Data from: Predator-rodent-plant interactions along a coast-inland gradient in Fennoscandian tundra

Spatial variation in the strength of trophic cascades in arctic tundra has been related to flows of subsidies across ecosystem boundaries. Here, we ask whether the input of marine subsidies in tundra systems would cause spatial variation in the strength of rodent-plant interactions between coastal areas, where predators have access to marine-derived resources, and non-subsidized inland areas of northern Fennoscandia. We present a detailed evaluation of predator-rodent-vegetation interactions along a coast-inland gradient, during the 2011 rodent outbreak and the two following decline years, by using direct assessments of rodent impacts and tracing of marine-derived nutrients in the food web. Our results revealed that the main rodent predator during summer, the long-tailed jaeger Stercorarius longicaudus, did not benefit from marine resources while breeding (relative dietary proportion in chicks’ diet = 0-3%). Contrary to this pattern, parasitic jaegers S. parasiticus, bred exclusively near the coast and preyed effectively on both marine resources (41% of chicks’ diet) and rodents (12%). Mammalian predators also showed a higher activity during winter near the coast. Despite overall higher predator numbers, no evidence was found for lower rodent population growth rates during the three monitoring summers and for weaker rodent grazing impacts in the coastal area. Instead, we documented pronounced damages caused by lemmings and voles on bryophytes and vascular plants, especially dwarf shrubs (e.g., Vaccinum myrtillus) all along the coast-inland gradient. Taken together, our results did not support the hypothesis that marine subsidies would trigger a trophic cascade in coastal tundra areas of northern Fennoscandia during a major rodent outbreak, probably due to a low diversity of marine-subsidized predators in the region. Comparative observational and experimental studies at large spatial scales in various arctic regions are absolutely necessary for a better understanding of factors causing regional variations in the functioning of arctic food webs.

北极苔原（arctic tundra）营养级联效应（trophic cascades）强度的空间变异，与跨生态系统边界（ecosystem boundaries）的外源物质流动密切相关。本研究旨在探讨：在芬诺斯坎底亚北部，捕食者可获取海洋来源资源的沿海区域，与未受海洋外源补贴（marine subsidies）的内陆区域之间，苔原生态系统中的海洋外源输入是否会导致啮齿动物-植物相互作用强度产生空间差异。
本研究于2011年啮齿动物大暴发及其后续两年的种群衰减期内，通过直接评估啮齿动物的影响，并追踪食物网（food web）中的海洋来源营养物质，对沿海-内陆梯度上的捕食者-啮齿动物-植被相互作用进行了详尽的评估。

研究结果显示，夏季主要的啮齿动物捕食者——长尾贼鸥（Stercorarius longicaudus）在繁殖期间并未从海洋资源中获益（雏鸟日粮中的相对占比为0%~3%）。与此相反，寄生贼鸥（Stercorarius parasiticus）仅在沿海区域繁殖，且能有效捕食海洋资源（占雏鸟日粮的41%）与啮齿动物（占12%）。哺乳动物捕食者在冬季的活动强度也在沿海区域更高。尽管沿海区域的捕食者总体数量更多，但在三年监测的夏季中，并未发现啮齿动物种群增长率更低的证据，也未观测到沿海区域啮齿动物的放牧影响更弱的迹象。

相反，我们记录到旅鼠（lemmings）与田鼠（voles）对苔藓植物（bryophytes）和维管植物（vascular plants），尤其是矮灌木（如越橘Vaccinium myrtillus）造成了显著损害，且这种损害沿沿海-内陆梯度普遍存在。综合来看，本研究结果不支持‘在芬诺斯坎底亚北部沿海苔原区域的啮齿动物大暴发期间，海洋外源补贴会触发营养级联效应’这一假说，其原因可能是该区域依赖海洋外源物质的捕食者多样性较低。为更好地理解导致北极食物网功能区域变异的因素，在不同北极区域开展大空间尺度的对比观测与实验研究是极为必要的。