analysis as a tool for assessing management actions for the desert tortoise
Biological Conservation, 2009Co-Authors: Michael J. Reed, Nina H. Fefferman, Roy C AverillmurrayAbstract:Sensitivity analyses of population growth in desert tortoise (Gopherus agassizii) have shown no consensus on the limiting Vital Rate. More importantly, the most sensitive Vital Rate might not be the most readily manipulated by management, so it begs the question of what actions would be most effective. We compared 13 management alternatives using a Vital Rate sensitivity analysis that is valid regardless of age structure, and is sensitive to initial population size and time frame, to determine the efforts required for equivalent population growth. We evaluated three time frames, each with five initial population sizes and three initial age distributions. To achieve equivalent population growth, mortality of older females needed to be reduced less than did mortality of other age classes. Similarly, fewer adults needed to be introduced to a population to have the same effect as releasing juveniles, but differences among adult age classes were trivial. A single release (headstarting) required fewer total individuals than did annual releases to achieve the same population growth. Also, the same population growth was more easily achieved when the initial age structure was deficient of young animals. Interestingly, because small tortoises are difficult to survey, some management alternatives could result in increased population size but decreased numbers of countable individuals over short to intermediate (25 years) time frames. Our paper demonstRates an approach to determine what constitutes equivalent management actions for population growth, thus allowing managers to more directly compare expected gains toward population recovery achieved by their resource-allocation decisions.
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a Vital Rate sensitivity analysis for nonstable age distributions and short term planning
Journal of Wildlife Management, 2006Co-Authors: Nina H. Fefferman, Michael J. ReedAbstract:Abstract There are multiple approaches to sensitivity analysis used to identify the age- (or stage-) specific Rate of reproduction or survival that most affects population growth—all of which involve evaluating effects on λ, the dominant eigenvalue of the Leslie matrix. Management recommendations geneRated by these approaches can be difficult to determine, in part because results are valid only for populations with stable age distributions (i.e., the age structure is constant across years). Although these analytical approaches can identify the quickest way to increase population size to carrying capacity, they cannot identify best management options for short-term goals such as increasing population size above some critical value. We present a perturbation analysis—Vital Rate Sensitivity Analysis (VRSA)—to identify the Vital Rate that most limits population growth over any specified period by determining which Vital Rate has the greatest effect on population growth. The VRSA is effective for stable and no...
J. Michael Reed - One of the best experts on this subject based on the ideXlab platform.
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Population Viability and Vital Rate Sensitivity of an Endangered Avian Cooperative Breeder, the White-Breasted Thrasher (Ramphocinclus brachyurus).
PloS one, 2016Co-Authors: Jennifer L Mortensen, J. Michael ReedAbstract:Social behaviors can significantly affect population viability, and some behaviors might reduce extinction risk. We used population viability analysis to evaluate effects of past and proposed habitat loss on the White-breasted Thrasher (Ramphocinclus brachyurus), a cooperatively breeding songbird with a global population size of
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A Vital Rate Sensitivity Analysis for Nonstable Age Distributions and Short‐Term Planning
Journal of Wildlife Management, 2006Co-Authors: Nina H. Fefferman, J. Michael ReedAbstract:Abstract There are multiple approaches to sensitivity analysis used to identify the age- (or stage-) specific Rate of reproduction or survival that most affects population growth—all of which involve evaluating effects on λ, the dominant eigenvalue of the Leslie matrix. Management recommendations geneRated by these approaches can be difficult to determine, in part because results are valid only for populations with stable age distributions (i.e., the age structure is constant across years). Although these analytical approaches can identify the quickest way to increase population size to carrying capacity, they cannot identify best management options for short-term goals such as increasing population size above some critical value. We present a perturbation analysis—Vital Rate Sensitivity Analysis (VRSA)—to identify the Vital Rate that most limits population growth over any specified period by determining which Vital Rate has the greatest effect on population growth. The VRSA is effective for stable and no...
Ian Stirling - One of the best experts on this subject based on the ideXlab platform.
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climate change threatens polar bear populations a stochastic demographic analysis
Ecology, 2010Co-Authors: Christine M Hunter, Michael C Runge, Eric V. Regehr, Steven C. Amstrup, Hal Caswell, Ian StirlingAbstract: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 k 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 ks, as the frequency of poor ice years increased. The observed frequency of poor ice years since 1979 would imply log ks ' � 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.
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survival and breeding of polar bears in the southern beaufort sea in relation to sea ice
Journal of Animal Ecology, 2010Co-Authors: Eric V. Regehr, Steven C. Amstrup, Christine M Hunter, Hal Caswell, Ian StirlingAbstract:1. Observed and predicted declines in Arctic sea ice have raised concerns about marine mammals. In May 2008, the US Fish and Wildlife Service listed polar bears (Ursus maritimus) - one of the most ice-dependent marine mammals - as threatened under the US Endangered Species Act. 2. We evaluated the effects of sea ice conditions on Vital Rates (survival and breeding probabilities) for polar bears in the southern Beaufort Sea. Although sea ice declines in this and other regions of the polar basin have been among the greatest in the Arctic, to date population-level effects of sea ice loss on polar bears have only been identified in western Hudson Bay, near the southern limit of the species' range. 3. We estimated Vital Rates using multistate capture-recapture models that classified individuals by sex, age and reproductive category. We used multimodel inference to evaluate a range of statistical models, all of which were structurally based on the polar bear life cycle. We estimated parameters by model averaging, and developed a parametric bootstrap procedure to quantify parameter uncertainty. 4. In the most supported models, polar bear survival declined with an increasing number of days per year that waters over the continental shelf were ice free. In 2001-2003, the ice-free period was relatively short (mean 101 days) and adult female survival was high (0.96-0.99, depending on reproductive state). In 2004 and 2005, the ice-free period was longer (mean 135 days) and adult female survival was low (0.73-0.79, depending on reproductive state). Breeding Rates and cub litter survival also declined with increasing duration of the ice-free period. Confidence intervals on Vital Rate estimates were wide. 5. The effects of sea ice loss on polar bears in the southern Beaufort Sea may apply to polar bear populations in other portions of the polar basin that have similar sea ice dynamics and have experienced similar, or more severe, sea ice declines. Our findings therefore are relevant to the extinction risk facing approximately one-third of the world's polar bears.
