A polar bear paleogenome reveals extensive ancient gene flow from polar bears into brown bears

Polar bears (Ursus maritimus) and brown bears (Ursus arctos) are sister species possessing distinct physiological and behavioural adaptations that evolved over the last 500,000 years. However, comparative and population genomics analyses have revealed that several extant and extinct brown bear populations have relatively recent polar bear ancestry, probably as the result of geographically localized instances of gene flow from polar bears into brown bears. Here, we generate and analyse an approximate 20X paleogenome from an approximately 100,000-year-old polar bear that reveals a massive prehistoric admixture event, which is evident in the genomes of all living brown bears. This ancient admixture event was not visible from genomic data derived from living polar bears. Like more recent events, this massive admixture event mainly involved unidirectional gene flow from polar bears into brown bears and occurred as climate changes caused overlap in the ranges of the two species. These findings highlight the complex reticulate paths that evolution can take within a regime of radically shifting climate.

Influence of sea ice dynamics on population energetics of Western Hudson Bay polar bears

The Arctic marine ecosystem has experienced extensive changes in sea ice dynamics, with significant effects on ice-dependent species such as polar bears (Ursus maritimus). We used annual estimates of the numbers of bears onshore in the core summering area, age/sex structure and body condition data to estimate population energy density and storage energy in Western Hudson Bay polar bears from 1985 to 2018. We examined intra-population variation in energetic patterns, temporal energetic trends and the relationship between population energetics and sea ice conditions. Energy metrics for most demographic classes declined over time in relation to earlier sea ice breakup, most significantly for solitary adult females and subadult males, suggesting their greater vulnerability to nutritional stress than other age/sex classes. Temporal declines in population energy metrics were related to earlier breakup and longer lagged open-water periods, suggesting multi-year effects of sea ice decline. The length of the open-water period ranged from 102 to 166 days and increased significantly by 9.9 days/decade over the study period. Total population energy density and storage energy were significantly lower when sea ice breakup occurred earlier and the lagged open-water period was longer. At the earliest breakup and a lagged open-water period of 180 days, population energy density was predicted to be 33% lower than our minimum estimated energy density and population storage energy was predicted to be 40% lower than the minimum estimated storage energy. Consequently, over the study, the total population energy density declined by 53% (mean: 3668 ± 386 MJ kg-1/decade) and total population storage energy declined by 56% (mean: 435900 ± 46770 MJ/decade). This study provides insights into ecological mechanisms linking population responses to sea ice decline and highlights the significance of maintaining long-term research programs.

Variance in lifetime reproductive success of male polar bears

Despite the important role that population density plays in ecological and evolutionary processes, studies of solitary species that occur at low densities remain scarce. In the context of mating systems, density is expected to influence the ability of males to find and monopolize mates, in turn, influencing variance in lifetime mating/reproductive success and the opportunity for selection. Herein, we investigate variance in male lifetime mating success (LMS), lifetime reproductive success (LRS), and the mating system of a sexually dimorphic carnivore that occurs at low densities, the polar bear (Ursus maritimus). Across 17 cohorts, born from 1975 to 1991, male LMS ranged from 0 to10 mates and LRS from 0 to 14 cubs; 40% of known-age males were not known to have reproduced. The opportunity for sexual selection (Is = 1.66, range = 0.60–4.99) and selection (I = 1.76, range: 0.65–4.89) were low compared to species with similar levels of sexual size dimorphism. Skew in male LRS was also low but significant for most cohorts indicating nonrandom reproductive success. Age-specific reproductive success was biased toward males from 11 to 17 years of age, with variation in fecundity (54%) but not longevity (10%) playing an important role in male reproduction. Our results support a growing body of evidence that suggests that male-biased size dimorphism and polygynous mating systems need not be associated with high variance in male mating and/or reproductive success.

Corrigendum: Internet Blogs, Polar Bears, and Climate-Change Denial by Proxy

[This corrects the article DOI: 10.1093/biosci/bix133.].

