小兴安岭林区黑熊对冬眠仓的选择

2002年11月至2003年4月、2003年11月至2004年3月,在东北小兴安岭林区对黑熊冬眠仓的特征和仓址选择进行了研究.采用网状排查的方法,调查熊仓111个和未被利用的树洞(26)、岩洞(12),其中树仓72个,地仓36个,明仓3个.结果表明:72个利用树仓和26个未利用树洞的坡度和灌丛盖度差异显著;坡度、灌丛盖度、仓口到地面高度、海拔、树高等因子与利用状况关联紧密;黑熊对树仓周围植被偏好利用针叶林和杂木林,回避阔叶林,对针阔叶混交林生境随机利用;对树仓的洞口有选择性,选择利用只有一个上洞口或侧口的树洞,回避有多个洞口的树洞;而对坡向、坡位、树种、枯树/活树和洞口朝向的利用无选择性.36个利用地仓和12个未利用岩洞的树高和坡度差异极显著,人为干扰距离因子差异显著,其余各项数量型因子差异不显著;树高、坡度、人为干扰距离、灌丛盖度、仓口长和海拔等因子与利用状况关联紧密.黑熊对地仓偏好利用上坡位和中坡位,回避下坡位;对地仓的洞口朝向选择利用仓口朝向阳面的地仓,回避阴面,对洞口朝向半阴半阳面的地仓随机利用.对植被类型、坡向、树种、枯树/活树和树洞/岩洞的利用无选择性.在小兴安岭南坡的带岭林区研究中还发现,当树仓、地仓被火烧过以后,将不再被黑熊利用;但是黑熊并不离开冬眠巢域,而是就地自建巢穴,利用明仓过冬.     

Variation in life history and demography of the American black bear

Variation in life history and demography across a species' range informs researchers about regional adaptations and affects whether managers can borrow information from other populations in decision-making. The American black bear (Ursus americanus) is a long-lived game species whose continued persistence depends on management of harvest and removal of habituated bears that come into conflict with humans. Understanding the demography of black bears guides efforts at management and conservation, yet detailed knowledge of many populations is typically lacking. I performed a hierarchical Bayesian meta-analysis of black bear demographic studies across the geographic range of the species to explore how vital rates vary across the range, what information they give us about population growth, and whether managers can justify borrowing information from other studies to inform management decisions. Cub, yearling, and adult survival and fecundity varied between eastern and western North America, whereas subadult survival did not show geographic structuring. Adult survival and fecundity appeared to trade off, with higher survival in the western portions of bears' range and higher fecundity in the east. Although adult survival had the highest elasticity, differences in reproduction drove differences in population growth rate. Mean population growth rate was higher in the east (0.99; 95% credible interval [CrI]: 0.96, 1.03) than the west (0.97; 95%CrI: 0.93, 1.01). Despite declining trends in the west, 34% of the distribution of population growth rate was >1, compared to 55% in the east. Further work needs to be done to address the cause of the apparent trade-off between adult survival and fecundity and explore how the estimated growth rates are likely to affect population status of black bears. Because population growth rates are close to 1 and small deviations could impact whether a population is considered increasing or decreasing, managers need to employ caution in borrowing vital rates from other populations. © 2011 The Wildlife Society.     

Fatal attacks by American black bear on people: 1900–2009

At least 63 people were killed in 59 incidents by non-captive black bear (Ursus americanus) during 1900–2009. Fatal black bear attacks occurred in Canada and Alaska (n = 49) and in the lower 48 states (n = 14). There were 3.5 times as many fatal attacks in Canada and Alaska but only 1.75 times as many black bears, and much less human contact for black bears in Canada and Alaska. There was a weak positive correlation (r_s = 0.56, P ≤ 0.000) between the estimated size of a bear population within a given jurisdiction and the number of fatal black bear attacks. Some jurisdictions had no fatal black bear attacks but had large estimated black bear populations. Of fatal attacks, 86% (54 of 63, 1.08/yr) occurred between 1960 and 2009. There was positive linear relationship between the number of fatal black bear attacks per decade and human population size in the United States and Canada per decade (r² = 0.92, β = 0.000, P ≤ 0.001). Of fatal attacks, 91% (49 of 54) occurred on parties of 1 or 2 persons. In 38% (15 of 40) of incidents, peoples' food or garbage probably influenced the bear being in the attack location. We judged that the bear involved acted as a predator in 88% (49 of 56) of fatal incidents. Adult (n = 23) or subadult (n = 10) male bears were involved in 92% (33 of 36) of fatal predatory incidents, reflecting biological and behavioral differences between male and female bears. That most fatal black bear attacks were predatory and were carried out by 1 bear shows that females with young are not the most dangerous black bears. As a result of our research agencies managing black bear can more accurately understand the risk of being killed by a black bear, and can communicate this to the public. With training, people can learn to recognize the behaviors of a bear considering them as prey and can act to deter predation. © 2011 The Wildlife Society.     

Demography and population viability of polar bears in the Gulf of Boothia, Nunavut

We estimated demographic parameters and harvest risks for polar bears ( Ursus maritimus ) inhabiting the Gulf of Boothia, Nunavut, from 1976 to 2000. We computed survival and abundance from capture–recapture and recovery data (630 marks) using a Burnham joint live–dead model implemented in program MARK. Annual mean total survival (including harvest) was 0.889 ± 0.179 (± 1 SE) for cubs, 0.883 ± 0.087 for subadults (ages 1–4), 0.919 ± 0.044 for adult females, and 0.917 ± 0.041 for adult males. Abundance in the last 3 yr of study was 1,592 ± 361 bears. Mean size of newborn litters was 1.648 ± 0.098 cubs. By age 7, 0.97 ± 0.30 of available females were producing litters. Harvest averaged 38.4 ± 4.2 bears/year in the last 5 yr of study; however, the 2002–2007 kill averaged 56.4 bears/yr. We used a harvested Population Viability Analysis (PVA) to examine impacts of increasing rates of harvest. We estimated the current population growth rate, λ _H , to be 1.025 ± 0.032. Although this suggests the population is growing, progressive environmental changes may require more frequent population inventory studies to maintain the same levels of harvest risk.     

