Seyer Yannick, Gauthier Gilles, Fauteux Dominique, Therrien Jean-François
Department of Biology and Centre d'études nordiques, Université Laval, Québec, QC, Canada.
Canadian Museum of Nature, Ottawa, ON, Canada.
J Anim Ecol. 2020 Dec;89(12):2934-2945. doi: 10.1111/1365-2656.13346. Epub 2020 Oct 7.
Interspecific competition can play a key role in structuring ecological communities. The Arctic tundra is a low productivity ecosystem supporting simple food webs, but several predators often feed on the same prey species, lemmings, known for their large-amplitude population fluctuations. We examined mechanisms involved in reducing intra-guild competition and allowing coexistence of four avian predators (snowy owls, glaucous gulls, rough-legged hawks and long-tailed jaegers) feeding on a pulsed resource (brown and collared lemmings). We compared the size and species of prey consumed by predators to see if resource partitioning occurred. We also verified if spatial segregation in nesting areas could be another mechanism allowing coexistence. Finally, we tested if the absence of the snowy owl, a dominant and irruptive species, triggered a competitive release on the smallest predator, the jaeger, with respect to prey size and nesting area used. We monitored the breeding of predators and lemming abundance over a 14-year period on Bylot Island, Canada. We mapped their nesting sites and collected regurgitation pellets to recover lemming mandibles, which were used to infer prey species and size. The size of lemmings consumed varied among species with the largest predators consuming the largest lemmings and the smallest predators consuming the smallest lemmings. All predators consumed more collared than brown lemmings compared to their availability although owls and jaegers consumed relatively more brown lemmings compared to gulls and hawks. Jaegers consumed larger lemmings in the absence of owls than in their presence, suggestive of a short-term competitive release. We found moderate to low overlap in nesting areas among predators and no evidence of their expansion in the absence of owls, suggesting that spatial distribution is caused by species-specific habitat preferences. The main mechanism to partition food resources among these avian predators is spatial segregation, and secondarily prey size and species. However, we found evidence that food competition is still present and leads to a niche shift in the smallest predator of the guild. Interspecific competition may thus be a pervasive force in simple, low productivity food webs characterized by pulsed resources.
种间竞争在构建生态群落中可能起着关键作用。北极苔原是一个生产力低下的生态系统，支持着简单的食物网，但几种捕食者常常以同一种猎物——旅鼠为食，旅鼠以其大幅度的种群波动而闻名。我们研究了减少同域竞争并使四种以脉冲式资源（棕旅鼠和环颈旅鼠）为食的鸟类捕食者（雪鸮、白鸥、矛隼和长尾贼鸥）共存的机制。我们比较了捕食者所消耗猎物的大小和种类，以查看是否发生了资源划分。我们还验证了筑巢区域的空间隔离是否可能是另一种允许共存的机制。最后，我们测试了作为优势且具有爆发性的物种雪鸮的缺失，是否会引发最小的捕食者贼鸥在猎物大小和使用的筑巢区域方面的竞争释放。我们在加拿大的比洛特岛对捕食者的繁殖和旅鼠数量进行了为期14年的监测。我们绘制了它们的筑巢地点，并收集反刍颗粒以找回旅鼠的下颌骨，用于推断猎物的种类和大小。不同物种所消耗的旅鼠大小各不相同，最大的捕食者消耗最大的旅鼠，最小的捕食者消耗最小的旅鼠。与棕旅鼠的可获得性相比，所有捕食者消耗的环颈旅鼠都更多，尽管与鸥和隼相比，鸮和贼鸥消耗的棕旅鼠相对更多。在没有鸮的情况下，贼鸥消耗的旅鼠比有鸮时更大，这表明存在短期的竞争释放。我们发现捕食者之间筑巢区域的重叠程度为中度到低度，并且没有证据表明在没有鸮的情况下它们的筑巢区域会扩大，这表明空间分布是由物种特定的栖息地偏好引起的。这些鸟类捕食者之间划分食物资源的主要机制是空间隔离，其次是猎物大小和种类。然而，我们发现有证据表明食物竞争仍然存在，并导致了该同域中最小捕食者的生态位转移。因此，种间竞争可能是在以脉冲式资源为特征的简单、低生产力食物网中一种普遍存在的力量。