Internet Blogs, Polar Bears, and Climate-Change Denial by Proxy

Increasing surface temperatures, Arctic sea-ice loss, and other evidence of anthropogenic global warming (AGW) are acknowledged by every major scientific organization in the world. However, there is a wide gap between this broad scientific consensus and public opinion. Internet blogs have strongly contributed to this consensus gap by fomenting misunderstandings of AGW causes and consequences. Polar bears (Ursus maritimus) have become a "poster species" for AGW, making them a target of those denying AGW evidence. Here, focusing on Arctic sea ice and polar bears, we show that blogs that deny or downplay AGW disregard the overwhelming scientific evidence of Arctic sea-ice loss and polar bear vulnerability. By denying the impacts of AGW on polar bears, bloggers aim to cast doubt on other established ecological consequences of AGW, aggravating the consensus gap. To counter misinformation and reduce this gap, scientists should directly engage the public in the media and blogosphere.

Spring fasting behavior in a marine apex predator provides an index of ecosystem productivity

The effects of declining Arctic sea ice on local ecosystem productivity are not well understood but have been shown to vary inter-specifically, spatially, and temporally. Because marine mammals occupy upper trophic levels in Arctic food webs, they may be useful indicators for understanding variation in ecosystem productivity. Polar bears (Ursus maritimus) are apex predators that primarily consume benthic and pelagic-feeding ice-associated seals. As such, their productivity integrates sea ice conditions and the ecosystem supporting them. Declining sea ice availability has been linked to negative population effects for polar bears but does not fully explain observed population changes. We examined relationships between spring foraging success of polar bears and sea ice conditions, prey productivity, and general patterns of ecosystem productivity in the Beaufort and Chukchi Seas (CSs). Fasting status (≥7 days) was estimated using serum urea and creatinine levels of 1,448 samples collected from 1,177 adult and subadult bears across three subpopulations. Fasting increased in the Beaufort Sea between 1983-1999 and 2000-2016 and was related to an index of ringed seal body condition. This change was concurrent with declines in body condition of polar bears and observed changes in the diet, condition and/or reproduction of four other vertebrate consumers within the food chain. In contrast, fasting declined in CS polar bears between periods and was less common than in the two Beaufort Sea subpopulations consistent with studies demonstrating higher primary productivity and maintenance or improved body condition in polar bears, ringed seals, and bearded seals despite recent sea ice loss in this region. Consistency between regional and temporal variation in spring polar bear fasting and food web productivity suggests that polar bears may be a useful indicator species. Furthermore, our results suggest that spatial and temporal ecological variation is important in affecting upper trophic-level productivity in these marine ecosystems.

Demography of an apex predator at the edge of its range: impacts of changing sea ice on polar bears in Hudson Bay

Changes in the abundance and distribution of wildlife populations are common consequences of historic and contemporary climate change. Some Arctic marine mammals, such as the polar bear (Ursus maritimus), may be particularly vulnerable to such changes due to the loss of Arctic sea ice. We evaluated the impacts of environmental variation on demographic rates for the Western Hudson Bay (WH), polar bear subpopulation from 1984 to 2011 using live-recapture and dead-recovery data in a Bayesian implementation of multistate capture-recapture models. We found that survival of female polar bears was related to the annual timing of sea ice break-up and formation. Using estimated vital rates (e.g., survival and reproduction) in matrix projection models, we calculated the growth rate of the WH subpopulation and projected population responses under different environmental scenarios while accounting for parametric uncertainty, temporal variation, and demographic stochasticity. Our analysis suggested a long-term decline in the number of bears from 1185 (95% Bayesian credible interval [BCI] = 993-1411) in 1987 to 806 (95% BCI = 653-984) in 2011. In the last 10 yr of the study, the number of bears appeared stable due to temporary stability in sea ice conditions (mean population growth rate for the period 2001-2010 = 1.02, 95% BCI = 0.98-1.06). Looking forward, we estimated long-term growth rates for the WH subpopulation of ~1.02 (95% BCI = 1.00-1.05) and 0.97 (95% BCI = 0.92-1.01) under hypothetical high and low sea ice conditions, respectively. Our findings support previous evidence for a demographic linkage between sea ice conditions and polar bear population dynamics. Furthermore, we present a robust framework for sensitivity analysis with respect to continued climate change (e.g., to inform scenario planning) and for evaluating the combined effects of climate change and management actions on the status of wildlife populations.

