Department of Biology, 238 Gilmer Hall, University of Virginia, Charlottesville, Virginia 22904, USA.
Ecology. 2011 Jun;92(6):1236-46. doi: 10.1890/11-0133.1.
Species with partial migration, where a portion of a population migrates and the other remains residential, provide the opportunity to evaluate conditions for migration and test mechanisms influencing migratory decisions. We conducted a five-year study of two populations of red-spotted newts (Notophthalmus viridescens), composed of individuals that either remain as residents in the breeding pond over the winter or migrate to the terrestrial habitat. We used multistate mark-recapture methods to (1) test for differences in survival probability between migrants and residents, (2) determine if migrants breed every year or skip opportunities for reproduction, and (3) estimate the frequency of individuals switching migratory tactic. We used estimates of life history parameters from the natural populations in combination with previous experimental work to evaluate processes maintaining partial migration at the population level and to assess mechanisms influencing the decision to migrate. Based on capture-recapture information on over 3000 individuals, we found that newts can switch migratory tactics over their lifetime. We conclude that migrants and residents coexist through conditional asymmetries, with residents having higher fitness and inferior individuals adopting the migrant tactic. We found that newts are more likely to switch from residency to migrating than the reverse and males were more likely to remain as residents. Migration differences between the sexes are likely driven by reproduction benefits of residency for males and high energetic costs of breeding resulting in lower breeding frequencies for females. Environmental conditions also influence partial migration within a population; we found support for density-dependent processes in the pond strongly influencing the probability of migrating. Our work illustrates how migration can be influenced by a complex range of individual and environmental factors and enhances our understanding of the conditions necessary for the evolution and maintenance of partial migration within populations.
部分迁徙物种中，一部分个体进行迁徙，而另一部分个体则留守原地，这为评估迁徙条件和检验影响迁徙决策的机制提供了机会。我们对两种红斑点蝾螈（Notophthalmus viridescens）种群进行了为期五年的研究，这两种种群由冬季留守繁殖地的个体和迁徙到陆地生境的个体组成。我们使用多状态标记重捕方法来：(1) 检验迁徙者和留守者之间的生存概率是否存在差异；(2) 确定迁徙者是否每年繁殖，或者是否错过繁殖机会；(3) 估计个体转换迁徙策略的频率。我们利用自然种群的生命史参数估计值，并结合之前的实验工作，来评估维持种群部分迁徙的过程，并评估影响迁徙决策的机制。根据对 3000 多个个体的捕获-再捕获信息，我们发现蝾螈可以在其一生中转换迁徙策略。我们的结论是，迁徙者和留守者通过条件不对称性共存，留守者具有更高的适应度，而劣势个体则采取迁徙策略。我们发现，蝾螈从留守到迁徙的转变比相反方向的转变更有可能发生，并且雄性更有可能留守。性别间的迁徙差异可能是由雄性留守的繁殖收益和雌性繁殖频率较低的高能量成本导致的。环境条件也会影响种群内的部分迁徙；我们发现池塘中的密度依赖过程对迁徙概率有强烈影响。我们的工作说明了迁徙如何受到一系列复杂的个体和环境因素的影响，并增强了我们对群体内部分迁徙进化和维持所需条件的理解。
