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Can Reindeer Overabundance Cause a Trophic Cascade?

机译：驯鹿过多会导致营养级联吗？

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The region Finnmark, in northernmost Europe, harbors dense populations of semi-domestic reindeer of which some exhibit characteristics of overabundance. Whereas overabundance is evident in terms of density-dependent reductions in reindeer body mass, population growth and abundance of forage plants, claims have been made that this reindeer overabundance also has caused a trophic cascade. These claims are based on the main premise that reindeer overgrazing negatively impacts small-sized, keystone tundra herbivores. We tested this premise by a large-scale study in which the abundance of small rodents, hares and ptarmigans was indexed across reindeer management districts with strong differences in stocking densities. We examined the scale-dependent relations between reindeer, vegetation and these small-sized herbivores by employing a spatially hierarchical sampling design within the management districts. A negative impact of reindeer on ptarmigan, probably as a result of browsing reducing tall Salix, was indicated. However, small rodents (voles and lemmings), which are usually the keystone herbivores in the plant-based tundra food web, were not negatively impacted. On the contrary, there was a strong positive relationship between small rodents and reindeer, both at the scale of landscape areas and local patches, with characteristics of snow-bed vegetation, suggesting facilitation between Norwegian lemmings and reindeer. We conclude that the recent dampening of the vole and lemming population cycle with concurrent declines of rodent predators in northernmost Europe were not caused by large herbivore overgrazing.
机译：在欧洲最北端的芬马克（Finnmark）地区拥有半驯鹿的密集种群，其中一些驯鹿具有过剩的特征。尽管驯鹿体重，种群增长和饲草植物密度的密度依赖性降低明显表明了过量，但有人声称这种驯鹿过量也造成了营养级联。这些主张基于主要前提，即驯鹿过度放牧会对小型梯形苔原食草动物产生负面影响。我们通过大规模研究对这一前提进行了测试，在该研究中，在驯鹿管理区索引了许多小型啮齿动物，野兔和雷鸟，它们的放养密度差异很大。我们通过在管理区域内采用空间分层抽样设计，研究了驯鹿，植被与这些小型食草动物之间的尺度相关关系。有人指出，驯鹿对雷鸟有负面影响，这可能是浏览减少了柳柳的结果。但是，小啮齿动物（田鼠和旅鼠）通常不会受到负面影响，它们通常是植物性苔原食物网中的主要食草动物。相反，小啮齿动物和驯鹿之间在景观区域和局部斑块上都具有很强的正相关关系，具有雪床植被的特征，这表明挪威旅鼠和驯鹿之间的相互促进。我们得出的结论是，最近在欧洲最北端的田鼠种群减少和圈养种群周期减少，同时啮齿动物捕食者数量下降，并不是由大量草食动物过度放牧引起的。

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