Genomic evidence of geographically widespread effect of gene flow from polar bears into brown bears

Polar bears are an arctic, marine adapted species that is closely related to brown bears. Genome analyses have shown that polar bears are distinct and genetically homogeneous in comparison to brown bears. However, these analyses have also revealed a remarkable episode of polar bear gene flow into the population of brown bears that colonized the Admiralty, Baranof and Chichagof islands (ABC islands) of Alaska. Here, we present an analysis of data from a large panel of polar bear and brown bear genomes that includes brown bears from the ABC islands, the Alaskan mainland and Europe. Our results provide clear evidence that gene flow between the two species had a geographically wide impact, with polar bear DNA found within the genomes of brown bears living both on the ABC islands and in the Alaskan mainland. Intriguingly, while brown bear genomes contain up to 8.8% polar bear ancestry, polar bear genomes appear to be devoid of brown bear ancestry, suggesting the presence of a barrier to gene flow in that direction.

Implications of the circumpolar genetic structure of polar bears for their conservation in a rapidly warming Arctic

We provide an expansive analysis of polar bear (Ursus maritimus) circumpolar genetic variation during the last two decades of decline in their sea-ice habitat. We sought to evaluate whether their genetic diversity and structure have changed over this period of habitat decline, how their current genetic patterns compare with past patterns, and how genetic demography changed with ancient fluctuations in climate. Characterizing their circumpolar genetic structure using microsatellite data, we defined four clusters that largely correspond to current ecological and oceanographic factors: Eastern Polar Basin, Western Polar Basin, Canadian Archipelago and Southern Canada. We document evidence for recent (ca. last 1–3 generations) directional gene flow from Southern Canada and the Eastern Polar Basin towards the Canadian Archipelago, an area hypothesized to be a future refugium for polar bears as climate-induced habitat decline continues. Our data provide empirical evidence in support of this hypothesis. The direction of current gene flow differs from earlier patterns of gene flow in the Holocene. From analyses of mitochondrial DNA, the Canadian Archipelago cluster and the Barents Sea subpopulation within the Eastern Polar Basin cluster did not show signals of population expansion, suggesting these areas may have served also as past interglacial refugia. Mismatch analyses of mitochondrial DNA data from polar and the paraphyletic brown bear (U. arctos) uncovered offset signals in timing of population expansion between the two species, that are attributed to differential demographic responses to past climate cycling. Mitogenomic structure of polar bears was shallow and developed recently, in contrast to the multiple clades of brown bears. We found no genetic signatures of recent hybridization between the species in our large, circumpolar sample, suggesting that recently observed hybrids represent localized events. Documenting changes in subpopulation connectivity will allow polar nations to proactively adjust conservation actions to continuing decline in sea-ice habitat.

Research priorities in spiritual care: an international survey of palliative care researchers and clinicians

CONTEXT

Spiritual distress, including meaninglessness and hopelessness, is common in advanced disease. Spiritual care is a core component of palliative care, yet often neglected by health care professionals owing to the dearth of robust evidence to guide practice.

OBJECTIVES

To determine research priorities of clinicians/researchers and thus inform future research in spiritual care in palliative care.

METHODS

An online, cross-sectional, mixed-methods survey was conducted. Respondents were asked whether there is a need for more research in spiritual care, and if so, to select the five most important research priorities from a list of 15 topics. Free-text questions were asked about additional research priorities and respondents' single most important research question, with data analyzed thematically.

RESULTS

In total, 971 responses, including 293 from palliative care physicians, 112 from nurses, and 111 from chaplains, were received from 87 countries. Mean age was 48.5 years (standard deviation, 10.7), 64% were women, and 65% were Christian. Fifty-three percent reported their work as "mainly clinical," and less than 2.5% stated that no further research was needed. Integrating quantitative and qualitative data demonstrated three priority areas for research: 1) development and evaluation of conversation models and overcoming barriers to spiritual care in staff attitudes, 2) screening and assessment, and 3) development and evaluation of spiritual care interventions and determining the effectiveness of spiritual care.

