Martyn E. Obbard

Polar and brown bear genomes reveal ancient admixture and demographic footprints of past climate change

Polar bears (PBs) are superbly adapted to the extreme Arctic environment and have become emblematic of the threat to biodiversity from global climate change. Their divergence from the lower-latitude brown bear provides a textbook example of rapid evolution of distinct phenotypes. However, limited mitochondrial and nuclear DNA evidence conflicts in the timing of PB origin as well as placement of the species within versus sister to the brown bear lineage. We gathered extensive genomic sequence data from contemporary polar, brown, and American black bear samples, in addition to a 130,000- to 110,000-y old PB, to examine this problem from a genome-wide perspective. Nuclear DNA markers reflect a species tree consistent with expectation, showing polar and brown bears to be sister species. However, for the enigmatic brown bears native to Alaskas Alexander Archipelago, we estimate that not only their mitochondrial genome, but also 5–10% of their nuclear genome, is most closely related to PBs, indicating ancient admixture between the two species. Explicit admixture analyses are consistent with ancient splits among PBs, brown bears and black bears that were later followed by occasional admixture. We also provide paleodemographic estimates that suggest bear evolution has tracked key climate events, and that PB in particular experienced a prolonged and dramatic decline in its effective population size during the last ca. 500,000 years. We demonstrate that brown bears and PBs have had sufficiently independent evolutionary histories over the last 4–5 million years to leave imprints in the PB nuclear genome that likely are associated with ecological adaptation to the Arctic environment.

Correlations of plasma lipid metabolites with hibernation and lactation in wild black bears Ursus americanus

Abstract. During the denning period, black bears (Ursus americanus) are capable of enduring several months without food. At the same time, female bears that are pregnant or lactating have an added metabolic stress. Based on laboratory studies, much of the energy required to support metabolism and lactation during denning in black bears comes from lipid reserves. These lipid reserves are mobilized and the most metabolically active lipid fraction in the blood are nonesterified fatty acids (NEFA). Therefore, we hypothesized that plasma NEFAs would be higher in denning relative to active bears and in lactating relative to non-lactating female bears. We further hypothesized that in bears with elevated plasma NEFA levels, other lipid-related parameters (e.g., ketone bodies, albumin, cholesterol, lipase) would also be elevated in the plasma. Denning bears had significantly increased NEFA levels in all classes (saturates, monoenes, and polyenes). A doubling of plasma NEFA levels and a 33% increase in albumin, the plasma fatty acid binding protein, in denning bears, resulted in NEFA/albumin ratios that were higher in denning bears (4:1) compared to those of active bears (3:1). Bears became relatively ketonemic with a 17-fold increase in D-β-hydroxybutyrate levels during the denning period. Plasma cholesterol approximately doubled and lipase was ten-fold lower in denning relative to active bears. These findings indicate a strong correlation between plasma lipid metabolites and the denning period in a wild population of black bears.

A circumpolar monitoring framework for polar bears

Abstract Polar bears (Ursus maritimus) occupy remote regions that are characterized by harsh weather and limited access. Polar bear populations can only persist where temporal and spatial availability of sea ice provides adequate access to their marine mammal prey. Observed declines in sea ice availability will continue as long as greenhouse gas concentrations rise. At the same time, human intrusion and pollution levels in the Arctic are expected to increase. A circumpolar understanding of the cumulative impacts of current and future stressors is lacking, long-term trends are known from only a few subpopulations, and there is no globally coordinated effort to monitor effects of stressors. Here, we describe a framework for an integrated circumpolar monitoring plan to detect ongoing patterns, predict future trends, and identify the most vulnerable polar bear subpopulations. We recommend strategies for monitoring subpopulation abundance and trends, reproduction, survival, ecosystem change, human-caused mortality, human–bear conflict, prey availability, health, stature, distribution, behavioral change, and the effects that monitoring itself may have on polar bears. We assign monitoring intensity for each subpopulation through adaptive assessment of the quality of existing baseline data and research accessibility. A global perspective is achieved by recommending high intensity monitoring for at least one subpopulation in each of four major polar bear ecoregions. Collection of data on harvest, where it occurs, and remote sensing of habitat, should occur with the same intensity for all subpopulations. We outline how local traditional knowledge may most effectively be combined with the best scientific methods to provide comparable and complementary lines of evidence. We also outline how previously collected intensive monitoring data may be sub-sampled to guide future sampling frequencies and develop indirect estimates or indices of subpopulation status. Adoption of this framework will inform management and policy responses to changing worldwide polar bear status and trends.

