School of Biological Sciences, Monash University, 25 Rainforest Walk, Clayton, 3800, Victoria, Australia.
Faculty of Veterinary Medicine, University of Zagreb, Heinzelova 55, Zagreb, 10000, Croatia.
Biol Rev Camb Philos Soc. 2023 Feb;98(1):168-190. doi: 10.1111/brv.12902. Epub 2022 Sep 29.
Stress responses, which are mediated by the neurogenic system (NS) and hypothalamic-pituitary-adrenal (HPA) axis help vertebrates maintain physiological homeostasis. Fight-or-flight responses are activated by the NS, which releases norepinephrine/noradrenaline and epinephrine/adrenaline in response to immediate stressors, whilst the HPA axis releases glucocorticoid hormones (e.g. cortisol and corticosterone) to help mitigate allostatic load. There have been many studies on stress responses of captive animals, but they are not truly reflective of typical ranges or the types of stressors encountered by free-ranging wildlife, such as responses and adaptation to environmental change, which are particularly important from a conservation perspective. As stress can influence the composition of age and sex classes of free-ranging populations both directly and indirectly, ecological research must be prioritised towards more vulnerable taxa. Generally, large predators tend to be particularly at risk of anthropogenically driven population declines because they exhibit reduced behavioural plasticity required to adapt to changing landscapes and exist in reduced geographic ranges, have small population sizes, low fecundity rates, large spatial requirements and occupy high trophic positions. As a keystone species with a long history of coexistence with humans in highly anthropogenic landscapes, there has been growing concern about how humans influence bear behaviour and physiology, via numerous short- and long-term stressors. In this review, we synthesise research on the stress response in free-ranging bear populations and evaluate the effectiveness and limitations of current methodology in measuring stress in bears to identify the most effective metrics for future research. Particularly, we integrate research that utilised haematological variables, cardiac monitors and Global Positioning System (GPS) collars, serum/plasma and faecal glucocorticoid concentrations, hair cortisol levels, and morphological metrics (primarily skulls) to investigate the stress response in ursids in both short- and long-term contexts. We found that in free-ranging bears, food availability and consumption have the greatest influence on individual stress, with mixed responses to anthropogenic influences. Effects of sex and age on stress are also mixed, likely attributable to inconsistent methods. We recommend that methodology across all stress indicators used in free-ranging bears should be standardised to improve interpretation of results and that a wider range of species should be incorporated in future studies.
应激反应是由神经系统（NS）和下丘脑-垂体-肾上腺（HPA）轴介导的，有助于脊椎动物维持生理稳态。战斗或逃跑反应由 NS 激活，NS 会在遇到即时应激源时释放去甲肾上腺素/肾上腺素和肾上腺素/去甲肾上腺素，而 HPA 轴则释放糖皮质激素（如皮质醇和皮质酮）来帮助减轻适应不良的负荷。已经有许多关于圈养动物应激反应的研究，但这些研究并不能真正反映野生动物的典型范围或遇到的应激源类型，例如对环境变化的反应和适应，从保护的角度来看，这一点尤其重要。由于应激可以直接和间接地影响自由放养种群的年龄和性别结构，因此生态研究必须优先考虑更脆弱的分类群。一般来说，大型捕食者由于表现出适应不断变化的景观所需的行为可塑性降低，并且存在地理范围缩小、种群规模小、繁殖率低、空间需求大以及处于高营养级等情况，因此特别容易受到人为驱动的种群减少的影响。作为一种与人类在高度人为化景观中共同生存了很长时间的关键物种，人们越来越关注人类通过各种短期和长期应激源如何影响熊的行为和生理。在本综述中，我们综合了有关自由放养熊种群应激反应的研究，并评估了当前测量熊应激的方法的有效性和局限性，以确定未来研究最有效的指标。特别是，我们整合了利用血液学变量、心脏监测器和全球定位系统（GPS）项圈、血清/血浆和粪便皮质醇浓度、毛发皮质醇水平以及形态学指标（主要是头骨）来研究短期和长期环境中熊应激反应的研究。我们发现，在自由放养的熊中，食物的可获得性和消耗对个体应激的影响最大，而对人为影响的反应则各不相同。性别和年龄对压力的影响也各不相同，这可能归因于方法不一致。我们建议，应标准化所有用于自由放养熊的应激指标的方法，以提高对结果的解释，并在未来的研究中纳入更多的物种。