CONCLUSION

In this first international survey exploring researchers' and clinicians' research priorities in spiritual care, we found international support for research in this domain. Findings provide an evidence base to direct future research and highlight the particular need for methodologically rigorous evaluation studies.

Practice-centred evaluation and the privileging of care in health information technology evaluation

Our contribution, drawn from our experience of the case study provided, is a protocol for practice-centred, participative evaluation of technology in the clinical setting that privileges care. In this context 'practice-centred' evaluation acts as a scalable, coordinating framework for evaluation that recognises health information technology supported care as an achievement that is contingent and ongoing. We argue that if complex programmes of technology-enabled service innovation are understood in terms of their contribution to patient care and supported by participative, capability-building evaluation methodologies, conditions are created for practitioners and patients to realise the potential of technologies and make substantive contributions to the evidence base underpinning health innovation programmes.

BACKGROUND

Electronic Patient Records (EPRs) and telemedicine are positioned by policymakers as health information technologies that are integral to achieving improved clinical outcomes and efficiency savings. However, evaluating the extent to which these aims are met poses distinct evaluation challenges, particularly where clinical and cost outcomes form the sole focus of evaluation design. We propose that a practice-centred approach to evaluation - in which those whose day-to-day care practice is altered (or not) by the introduction of new technologies are placed at the centre of evaluation efforts - can complement and in some instances offer advantages over, outcome-centric evaluation models.

METHODS

We carried out a regional programme of innovation in renal services where a participative approach was taken to the introduction of new technologies, including: a regional EPR system and a system to support video clinics. An 'action learning' approach was taken to procurement, pre-implementation planning, implementation, ongoing development and evaluation. Participants included clinicians, technology specialists, patients and external academic researchers. Whilst undergoing these activities we asked: how can a practice-centred approach be embedded into evaluation of health information technologies?

DISCUSSION

Organising EPR and telemedicine evaluation around predetermined outcome measures alone can be impractical given the complex and contingent nature of such projects. It also limits the extent to which unforeseen outcomes and new capabilities are recognised. Such evaluations often fail to improve understanding of 'when' and 'under what conditions' technology-enabled service improvements are realised, and crucially, how such innovation improves care.

SUMMARY

Our contribution, drawn from our experience of the case study provided, is a protocol for practice-centred, participative evaluation of technology in the clinical setting that privileges care. In this context 'practice-centred' evaluation acts as a scalable, coordinating framework for evaluation that recognises health information technology supported care as an achievement that is contingent and ongoing. We argue that if complex programmes of technology-enabled service innovation are understood in terms of their contribution to patient care and supported by participative, capability-building evaluation methodologies, conditions are created for practitioners and patients to realise the potential of technologies and make substantive contributions to the evidence base underpinning health innovation programmes.

What are the toxicological effects of mercury in Arctic biota?

This review critically evaluates the available mercury (Hg) data in Arctic marine biota and the Inuit population against toxicity threshold values. In particular marine top predators exhibit concentrations of mercury in their tissues and organs that are believed to exceed thresholds for biological effects. Species whose concentrations exceed threshold values include the polar bears (Ursus maritimus), beluga whale (Delphinapterus leucas), pilot whale (Globicephala melas), hooded seal (Cystophora cristata), a few seabird species, and landlocked Arctic char (Salvelinus alpinus). Toothed whales appear to be one of the most vulnerable groups, with high concentrations of mercury recorded in brain tissue with associated signs of neurochemical effects. Evidence of increasing concentrations in mercury in some biota in Arctic Canada and Greenland is therefore a concern with respect to ecosystem health.

