Invasive alien species pose one of the greatest threats to global biodiversity. In parts of Europe, introduced eastern grey squirrels ( Sciurus carolinensis ) have caused regional extinctions of the native red squirrel ( Sciurus vulgaris ). However, exposure to pine martens ( Martes martes ) has been demonstrated to reverse the competitive outcome between red and grey squirrels. The mechanism whereby this effect occurs remains unclear. It is hypothesised that direct predation, facilitated by a lack of behavioural response, is the mechanism driving this relationship. We review the literature and reanalyse a new dataset to provide further data on the occurrence of both squirrel species in the scats of pine marten. Both squirrel species occurred in the scats of pine marten confirming its role as a predator of these species. Predation of grey squirrels was significantly higher than red squirrels and was recorded only in spring and summer. Our review provides evidence for the mechanism driving the current decline in grey squirrels in Ireland and Scotland and supports the hypothesis that in the presence of a shared predator, direct predation influences the outcome of species interactions between native red and non-native grey squirrels.

中文翻译：

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松貂捕食红松鼠和灰松鼠的动态

外来入侵物种是对全球生物多样性的最大威胁之一。在欧洲部分地区，引进的东部灰松鼠 (Sciurus carolinensis) 已导致本地红松鼠 (Sciurus vulgaris) 的区域性灭绝。然而，暴露于松鼠 (Martes martes) 已被证明可以扭转红松鼠和灰松鼠之间的竞争结果。这种效应发生的机制尚不清楚。据推测，由于缺乏行为反应而促进的直接捕食是驱动这种关系的机制。我们回顾了文献并重新分析了一个新的数据集，以提供关于松貂粪便中两种松鼠物种发生的进一步数据。这两种松鼠物种都出现在松貂的粪便中，证实了松鼠作为这些物种的捕食者的作用。灰松鼠的捕食率明显高于红松鼠，仅在春季和夏季有记录。我们的评论为驱动爱尔兰和苏格兰灰松鼠目前数量下降的机制提供了证据，并支持以下假设：在存在共同捕食者的情况下，直接捕食会影响本地红松鼠和非本地灰松鼠之间物种相互作用的结果。