Natural controls on the distribution, abundance, or growth rates of exotic species are a desirable mode of intervention because of lower costs compared to anthropogenic controls and greater social acceptance. In the Great Basin, cougars (Puma concolor) are the most widely distributed carnivore capable of killing large ungulate prey. Populations of feral horses (Equus ferus) are widely distributed throughout the Great Basin and can grow at rates up to 20%/year. Although cougars exhibit distributional overlap with horses, it has been assumed that predation is minimal because of differences in habitat use and body-size limitations. To evaluate this hypothesis, we monitored the diets of 21 global positioning system (GPS)-collared cougars in the western Great Basin (5 males, 8 females) and eastern Sierra Nevada (2 males, 6 females) from 2009–2012. We investigated 1,310 potential kill sites and located prey remains of 820 predation events. We compared prey composition and kill rates of cougars inhabiting the Sierra Nevada and Great Basin, and among male and female cougars across seasons. We used generalized linear mixed models (GLMMs) to examine the effects of prey availability and habitat characteristics on the probability of predation on horses by cougars. Mule deer (Odocoileus hemionus) comprised 91% of prey items killed on the Sierra Nevada reference site but only comprised 29% of prey items in the Great Basin study area. Average annual kill rates for deer differed between the Sierra Nevada ( = 0.85 deer/week, range = 0.44–1.3) and Great Basin ( = 0.21 deer/week, range = 0.00–0.43). Diets of cougars in the Great Basin were composed predominantly of horses (59.6%, n = 460 prey items; 13 individuals). Ten cougars regularly consumed horses, and horses were the most abundant prey in the diet of 8 additional individuals in the Great Basin. Cougars on average killed 0.38 horses/week in the Great Basin (range=0.00–0.94 horses/week). Differences in predation on horses between the sexes of cougars were striking; Great Basin females incorporated more horses across all age classes year-round, whereas male cougars tended to exploit neonatal young during spring and summer before switching to deer during winter. Within GLMM models, the probability of predation on horses compared to other prey species increased with elevation, horse density, and decreasing density of mule deer on the landscape, and was more likely to occur in sagebrush (Artemesia spp.) than in pinyon (Pinus monophylla)–juniper (Juniperus osteosperma) forests. Behavior of individual cougars accounted for more than a third of the variation explained by our top models predicting predation on horses in the Great Basin. At landscape scales, cougar predation is unlikely to limit the growth of feral horse populations. In the Great Basin ecosystem, however, cougars of both sexes successfully preyed on horses of all age classes. Moreover, some reproductive, female cougars were almost entirely dependent on feral horses year-round. Taken together, our data suggest that cougars may be an effective predator of feral horses, and that some of our previous assumptions about this relationship should be reevaluated and integrated into management and planning. © 2021 The Wildlife Society.

中文翻译：

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美洲狮在沙漠环境中对野马的猎物专业化

对外来物种的分布、丰度或增长率进行自然控制是一种理想的干预模式，因为与人为控制相比成本更低，社会接受度更高。在大盆地，美洲狮（美洲狮）是分布最广的食肉动物，能够杀死大型有蹄类动物。野马种群（Equus ferus) 广泛分布在整个大盆地，并且可以以高达 20%/年的速度增长。尽管美洲狮在分布上与马有重叠，但由于栖息地使用和体型限制的差异，人们认为捕食是最小的。为了评估这一假设，我们在 2009 年至 2012 年间监测了大盆地西部（5 只雄性，8 只雌性）和内华达山脉东部（2 只雄性，6 只雌性）的 21 只戴全球定位系统 (GPS) 项圈的美洲狮的饮食。我们调查了 1,310 个潜在的杀戮地点，并找到了 820 次捕食事件的猎物遗骸。我们比较了栖息在内华达山脉和大盆地的美洲狮，以及不同季节的雄性和雌性美洲狮的猎物成分和死亡率。我们使用广义线性混合模型 (GLMM) 来检查猎物可用性和栖息地特征对美洲狮捕食马的概率的影响。骡鹿 （Odocoileus hemionus ) 占内华达山脉参考站点上被杀死的猎物的 91%，但仅占大盆地研究区猎物的 29%。内华达山脉（ = 0.85 头鹿/周，范围= 0.44-1.3）和大盆地（ = 0.21 头鹿/周，范围= 0.00-0.43）之间的鹿平均年死亡率不同。大盆地美洲狮的饮食主要由马组成（59.6%，n = 460 个猎物；13 个人）。10 只美洲狮经常吃马，而在大盆地的另外 8 只美洲狮的饮食中，马是最丰富的猎物。在大盆地，美洲狮平均每周杀死 0.38 匹马（范围=0.00-0.94 匹马/周）。美洲狮两性对马的捕食差异是惊人的。大盆地雌性全年在所有年龄段的马匹中都加入了更多的马，而雄性美洲狮倾向于在春季和夏季利用新生幼崽，然后在冬季转为鹿。在 GLMM 模型中，与其他猎物物种相比，马被捕食的概率随着海拔、马密度和景观上骡鹿密度的降低而增加，并且在山艾树（蒿属）中比在松树中更容易发生（Pinus monophylla )-杜松 ( Juniperusosteosperma ) 森林。个体美洲狮的行为占我们预测大盆地马匹捕食的顶级模型所解释的变异的三分之一以上。在景观尺度上，美洲狮捕食不太可能限制野马种群的增长。然而，在大盆地生态系统中，两性美洲狮都成功地捕食了所有年龄段的马。此外，一些繁殖的雌性美洲狮几乎全年都依赖野马。总之，我们的数据表明美洲狮可能是野马的有效捕食者，我们之前对这种关系的一些假设应该重新评估并纳入管理和规划。© 2021 野生动物协会。