(Table 1) Nesting characteristics of greater snow geese (Chen caerulescens atlanticus) on Bylot Island between 1995-2005

1. Habitat heterogeneity and predator behaviour can strongly affect predator-prey interactions but these factors are rarely considered simultaneously, especially when systems encompass multiple predators and prey.
2. In the Arctic, greater snow geese Anser caerulescens atlanticus L. nest in two structurally different habitats: wetlands that form intricate networks of water channels, and mesic tundra where such obstacles are absent. In this heterogeneous environment, goose eggs are exposed to two types of predators: the arctic fox Vulpes lagopus L. and a diversity of avian predators. We hypothesized that, contrary to birds, the hunting ability of foxes would be impaired by the structurally complex wetland habitat, resulting in a lower predation risk for goose eggs.
3. In addition, lemmings, the main prey of foxes, show strong population cycles. We thus further examined how their fluctuations influenced the interaction between habitat heterogeneity and fox predation on goose eggs.
4. An experimental approach with artificial nests suggested that foxes were faster than avian predators to find unattended goose nests in mesic tundra whereas the reverse was true in wetlands. Foxes spent 3-5 times more time between consecutive attacks on real goose nests in wetlands than in mesic tundra. Their attacks on goose nests were also half as successful in wetlands than in mesic tundra whereas no difference was found for avian predators.
5. Nesting success in wetlands (65%) was higher than in mesic tundra (56%) but the difference between habitats increased during lemming crashes (15%) compared to other phases of the cycle (5%). Nests located at the edge of wetland patches were also less successful than central ones, suggesting a gradient in accessibility of goose nests in wetlands for foxes.
6. Our study shows that the structural complexity of wetlands decreases predation risk from foxes but not avian predators in arctic-nesting birds. Our results also demonstrate that cyclic lemming populations indirectly alter the spatial distribution of productive nests due to a complex interaction between habitat structure, prey-switching and foraging success of foxes.

1. 生境异质性（habitat heterogeneity）与捕食者行为均可显著影响捕食者-猎物相互作用（predator-prey interactions），但此类因素鲜少被同时纳入考量，在包含多种捕食者与猎物的生态系统中尤为如此。
2. 在北极地区，大雪雁（Anser caerulescens atlanticus L.）的筑巢生境分为两类结构迥异的类型：一是形成复杂交错水道网络的湿地，二是无此类障碍物的中湿苔原（mesic tundra）。在这片异质性生境中，雁卵面临两类捕食者：北极狐（Vulpes lagopus L.）与多种鸟类捕食者（avian predators）。我们提出假说：与鸟类捕食者不同，北极狐的捕猎能力会受到结构复杂的湿地生境抑制，从而使雁卵面临更低的捕食风险。
3. 此外，作为北极狐主要猎物的旅鼠（lemmings）存在显著的种群周期波动。我们进一步探究了旅鼠的种群波动如何影响生境异质性与狐狸对雁卵捕食之间的相互作用。
4. 采用人工巢开展的实验表明，在中湿苔原中，北极狐比鸟类捕食者更快发现无人值守的雁巢；而在湿地中则恰好相反。相较于中湿苔原，湿地内真实雁巢的相邻捕食间隔时长为前者的3~5倍。北极狐在湿地的捕食成功率仅为中湿苔原的一半，而鸟类捕食者的捕食成功率则未表现出生境差异。
5. 湿地内的筑巢成功率（65%）高于中湿苔原（56%），但在旅鼠种群崩溃（lemming crashes）阶段，两类生境的筑巢成功率差异（15%）较种群周期的其他阶段（5%）更为显著。位于湿地斑块边缘的巢筑巢成功率也低于中心区域的巢，这表明湿地内雁巢对北极狐的可及性存在空间梯度。
6. 本研究表明，湿地的结构复杂性可降低北极筑巢鸟类面临的北极狐捕食风险，但对鸟类捕食者无此效应。我们的研究结果还证实，由于生境结构、猎物转换（prey-switching）行为与北极狐觅食成功率之间存在复杂的相互作用，周期性波动的旅鼠种群会间接改变高成功率筑巢地的空间分布。