Effects of climate warming on polar bears: a review of the evidence

Climate warming is causing unidirectional changes to annual patterns of sea ice distribution, structure, and freeze-up. We summarize evidence that documents how loss of sea ice, the primary habitat of polar bears (Ursus maritimus), negatively affects their long-term survival. To maintain viable subpopulations, polar bears depend on sea ice as a platform from which to hunt seals for long enough each year to accumulate sufficient energy (fat) to survive periods when seals are unavailable. Less time to access to prey, because of progressively earlier breakup in spring, when newly weaned ringed seal (Pusa hispida) young are available, results in longer periods of fasting, lower body condition, decreased access to denning areas, fewer and smaller cubs, lower survival of cubs as well as bears of other age classes and, finally, subpopulation decline toward eventual extirpation. The chronology of climate-driven changes will vary between subpopulations, with quantifiable negative effects being documented first in the more southerly subpopulations, such as those in Hudson Bay or the southern Beaufort Sea. As the bears' body condition declines, more seek alternate food resources so the frequency of conflicts between bears and humans increases. In the most northerly areas, thick multiyear ice, through which little light penetrates to stimulate biological growth on the underside, will be replaced by annual ice, which facilitates greater productivity and may create habitat more favorable to polar bears over continental shelf areas in the short term. If the climate continues to warm and eliminate sea ice as predicted, polar bears will largely disappear from the southern portions of their range by mid-century. They may persist in the northern Canadian Arctic Islands and northern Greenland for the foreseeable future, but their long-term viability, with a much reduced global population size in a remnant of their former range, is uncertain.

Age and sex composition of seals killed by polar bears in the eastern Beaufort Sea

Background

Polar bears (Ursus maritimus) of the Beaufort Sea enter hyperphagia in spring and gain fat reserves to survive periods of low prey availability. We collected information on seals killed by polar bears (n = 650) and hunting attempts on ringed seal (Pusa hispida) lairs (n = 1396) observed from a helicopter during polar bear mark-recapture studies in the eastern Beaufort Sea in spring in 1985–2011. We investigated how temporal shifts in ringed seal reproduction affect kill composition and the intraspecific vulnerabilities of ringed seals to polar bear predation.

Principal Findings

Polar bears primarily preyed on ringed seals (90.2%) while bearded seals (Erignathus barbatus) only comprised 9.8% of the kills, but 33% of the biomass. Adults comprised 43.6% (150/344) of the ringed seals killed, while their pups comprised 38.4% (132/344). Juvenile ringed seals were killed at the lowest proportion, comprising 18.0% (62/344) of the ringed seal kills. The proportion of ringed seal pups was highest between 2007–2011, in association with high ringed seal productivity. Half of the adult ringed seal kills were ≥21 years (60/121), and kill rates of adults increased following the peak of parturition. Determination of sex from DNA revealed that polar bears killed adult male and adult female ringed seals equally (0.50, n = 78). The number of hunting attempts at ringed seal subnivean lair sites was positively correlated with the number of pup kills (r² = 0.30, P = 0.04), but was not correlated with the number of adult kills (P = 0.37).

Conclusions/Significance

Results are consistent with decadal trends in ringed seal productivity, with low numbers of pups killed by polar bears in spring in years of low pup productivity, and conversely when pup productivity was high. Vulnerability of adult ringed seals to predation increased in relation to reproductive activities and age, but not gender.

Differences in mercury bioaccumulation between polar bears (Ursus maritimus) from the Canadian high- and sub-Arctic

Polar bears (Ursus maritimus) are being impacted by climate change and increased exposure to pollutants throughout their northern circumpolar range. In this study, we quantified concentrations of total mercury (THg) in the hair of polar bears from Canadian high- (southern Beaufort Sea, SBS) and sub- (western Hudson Bay, WHB) Arctic populations. Concentrations of THg in polar bears from the SBS population (14.8 ± 6.6 μg g(-1)) were significantly higher than in polar bears from WHB (4.1 ± 1.0 μg g(-1)). On the basis of δ(15)N signatures in hair, in conjunction with published δ(15)N signatures in particulate organic matter and sediments, we estimated that the pelagic and benthic food webs in the SBS are ∼ 4.7 and ∼ 4.0 trophic levels long, whereas in WHB they are only ∼ 3.6 and ∼ 3.3 trophic levels long. Furthermore, the more depleted δ(13)C ratios in hair from SBS polar bears relative to those from WHB suggests that SBS polar bears feed on food webs that are relatively more pelagic (and longer), whereas polar bears from WHB feed on those that are relatively more benthic (and shorter). Food web length and structure accounted for ∼ 67% of the variation we found in THg concentrations among all polar bears across both populations. The regional difference in polar bear hair THg concentrations was also likely due to regional differences in water-column concentrations of methyl Hg (the toxic form of Hg that biomagnifies through food webs) available for bioaccumulation at the base of the food webs. For example, concentrations of methylated Hg at mid-depths in the marine water column of the northern Canadian Arctic Archipelago were 79.8 ± 37.3 pg L(-1), whereas, in HB, they averaged only 38.3 ± 16.6 pg L(-1). We conclude that a longer food web and higher pelagic concentrations of methylated Hg available to initiate bioaccumulation in the BS resulted in higher concentrations of THg in polar bears from the SBS region compared to those inhabiting the western coast of HB.

