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.北极苔原营养级联（trophic cascade）强度的空间异质性，与跨生态系统边界的外源补贴（subsidies）流动密切相关。本研究旨在探讨：在芬诺斯坎底亚北部，苔原生态系统中的海洋外源补贴输入，是否会在两类区域间造成啮齿动物-植物相互作用强度的空间异质性——一类是捕食者可获取海洋来源资源的沿海区域，另一类是无外源补贴的内陆区域。本研究于2011年啮齿动物种群暴发（rodent outbreak）及其后的两年种群衰减期内，通过直接评估啮齿动物的影响以及追踪食物网（food web）中的海洋来源营养物，对沿海-内陆梯度上的捕食者-啮齿动物-植被相互作用（predator-rodent-vegetation interactions）进行了详尽解析。研究结果显示：夏季啮齿动物的主要捕食者——长尾贼鸥（long-tailed jaeger, *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，中贼鸥（parasitic jaeger, *Stercorarius parasiticus*）仅在沿海区域繁殖，且可有效捕食海洋资源（占雏鸟日粮的41%）与啮齿动物（占12%）。哺乳类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数量更多，但在为期三年的监测夏季中，并未发现啮齿动物种群增长率更低的证据，也未发现沿海区域啮齿动物的取食影响更弱的迹象。反之，本研究观测到：在整条沿海-内陆梯度上，旅鼠（lemmings）与田鼠（voles）对苔藓植物（bryophytes）和维管植物（vascular plants）、尤其是欧洲越橘（*Vaccinum myrtillus*）这类矮灌木（dwarf shrubs）造成了显著危害。综合来看，本研究结果不支持该假说：即在芬诺斯坎底亚北部沿海苔原发生大规模啮齿动物暴发期间，海洋外源补贴会触发营养级联效应，这一结果可能源于该区域依赖海洋补贴的捕食者多样性较低。为更深入理解导致北极食物网功能存在区域异质性（regional variations）的驱动因素，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。