Populations of Pacific common eiders (Somateria mollissima v‐nigrum) on the Yukon‐Kuskokwim Delta (YKD) in western Alaska declined by 50–90% from 1957 to 1992 and then stabilized at reduced numbers from the early 1990s to the present. We investigated the underlying processes affecting their population dynamics by collection and analysis of demographic data from Pacific common eiders at 3 sites on the YKD (1991–2004) for 29 site‐years. We examined variation in components of reproduction, tested hypotheses about the influence of specific ecological factors on life‐history variables, and investigated their relative contributions to local population dynamics. Reproductive output was low and variable, both within and among individuals, whereas apparent survival of adult females was high and relatively invariant (0.89 ± 0.005). All reproductive parameters varied across study sites and years. Clutch initiation dates ranged from 4 May to 28 June, with peak (modal) initiation occurring on 26 May. Females at an island study site consistently initiated clutches 3–5 days earlier in each year than those on 2 mainland sites. Population variance in nest initiation date was negatively related to the peak, suggesting increased synchrony in years of delayed initiation. On average, total clutch size (laid) ranged from 4.8 to 6.6 eggs, and declined with date of nest initiation. After accounting for partial predation and non‐viability of eggs, average clutch size at hatch ranged from 2.0 to 5.8 eggs. Within seasons, daily survival probability (DSP) of nests was lowest during egg‐laying and late‐initiation dates. Estimated nest survival varied considerably across sites and years (mean = 0.55, range: 0.06–0.92), but process variance in nest survival was relatively low (0.02, CI: 0.01–0.05), indicating that most variance was likely attributed to sampling error. We found evidence that observer effects may have reduced overall nest survival by 0.0–0.36 across site‐years. Study sites with lower sample sizes and more frequent visitations appeared to experience greater observer effects. In general, Pacific common eiders exhibited high spatio‐temporal variance in reproductive components. Larger clutch sizes and high nest survival at early initiation dates suggested directional selection favoring early nesting. However, stochastic environmental effects may have precluded response to this apparent selection pressure. Our results suggest that females breeding early in the season have the greatest reproductive value, as these birds lay the largest clutches and have the highest probability of successfully hatching. We developed stochastic, stage‐based, matrix population models that incorporated observed spatio‐temporal (process) variance and co‐variation in vital rates, and projected the stable stage distribution () and population growth rate (λ). We used perturbation analyses to examine the relative influence of changes in vital rates on λ and variance decomposition to assess the proportion of variation in λ explained by process variation in each vital rate. In addition to matrix‐based λ, we estimated λ using capture–recapture approaches, and log‐linear regression. We found the stable age distribution for Pacific common eiders was weighted heavily towards experienced adult females (≥4 yr of age), and all calculations of λ indicated that the YKD population was stable to slightly increasing (λ^matrix = 1.02, CI: 1.00–1.04); λ^{reverse‐capture–recapture} = 1.05, CI: 0.99–1.11; λ^log‐linear = 1.04, CI: 0.98–1.10). Perturbation analyses suggested the population would respond most dramatically to changes in adult female survival (relative influence of adult survival was 1.5 times that of fecundity), whereas retrospective variation in λ was primarily explained by fecundity parameters (60%), particularly duckling survival (42%). Among components of fecundity, sensitivities were highest for duckling survival, suggesting this vital rate may be a current restriction to further population growth. Increasing adult survival would have the largest positive effects on population growth, but practical ways to influence this vital rate are currently limited. Given that eider laying dates and nest fates may be closely tied to those of sympatrically nesting species, we hypothesize that management actions facilitating early nesting and targeting other species (e.g., increasing overall potential for predator‐swamping) may have positive, concurrent effects on nesting common eiders. If enhancing population growth is the objective and assuming the population is not currently at carrying capacity, we recommend an adaptive management approach. This approach would begin with focused efforts towards increasing reproductive output, with particular emphasis on strategies to increase both fecundity and nest survival, such as predator control on breeding grounds, followed by evaluation of population response. However, we conducted our modeling efforts under assumptions of density independence, whereas density‐dependent mechanisms may have played an important role in the historic decline and subsequent stabilization of our population at a new, lower equilibrium. In an adaptive‐management context, our results can be used to test additional (density‐related) models; our predicted response would be compared with actual population response to prescribed management manipulations. Failure of the population to positively respond to increases in vital rates and negative correlations among vital rates would serve as evidence of density‐dependent regulation. Rejection of the density‐independent model would support management actions focused on habitat improvement. © 2012 The Wildlife Society.