Genetic diversity of endangered brown bear (Ursus arctos) populations at the crossroads of Europe, Asia and Africa

Aim  Middle East brown bears ( Ursus arctos syriacus Hemprich and Ehrenberg, 1828) are presently on the edge of extinction. However, little is known of their genetic diversity. This study investigates that question as well as that of Middle East brown bear relationships to surrounding populations of the species.
Location  Middle East region of south-western Asia.
Methods  We performed DNA analyses on 27 brown bear individuals. Twenty ancient bone samples (Late Pleistocene to 20th century) from natural populations and seven present-day samples obtained from captive individuals were analysed.
Results  Phylogenetic analyses of the mitochondrial sequences obtained from seven ancient specimens identify three distinct maternal clades, all unrelated to one recently described from North Africa. Brown bears from Iran exhibit striking diversity (three individuals, three haplotypes) and form a unique clade that cannot be linked to any extant one. Individuals from Syria belong to the Holarctic clade now observed in Eastern Europe, Turkey, Japan and North America. Specimens from Lebanon surprisingly appear as tightly linked to the clade of brown bears now in Western Europe. Moreover, we show that U. a. syriacus in captivity still harbour haplotypes closely linked to those found in ancient individuals.
Main conclusion  This study brings important new information on the genetic diversity of brown bear populations at the crossroads of Europe, Asia and Africa. It reveals a high level of diversity in Middle East brown bears and extends the historical distribution of the Western European clade to the East. Our analyses also suggest the value of a specific breeding programme for captive populations.     

DOES VARIATION IN SELECTION IMPOSED BY BEARS DRIVE DIVERGENCE AMONG POPULATIONS IN THE SIZE AND SHAPE OF SOCKEYE SALMON?

Few studies have determined whether formal estimates of selection explain patterns of trait divergence among populations, yet this is one approach for evaluating whether the populations are in equilibria. If adaptive divergence is complete, directional selection should be absent and stabilizing selection should prevail. We estimated natural selection, due to bear predation, acting on the body size and shape of male salmon in three breeding populations that experience differing predation regimes. Our approach was to (1) estimate selection acting within each population on each trait based on an empirical estimate of reproductive activity, (2) test for trait divergence among populations, and (3) test whether selection coefficients were correlated with trait divergence among populations. Stabilizing selection was never significant, indicating that these populations have yet to attain equilibria. Directional selection varied among populations in a manner consistent with trait divergence, indicating ongoing population differentiation. Specifically, the rank order of the creeks in terms of patterns of selection paralleled the rank order in terms of size and shape. The shortest and least deep-bodied males had the highest reproductive activity in the creek with the most intense predation and longer and deeper-bodied males were favored in the creeks with lower predation risk.     

Litter loss triggers estrus in a nonsocial seasonal breeder

Sexually selected infanticide (SSI) is often presumed to be rare among seasonal breeders, because it would require a near immediate return to estrus after the loss of an entire litter during the mating season. We evaluated changes in reproductive strategies and the reproductive fate of females that experienced litter loss during the mating season in a seasonal breeder with strong evidence for SSI, the brown bear. First, we used a long‐term demographic dataset (1986–2011) to document that a large majority of females (>91%) that lose their entire litter during the mating season in fact do enter estrus, mate, and give birth during the subsequent birthing season. Second, we used high‐resolution movement data (2005–2011) to evaluate how females changed reproductive strategies after losing their entire litter during the mating season. We hypothesized that females would shift from the sedentary lifestyle typical for females with cubs‐of‐the‐year to a roam‐to‐mate behavior typical for receptive females in no more than a few (~3) days after litter loss. We found that females with cubs‐of‐the‐year moved at about 1/3 of the rate and in a less bimodal diurnal pattern than receptive females during the mating season. The probability of litter loss was positively related with movement rate, suggesting that being elusive and sedentary is a strategy to enhance cub survival rather than a relic of cub mobility itself. The movement patterns of receptive females and females after litter loss were indistinguishable within 1–2 days after the litter loss, and we illustrate that SSI can significantly reduce the female interbirth interval (50–85%). Our results suggest that SSI can also be advantageous for males in seasonally breeding mammals. We propose that infanticide as a male reproductive strategy is more prevalent among mammals with reproductive seasonality than observed or reported.     

Differential habitat use between demographic states of black bears in managed timber forests

The long-term effects of intensive forest harvest on sensitive demographic stages of the American black bear (Ursus americanus) have been often overlooked. Much of Maine, USA, is covered in forests that are hospitable to bears and commercial timber harvest. To investigate the potential effects of differing intensities of disturbance on black bears, and on females with cubs particularly, we designed a large-scale natural experiment with 197 motion-sensitive camera sites dispersed over representative forest stands in northern and central Maine. Using multi-state occupancy models, we distinguished the overall trends in space use by females with young versus adult bears without young. Forest disturbance at large spatial scales was positively associated with the probability of use for both demographic groups and the availability of hardwood trees was an additional important factor for habitat use by females with young. Our study illustrates the use of motion-sensitive cameras to monitor and understand habitat use by distinct life-history stages of animals living in human-modified landscapes, and results indicate that managers can maintain black bear habitat in areas of active forest harvest by ensuring the availability of hardwood species.