A body composition model to estimate mammalian energy stores and metabolic rates from body mass and body length, with application to polar bears

SUMMARY Many species experience large fluctuations in food availability and depend on energy from fat and protein stores for survival, reproduction and growth. Body condition and, more specifically, energy stores thus constitute key variables in the life history of many species. Several indices exist to quantify body condition but none can provide the amount of stored energy. To estimate energy stores in mammals, we propose a body composition model that differentiates between structure and storage of an animal. We develop and parameterize the model specifically for polar bears (Ursus maritimus Phipps) but all concepts are general and the model could be easily adapted to other mammals. The model provides predictive equations to estimate structural mass, storage mass and storage energy from an appropriately chosen measure of body length and total body mass. The model also provides a means to estimate basal metabolic rates from body length and consecutive measurements of total body mass. Model estimates of body composition, structural mass, storage mass and energy density of 970 polar bears from Hudson Bay were consistent with the life history and physiology of polar bears. Metabolic rate estimates of fasting adult males derived from the body composition model corresponded closely to theoretically expected and experimentally measured metabolic rates. Our method is simple, non-invasive and provides considerably more information on the energetic status of individuals than currently available methods.

Demography of Black Bears in Hunted and Unhunted Areas of the Boreal Forest of Ontario

Abstract We estimated relative density, survival, and reproduction of American black bears (Ursus americanus) from capture–recapture and telemetry data collected from 1989 to 1999 in the unhunted Chapleau Crown Game Preserve (CCGP) and nearby hunted areas in the boreal forest of Ontario, Canada. We tested for combinations of effects of age class, sex, year, years of food shortage, encumbrance status, and residency (on or off the Game Preserve) on vital rates. Results from live captures, remote captures, and bait-station hit rates indicated that density was highest inside CCGP. Total survival of adult females, subadults, and cubs were similar among residents and nonresidents of CCGP, but yearling survival was lower among CCGP residents. Adult females were approximately twice as likely to die and nearly 10 times as likely to be cannibalized (risk ratio [RR] = 9.62, 95% CI = 2.088–44.29) while encumbered with cubs of the year. Nonresidents of CCGP had greater risk of being harvested (RR = 4.00, 95% CI = 1.19–13.46) but similar risk of being cannibalized (RR = 0.875, 95% CI = 0.300–2.55) relative to CCGP residents, suggesting that harvest mortality was additive to other forms of mortality. Residents of CCGP had older ages at primiparity and lower litter-production rates than bears resident in hunted areas. Few litters were produced in years following food shortages, but litter size was unaffected. We recommend that managers allow for additive harvest mortality and reduced survival of bears encumbered with cubs of the year, and we caution that assuming density-compensatory increases in cub production could optimistically bias estimates of population growth.

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.

Do public complaints reflect trends in human–bear conflict?

Abstract Minimizing conflicts with humans is a necessary component of the management of American black bears (Ursus americanus) across most of their range. The number of complaints about conflicts with black bears is commonly used to infer trends in the actual frequency or severity of human–bear conflict, and even trends in bear population size. However, the number of complaints received by management agencies is a function of both the frequency of and the reporting rate for conflicts, and the reporting rate may change over time. We tested for effects of food availability, numbers of bears harvested, and management regime changes on 3 measures of human–bear conflict: (1) public complaints, (2) traps set to capture bears involved in conflicts, and (3) bears killed in defense of property in Parry Sound, Ontario, Canada, 1992–2008. All measures of human–bear conflict were inversely related to food availability. Complaints increased following a controversial change in management (cancellation of the spring hunting season), but numbers of traps set and bears killed were not affected. We suggest that an increase in the reporting rate was largely responsible for the increase in complaints following the spring hunt cancellation because (1) an effect on the actual frequency or severity of human–bear conflict should also have been detected in data for traps set but was not, and (2) neither the number nor the sex ratio of harvested bears changed when the spring hunt was cancelled, so the effect of harvest on population size and sex ratio was not altered by the management regime change. Trends in the actual frequency and severity of human–bear conflict should not be inferred from trends in complaint data unless factors that could affect the reporting rate for conflicts are accounted for.

