Data from: Non-linear effect of sea ice: Spectacled Eider survival declines at both extremes of the ice spectrum

Understanding the relationship between environmental factors and vital rates is an important step in predicting a species’ response to environmental change. Species associated with sea ice are of particular concern because sea ice is projected to decrease rapidly in polar environments with continued levels of greenhouse gas emissions. The relationship between sea ice and the vital rates of the Spectacled Eider, a threatened species that breeds in Alaska and Russia and winters in the Bering Sea, appears to be complex. While severe ice can impede foraging for benthic prey, ice also suppresses wave action and provides a platform on which eiders roost, thereby reducing thermoregulation costs. We analyzed a 23-year mark-recapture dataset for Spectacled Eiders nesting on Kigigak Island in western Alaska, and tested survival models containing different ice and weather-related covariates. We found that much of the variation in eider survival could be explained by the number of days per year with >95% sea ice concentration at the Bering Sea core wintering area. Furthermore, the data supported a quadratic relationship with sea ice rather than a linear one, indicating that intermediate sea ice concentrations were optimal for survival. We then used matrix population models to project population trajectories using General Circulation Model (GCM) outputs of daily sea ice cover. GCMs projected reduced sea ice at the wintering area by year 2100 under a moderated emissions scenario (RCP 4.5) and nearly ice-free conditions under an unabated emissions scenario (RCP 8.5). Under RCP 4.5, stochastic models projected an increase in population size until 2069 coincident with moderate ice conditions, followed by a decline in population size as ice conditions shifted from intermediate to mostly ice-free. Under RCP 8.5, eider abundance increased until 2040 and then decreased to near extirpation toward the end of the century as the Bering Sea became ice-free.

探明环境因子与种群生命率之间的关联，是预测物种对环境变化响应的核心环节。与海冰伴生的物种尤其值得关注，因为在温室气体排放持续维持当前水平的背景下，极地环境中的海冰预计将快速消退。白眶绒鸭（Spectacled Eider）是受胁物种，其繁殖地位于阿拉斯加与俄罗斯，越冬地则在白令海，该物种的海冰与生命率之间的关系看似颇为复杂：重度海冰会阻碍底栖猎物的觅食活动，但同时也能抑制波浪作用，并为绒鸭提供休憩平台，从而降低体温调节成本。我们分析了阿拉斯加西部基吉加克岛筑巢的白眶绒鸭长达23年的标记重捕数据集，并针对包含不同海冰与气象相关协变量的生存模型开展了检验。研究发现，绒鸭生存的大部分变异可通过白令海核心越冬区每年海冰浓度高于95%的天数来解释。此外，数据支持海冰与生存之间存在二次关系，而非线性关系，这表明中等海冰浓度对生存最为有利。随后，我们借助矩阵种群模型，结合通用环流模型（General Circulation Model, GCM）输出的每日海冰覆盖数据，对种群动态轨迹进行了预测。在适度排放情景（RCP 4.5）下，通用环流模型预计到2100年越冬区海冰将大幅减少；而在无减排的持续排放情景（RCP 8.5）下，越冬区将几乎无海冰覆盖。在RCP 4.5情景下，随机模型预计种群数量将在2069年前随中等海冰条件持续增长，随后随着海冰从中等状态转向近乎无冰，种群数量开始下降。在RCP 8.5情景下，绒鸭种群数量在2040年前增长，之后随着白令海海冰完全消失，到本世纪末降至近乎局部灭绝的水平。