Within-individual and among-individual variation in expression of key environmentally sensitive traits, and associated variation in fitness components occurring within and between years, determine the extents of phenotypic plasticity and selection and shape population responses to changing environments. Reversible seasonal migration is one key trait that directly mediates spatial escape from seasonally deteriorating environments, causing spatio-seasonal population dynamics. Yet, within-individual and among-individual variation in seasonal migration versus residence, and dynamic associations with subsequent reproductive success, have not been fully quantified. We used novel capture-mark-recapture mixture models to assign individual European shags (Phalacrocorax aristotelis) to ‘resident’, ‘early migrant’, or ‘late migrant’ strategies in two consecutive years, using year-round local resightings. We demonstrate substantial among-individual variation in strategy within years, and directional within-individual change between years. Furthermore, subsequent reproductive success varied substantially among strategies, and relationships differed between years; residents and late migrants had highest success in the 2 years, respectively, matching the years in which these strategies were most frequently expressed. These results imply that migratory strategies can experience fluctuating reproductive selection, and that flexible expression of migration can be partially aligned with reproductive outcomes. Plastic seasonal migration could then potentially contribute to adaptive population responses to currently changing forms of environmental seasonality.

中文翻译：

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季节性迁徙协变的个体间和个体内变异以及部分候鸟随后的繁殖成功

关键环境敏感性状表达的个体内和个体间变异，以及年份内和年份之间发生的适应性成分的相关变异，决定了表型可塑性和选择的程度，并塑造了种群对不断变化的环境的反应。可逆的季节性迁徙是直接调节季节性恶化环境的空间逃逸的关键特征，导致时空种群动态。然而，个体内部和个体之间季节性迁徙与居住的差异，以及与随后繁殖成功的动态关联，尚未得到充分量化。我们使用新颖的捕获-标记-重新捕获混合模型，通过全年的当地重新观察，连续两年将个体欧洲鸬鹚（Phalacrocorax aristotelis）分配为“居民”、“早期移民”或“晚期移民”策略。我们证明了几年内个体间策略的巨大差异，以及几年间个体内部的方向性变化。此外，随后的繁殖成功率在不同策略之间存在很大差异，而且不同年份之间的关系也不同。居民和晚期移民分别在这两年中取得了最高的成功，与这些策略最常表达的年份相匹配。这些结果意味着迁徙策略可能会经历波动的生殖选择，并且迁徙的灵活表达可能与生殖结果部分一致。塑料季节性迁移可能有助于人口对当前不断变化的环境季节性形式的适应性反应。