Conservation and management of Canada’s polar bears (Ursus maritimus) in a changing Arctic1This review is part of the virtual symposium “Flagship Species – Flagship Problems” that deals with ecology, biodiversity and management issues, and climate impacts on species at risk and of Canadian importance, including the polar bear (Ursus maritimus), Atlantic cod (Gadus morhua), Piping Plover (Charadrius melodus), and caribou (Rangifer tarandus)

Canada has an important responsibility for the research, conservation, and management of polar bears ( Ursus maritimus Phipps, 1774) because the majority of polar bears in the world occur within the nation’s borders. Two fundamental and recent changes for polar bears and their conservation have arisen: (1) the ongoing and projected further decline of sea-ice habitat as a result of climate change and (2) the implementation of aboriginal land claims and treaties in Canada’s North. Science has documented empirical links between productivity of polar bear population and sea-ice change. Predictive modeling based on these data has forecast significant declines in polar bear abundance and distribution of polar bears. With the signing of northern land claims and treaties, polar bear management in Canada has integrated local aboriginal participation, values, and knowledge. The interaction of scientific and local perspectives on polar bears as they relate to harvest, climate change, and declining habitat has recently caused controversy. Some conservation, management, and research decisions have been contentious because of gaps in scientific knowledge and the polarization and politicization of the roles of the various stakeholders. With these ecological and governance transitions, there is a need to re-focus and re-direct polar bear conservation in Canada.

Polar bear population status in the northern Beaufort Sea, Canada, 1971-2006

Polar bears (Ursus maritimus) of the northern Beaufort Sea (NB) population occur on the perimeter of the polar basin adjacent to the northwestern islands of the Canadian Arctic Archipelago. Sea ice converges on the islands through most of the year. We used open-population capture-recapture models to estimate population size and vital rates of polar bears between 1971 and 2006 to: (1) assess relationships between survival, sex and age, and time period; (2) evaluate the long-term importance of sea ice quality and availability in relation to climate warming; and (3) note future management and conservation concerns. The highest-ranking models suggested that survival of polar bears varied by age class and with changes in the sea ice habitat. Model-averaged estimates of survival (which include harvest mortality) for senescent adults ranged from 0.37 to 0.62, from 0.22 to 0.68 for cubs of the year (COY) and yearlings, and from 0.77 to 0.92 for 2-4 year-olds and adults. Horvtiz-Thompson (HT) estimates of population size were not significantly different among the decades of our study. The population size estimated for the 2000s was 980 +/- 155 (mean and 95% CI). These estimates apply primarily to that segment of the NB population residing west and south of Banks Island. The NB polar bear population appears to have been stable or possibly increasing slightly during the period of our study. This suggests that ice conditions have remained suitable and similar for feeding in summer and fall during most years and that the traditional and legal Inuvialuit harvest has not exceeded sustainable levels. However, the amount of ice remaining in the study area at the end of summer, and the proportion that continues to lie over the biologically productive continental shelf (< 300 m water depth) has declined over the 35-year period of this study. If the climate continues to warm as predicted, we predict that the polar bear population in the northern Beaufort Sea will eventually decline. Management and conservation practices for polar bears in relation to both aboriginal harvesting and offshore industrial activity will need to adapt.

Climate change threatens polar bear populations: a stochastic demographic analysis

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 lambda 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 lambdas, as the frequency of poor ice years increased. The observed frequency of poor ice years since 1979 would imply log lambdas approximately - 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.

