Wildlife Biology Program, Department of Ecosystem and Conservation Sciences, University of Montana, Missoula, MT 59812, USA.
J Anim Ecol. 2011 Nov;80(6):1246-57. doi: 10.1111/j.1365-2656.2011.01856.x. Epub 2011 May 25.
1. Understanding the interaction among predators and between predation and climate is critical to understanding the mechanisms for compensatory mortality. We used data from 1999 radio-marked neonatal elk (Cervus elaphus) calves from 12 populations in the north-western United States to test for effects of predation on neonatal survival, and whether predation interacted with climate to render mortality compensatory. 2. Weibull survival models with a random effect for each population were fit as a function of the number of predator species in a community (3-5), seven indices of climatic variability, sex, birth date, birth weight, and all interactions between climate and predators. Cumulative incidence functions (CIF) were used to test whether the effects of individual species of predators were additive or compensatory. 3. Neonatal elk survival to 3 months declined following hotter previous summers and increased with higher May precipitation, especially in areas with wolves and/or grizzly bears. Mortality hazards were significantly lower in systems with only coyotes (Canis latrans), cougars (Puma concolor) and black bears (Ursus americanus) compared to higher mortality hazards experienced with gray wolves (Canis lupus) and grizzly bears (Ursus horribilis). 4. In systems with wolves and grizzly bears, mortality by cougars decreased, and predation by bears was the dominant cause of neonatal mortality. Only bear predation appeared additive and occurred earlier than other predators, which may render later mortality by other predators compensatory as calves age. Wolf predation was low and most likely a compensatory source of mortality for neonatal elk calves. 5. Functional redundancy and interspecific competition among predators may combine with the effects of climate on vulnerability to predation to drive compensatory mortality of neonatal elk calves. The exception was the evidence for additive bear predation. These results suggest that effects of predation by recovering wolves on neonatal elk survival, a contentious issue for management of elk populations, may be less important than the composition of the predator community. Future studies would benefit by synthesizing overwinter calf and adult-survival data sets, ideally from experimental studies, to test the roles of predation in annual compensatory and additive mortality of elk.
了解捕食者之间的相互作用以及捕食作用与气候之间的关系，对于理解补偿性死亡的机制至关重要。我们使用了来自美国西北部 12 个种群的 1999 年被无线电标记的新生麋鹿（Cervus elaphus）幼崽的数据，以检验捕食对新生幼崽存活率的影响，以及捕食作用是否与气候相互作用导致死亡率具有补偿性。
我们根据群落中捕食者物种的数量（3-5 种）、7 种气候变异性指标、性别、出生日期、出生体重以及气候与捕食者之间的所有相互作用，为每个种群拟合了具有随机效应的威布尔生存模型。使用累积发病率函数（CIF）来检验个别捕食物种的影响是相加的还是补偿性的。
新生麋鹿在较热的前一个夏季后到 3 个月大时的存活率下降，而在 5 月份降水较高时的存活率上升，尤其是在有狼和/或灰熊的地区。与灰狼（Canis lupus）和灰熊（Ursus horribilis）较高的死亡率相比，只有郊狼（Canis latrans）、美洲狮（Puma concolor）和黑熊（Ursus americanus）的系统中的死亡率风险显著较低。
在有狼和灰熊的系统中，美洲狮的捕食死亡率下降，而熊的捕食则是新生幼崽死亡的主要原因。只有熊的捕食似乎是相加的，而且比其他捕食者更早发生，这可能会使随着幼崽年龄的增长，其他捕食者的后期死亡率具有补偿性。狼的捕食率较低，而且很可能是新生麋鹿幼崽补偿性死亡的来源。
捕食者之间的功能冗余和种间竞争，再加上气候对捕食脆弱性的影响，可能会导致新生麋鹿幼崽的补偿性死亡。唯一的例外是熊捕食的证据表明是相加的。这些结果表明，恢复中的狼对新生麋鹿生存的影响（这是管理麋鹿种群的一个有争议的问题）可能不如捕食者群落的组成重要。未来的研究将从综合冬季幼崽和成年生存数据集中受益，理想情况下是从实验研究中，以检验捕食作用在麋鹿年度补偿性和相加性死亡率中的作用。