中文翻译：

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阿拉斯加育空地区库斯科维克三角洲繁殖太平洋常见绒毛的种群生态

太平洋常见绒鸭（Somateria mollissima v-nigrum）的种群）在阿拉斯加西部的育空地区-库斯科科姆三角洲（YKD）从1957年到1992年下降了50-90％，然后从1990年代初期到现在稳定下来。我们通过收集和分析YKD（1991-2004年）3个地点（历时29年）的太平洋常见绒毛人口统计数据，调查了影响其人口动态的潜在过程。我们研究了繁殖成分的变化，检验了有关特定生态因素对生活史变量的影响的假设，并调查了它们对当地人口动态的相对贡献。个体内部和个体之间的生殖产量均较低且易变，而成年女性的表观存活率较高且相对不变（0.89±0.005）。不同研究地点和年份的所有生殖参数都不同。离合器的启动日期为5月4日至6月28日，高峰（模态）启动于5月26日发生。与两个大陆地点相比，在岛上研究地点的雌性每年持续提早3-5天抓紧离合器。巢启动日期的种群差异与峰值呈负相关，表明在延迟启动的年份中同步性增加。平均而言，离合器的总大小（产蛋量）在4.8到6.6个卵之间，并且随着开始筑巢的日期而下降。考虑到鸡蛋的部分捕食和不生存能力后，孵化时的平均离合大小为2.0至5.8个鸡蛋。在季节内，在产卵期和后期启动期间，巢的日生存概率（DSP）最低。不同地点和年份的估计巢生存率差异很大（平均值= 0.55，范围：0.06-0.92），但巢生存的过程方差相对较低（0.02，CI：0.01–0.05），表明大多数方差可能归因于采样误差。我们发现有证据表明观察者的影响可能使整个站点年的整体巢生存减少了0.0-0.36。具有较小样本量和更频繁访问的研究站点似乎经历了更大的观察者效果。一般而言，太平洋常见的绒毛在生殖成分上表现出很高的时空差异。较大的离合器尺寸和较高的早期成活率表明建议选择方向有利于早期筑巢。但是，随机的环境影响可能会阻止对这种表观选择压力的反应。我们的结果表明，本季节早期繁殖的雌性具有最大的繁殖价值，因为这些鸟会抓住最大的离合器，并且成功孵化的可能性最高。我们开发了随机的，基于阶段的矩阵人口模型，该模型结合了观察到的时空（过程）方差和生命率的协方差，并预测了稳定的阶段分布（）和人口增长率（λ）。我们使用扰动分析来检查生命率变化对λ的相对影响，并使用方差分解来评估每个生命率中过程变化所解释的λ变化的比例。除了基于矩阵的λ之外，我们还使用捕获－捕获方法和对数线性回归来估计λ。我们发现太平洋普通鸭绒的稳定年龄分布对有经验的成年女性（≥4岁）具有很大的权重，并且所有λ的计算都表明YKD群体稳定到略有增加（λ^矩阵 = 1.02，CI：1.00– 1.04）；λ^{反向捕获-捕获} = 1.05，CI：0.99–1.11; λ^对数线性 = 1.04，CI：0.98-1.10）。摄动分析表明，种群对成年女性存活率的变化反应最为显着（成年存活率的相对影响是繁殖力的1.5倍），而λ的回顾性变化主要由繁殖力参数（60％）解释，特别是小鸭存活率（42） ％）。在繁殖力的各个组成部分中，对小鸭生存的敏感性最高，这表明该生命率可能是目前限制种群进一步增长的因素。成人成活率的提高将对人口增长产生最大的积极影响，但是目前影响这一生命率的实际方法是有限的。鉴于绒毛的定居日期和巢境命运可能与同巢筑巢物种的息息相关，我们假设，有利于及早筑巢和针对其他物种的管理行动（例如，增加捕食者-沼泽沼泽的总体潜力）可能对共同的绒鸭有积极的，同时的影响。如果以提高人口增长为目标，并假设当前人口尚未达到承载能力，则建议采用适应性管理方法。这种方法将首先集中精力增加生殖产量，特别强调增加繁殖力和巢生存率的战略，例如在繁殖地控制捕食者，然后评估种群反应。但是，我们在密度独立的假设下进行了建模工作，而依赖密度的机制可能在历史性下降和随后的人口稳定在新的较低平衡中起了重要作用。在自适应管理的情况下，我们的结果可用于测试其他（与密度有关）的模型；我们的预测响应将与对规定管理操作的实际人群响应进行比较。人口不能对生命率的增加做出积极反应，而生命率之间的负相关也可以作为密度依赖性调节的证据。拒绝密度无关的模型将支持专注于栖息地改善的管理行动。©2012野生动物协会。我们的预测响应将与对规定管理操作的实际人群响应进行比较。人口不能对生命率的增加做出积极反应，而生命率之间的负相关也可以作为密度依赖性调节的证据。拒绝密度无关的模型将支持专注于栖息地改善的管理行动。©2012野生动物协会。我们的预测响应将与对规定管理操作的实际人群响应进行比较。人口不能对生命率的增加做出积极反应，而生命率之间的负相关也可以作为密度依赖性调节的证据。拒绝密度无关的模型将支持专注于栖息地改善的管理行动。©2012野生动物协会。