Abstract Human enterprise has modified ecosystem processes through direct and indirect alteration of native predators' distribution and abundance. For example, human activities subsidize food, water, and shelter availability to generalist predators whose subsequent increased abundance impacts lower trophic-level prey species. The common raven (Corvus corax; hereafter, raven) is an avian scavenger and predator, native to the northern hemisphere, that can become invasive when subsidized. Raven populations are increasing at unprecedented rates in many regions globally. Information regarding scale of impact and potential ecological thresholds is needed to guide conservation actions aimed at reducing adverse effects on sensitive prey. We conducted a multi-part analysis to investigate broad-scale variation in raven densities and impacts on nesting greater sage-grouse (Centrocercus urophasianus), an indicator species for sagebrush ecosystems in western North America. We estimated raven densities using >16,000 point surveys over 10 years within the Great Basin, USA, and examined associations with anthropogenic and environmental covariates. Average density was 0.54 ravens km−2 (95% CI: 0.42–0.70), with higher densities at lower relative elevations comprising increased agriculture and development. We then used a reduced dataset to estimate the effect of raven density on sage-grouse nest survival (nests = 737). We identified negative impacts to nesting sage-grouse, especially where raven density exceeded ~0.40 km−2, a potential ecological threshold. We mapped regions where elevated raven densities were predicted to depress sage-grouse population growth in the absence of compensatory demographic responses from other sage-grouse life-history stages, and found ~64% of sage-grouse breeding areas were adversely impacted by high raven density.

中文翻译：

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入侵的本地捕食者对北美大盆地不断变化的鸟类群落中敏感的本地猎物物种的广泛影响

摘要 人类企业通过直接和间接改变本地捕食者的分布和丰度来改变生态系统过程。例如，人类活动为一般捕食者提供食物、水和住所的补贴，这些捕食者随后增加的丰度会影响低营养级的猎物物种。普通乌鸦（Corvus corax；以下简称乌鸦）是一种鸟类清道夫和捕食者，原产于北半球，在获得补贴后会变得具有侵略性。在全球许多地区，乌鸦种群正以前所未有的速度增长。需要有关影响规模和潜在生态阈值的信息来指导旨在减少对敏感猎物的不利影响的保护行动。我们进行了一项多部分分析，以调查乌鸦密度的广泛变化以及对筑巢大鼠尾草松鸡（Centrocercus urophasianus）的影响，这是北美西部山艾树生态系统的指示物种。我们在美国大盆地 10 年内使用 >16,000 点调查估计了乌鸦密度，并检查了与人为和环境协变量的关联。平均密度为 0.54 只乌鸦 km-2（95% CI：0.42–0.70），在较低的相对海拔处密度较高，包括农业和发展的增加。然后我们使用减少的数据集来估计乌鸦密度对鼠尾草巢生存的影响（巢 = 737）。我们确定了对筑巢鼠尾草的负面影响，特别是在乌鸦密度超过约 0.40 km-2 的地方，这是一个潜在的生态阈值。