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 predator 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 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 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 characterised by pulsed resources.

中文翻译：

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北极苔原鸟类捕食者之间的资源分配

种间竞争可以在构建生态群落中发挥关键作用。北极苔原是一个生产力低下的生态系统，支持简单的食物网，但有几种捕食者经常以同一种猎物为食，旅鼠以种群数量大幅波动而闻名。我们研究了减少公会内部竞争和允许以脉冲资源（棕色和有领旅鼠）为食的四种鸟类掠食者（雪鸮、白鸥、粗腿鹰和长尾猎豹）共存的机制。我们比较了捕食者消耗的猎物的大小和种类，以查看是否发生了资源分配。我们还验证了筑巢区的空间隔离是否是另一种允许共存的机制。最后，我们测试了雪鸮（一种占主导地位的侵入性物种）是否消失，就猎物的大小和所用的筑巢面积而言，触发了对最小的捕食者 jaeger 的竞争性释放。我们在 14 年的时间里监测了加拿大拜洛特岛捕食者的繁殖和旅鼠的数量。我们绘制了它们的筑巢地点并收集了反流颗粒以恢复旅鼠下颌骨，这些下颌骨用于推断猎物的种类和大小。消耗的旅鼠的大小因物种而异，最大的捕食者消耗最大的旅鼠，而最小的捕食者则消耗最小的旅鼠。尽管与海鸥和鹰相比，猫头鹰和猎犬消耗的棕色旅鼠相对更多，但与它们的可用性相比，所有捕食者都比棕色旅鼠消耗更多的项圈。Jaegers 在没有猫头鹰的情况下消耗了比有猫头鹰更大的旅鼠，这暗示了短期的竞争性释放。我们发现捕食者的筑巢区域有中到低的重叠，并且没有证据表明它们在没有猫头鹰的情况下会扩大，这表明空间分布是由特定物种的栖息地偏好引起的。在这些鸟类捕食者之间分配食物资源的主要机制是空间隔离，其次是猎物大小和物种。然而，我们发现有证据表明食物竞争仍然存在，并导致公会最小捕食者的利基转变。因此，种间竞争可能是以脉冲资源为特征的简单、低生产力食物网中的普遍力量。在这些鸟类捕食者之间分配食物资源的主要机制是空间隔离，其次是猎物的大小和物种。然而，我们发现有证据表明食物竞争仍然存在，并导致公会最小捕食者的利基转变。因此，种间竞争可能是以脉冲资源为特征的简单、低生产力食物网中的普遍力量。在这些鸟类捕食者之间分配食物资源的主要机制是空间隔离，其次是猎物大小和物种。然而，我们发现有证据表明食物竞争仍然存在，并导致公会最小捕食者的利基转变。因此，种间竞争可能是以脉冲资源为特征的简单、低生产力食物网中的普遍力量。