The role of diet on long-term concentration and pattern trends of brominated and chlorinated contaminants in western Hudson Bay polar bears, 1991-2007

Adipose tissue was sampled from the western Hudson Bay (WHB) subpopulation of polar bears at intervals from 1991 to 2007 to examine temporal trends of PCB and OCP levels both on an individual and sum-(∑-)contaminant basis. We also determined levels and temporal trends of emerging polybrominated diphenyl ethers (PBDEs), hexabromocyclododecane (HBCD), polybrominated biphenyls (PBBs) and other current-use brominated flame retardants. Over the 17-year period, ∑DDT (and p,p'-DDE, p,p'-DDD, p,p'-DDT) decreased (-8.4%/year); α-hexachlorocyclohexane (α-HCH) decreased (-11%/year); β-HCH increased (+8.3%/year); and ∑PCB and ∑chlordane (CHL), both contaminants at highest concentrations in all years (>1ppm), showed no distinct trends even when compared to previous data for this subpopulation dating back to 1968. Some of the less persistent PCB congeners decreased significantly (-1.6%/year to -6.3%/year), whereas CB153 levels tended to increase (+3.3%/year). Parent CHLs (c-nonachlor, t-nonachlor) declined, whereas non-monotonic trends were detected for metabolites (heptachlor epoxide, oxychlordane). ∑chlorobenzene, octachlorostyrene, ∑mirex, ∑MeSO(2)-PCB and dieldrin did not significantly change. Increasing ∑PBDE levels (+13%/year) matched increases in the four consistently detected congeners, BDE47, BDE99, BDE100 and BDE153. Although no trend was observed, total-(α)-HBCD was only detected post-2000. Levels of the highest concentration brominated contaminant, BB153, showed no temporal change. As long-term ecosystem changes affecting contaminant levels may also affect contaminant patterns, we examined the influence of year (i.e., aging or "weathering" of the contaminant pattern), dietary tracers (carbon stable isotope ratios, fatty acid patterns) and biological (age/sex) group on congener/metabolite profiles. Patterns of PCBs, CHLs and PBDEs were correlated with dietary tracers and biological group, but only PCB and CHL patterns were correlated with year. DDT patterns were not associated with any explanatory variables, possibly related to local DDT sources. Contaminant pattern trends may be useful in distinguishing the possible role of ecological/diet changes on contaminant burdens from expected dynamics due to atmospheric sources and weathering.

Ecological dynamics across the Arctic associated with recent climate change

At the close of the Fourth International Polar Year, we take stock of the ecological consequences of recent climate change in the Arctic, focusing on effects at population, community, and ecosystem scales. Despite the buffering effect of landscape heterogeneity, Arctic ecosystems and the trophic relationships that structure them have been severely perturbed. These rapid changes may be a bellwether of changes to come at lower latitudes and have the potential to affect ecosystem services related to natural resources, food production, climate regulation, and cultural integrity. We highlight areas of ecological research that deserve priority as the Arctic continues to warm.

Isotopic homogeneity of breath CO2 from fasting and berry-eating polar bears: implications for tracing reliance on terrestrial foods in a changing Arctic

With a changing Arctic climate, it is important to know whether polar bears ( Ursus maritimus Phipps, 1774) can supplement their stored fat reserves by intake of terrestrial berries. Although polar bears are known to consume berries while on land, it has been difficult to quantify their relative dependence on stored adipose tissue and berry carbohydrates to meet their energy needs. We sampled breath CO2 from 300 bears fasting on land in western Hudson Bay during the open-water seasons of 1997 and 1998 and analyzed this breath for stable carbon isotope (δ13C) values. We found no difference in the bear breath δ13C values for bears known to have recently fed on berries and those that had not. The distribution of δ13C values was remarkably tight with average values ranging from –24.2‰ to –24.8‰ with no effect of age, sex, or year of capture. This result was counter to our simple isotopic discrimination model that predicted bears metabolizing adipose tissue derived from seals would have breath δ13C values close to –24.7‰ and those metabolizing berries exclusively would have values close to –32.6‰. If correct, our results suggests that the bears which had fed on berries while fasting on land received an insignificant amount of energetic benefit.