Polar Bear Ecology and Management in Hudson Bay in the Face of Climate Change

Hudson Bay, Canada has been a region of intensive research on polar bear population ecology dating back to the late 1960s. Although the impacts of climate change on sea ice habitat throughout the circumpolar range of the species is of concern, Hudson Bay is the only region where the duration of sea ice cover has been linked empirically with declines in a suite of parameters: polar bear body condition; individual survival; natality; and population size. Research in Hudson Bay has also focused on contaminants in polar bear tissues, population genetics, behaviour and denning, as well as predator-prey interactions. These decades of research in Hudson Bay provide important baseline information with which to monitor the rate and extent of the impact of climate change on polar bear ecology. Climate change has already become a critical issue for polar bear management in the region; human–bear conflicts in Nunavut have increased, which had been an explicit prediction of an effect of climate change. In addition, relative to polar bear numbers in the early 1960s – before government-based harvest management – polar bear abundance has also increased. The recent empirical data demonstrating a decline in the Western Hudson Bay polar bear subpopulation has been interpreted as incongruous with observations of respected Inuit elders of the marked increase in polar bears from historical numbers, catalyzing divergent views on polar bear management. Lastly, should the duration of the ice-free season continue to increase, industrial shipping and future mining and oil and gas developments will affect polar bears in the region in ways that are not well understood. We review current knowledge of polar bear ecology in Hudson Bay, as it relates to climate change, and present an overview of future research needs and management challenges.

Conservation status of polar bears (Ursus maritimus) in relation to projected sea-ice declines.

Loss of Arctic sea ice owing to climate change is the primary threat to polar bears throughout their range. We evaluated the potential response of polar bears to sea-ice declines by (i) calculating generation length (GL) for the species, which determines the timeframe for conservation assessments; (ii) developing a standardized sea-ice metric representing important habitat; and (iii) using statistical models and computer simulation to project changes in the global population under three approaches relating polar bear abundance to sea ice. Mean GL was 11.5 years. Ice-covered days declined in all subpopulation areas during 1979–2014 (median −1.26 days year−1). The estimated probabilities that reductions in the mean global population size of polar bears will be greater than 30%, 50% and 80% over three generations (35–41 years) were 0.71 (range 0.20–0.95), 0.07 (range 0–0.35) and less than 0.01 (range 0–0.02), respectively. According to IUCN Red List reduction thresholds, which provide a common measure of extinction risk across taxa, these results are consistent with listing the species as vulnerable. Our findings support the potential for large declines in polar bear numbers owing to sea-ice loss, and highlight near-term uncertainty in statistical projections as well as the sensitivity of projections to different plausible assumptions.

Relationships among food availability, harvest, and human–bear conflict at landscape scales in Ontario, Canada

Abstract Managers of American black bears (Ursus americanus) must maintain populations to ensure viability and opportunities for sport harvest, and minimize human–bear conflict (HBC). Harvest is a cost-effective management tool in most jurisdictions, and intuitively it seems that with fewer bears, there should be fewer conflicts. Therefore, managers may attempt to achieve both objectives by manipulating the harvest. Further, because data describing harvest and HBC are frequently collected, managers sometimes infer changes in population status from trends in harvest and HBC. However, evidence that larger harvests reduce HBC is lacking, and changes in harvest metrics and the frequency of HBC may be independent of bear density. Understanding relationships among food availability, hunter effort, harvest, and HBC could help managers avoid making invalid inferences about population status from data describing harvest and HBC, and evaluate whether management actions are having intended results. We investigated relationships among food availability, HBC, and harvest at landscape scales in Ontario, Canada, 2004–2011. We hypothesized that HBC and harvest would be negatively correlated with food availability; that HBC would be negatively correlated with prior harvest; and that harvest would be positively correlated with number of hunters. We used Spearman rank correlation to test hypotheses. Human–bear conflict was negatively correlated with food availability across Ontario, and in the 2 administrative regions where food availability varied synchronously. Total harvest and the proportion of females in the harvest were negatively correlated with food availability across Ontario and in one region. Human–bear conflict was not correlated with prior harvests, providing no evidence that larger harvests reduced subsequent HBC. Given the variation in natural foods, harvest is unlikely to prevent elevated levels of HBC in years of food shortage unless it maintains bears at low densities—an objective that might conflict with maintaining viable populations and providing opportunities for sport harvest.