Department of Environmental and Forest Biology, College of Environmental Science and Forestry, State University of New York, Syracuse, New York, 13210, USA.
Roosevelt Wild Life Station, College of Environmental Science and Forestry, State University of New York, Syracuse, New York, 13210, USA.
Ecology. 2019 Jun;100(6):e02658. doi: 10.1002/ecy.2658. Epub 2019 Apr 18.
To understand how migratory behavior evolved and to predict how migratory species will respond to global environmental change it is important to quantify the fitness consequences of intra- and inter-individual variation in migratory behavior. Intra-individual variation includes behavioral responses to changing environmental conditions and hence behavioral plasticity in the context of novel or variable conditions. Inter-individual variation determines the degree of variation on which selection can act and the rate of evolutionary responses to changes in average and extreme environmental conditions. Here we focus on variation in the partial migratory behavior of giant Galápagos tortoises (Chelonoidis spp.) and its energetic consequences. We evaluate the extent and mechanisms by which tortoises adjust migration timing in response to varying annual environmental conditions, and integrate movement data within a bioenergetic model of tortoise migration to quantify the fitness consequences of migration timing. We find strong inter-individual variation in the timing of migration, which was not affected by environmental conditions prevailing at the time of migration but rather by average expectations estimated from multi-annual averaged conditions. This variation is associated with an average annual loss in efficiency of ~15% relative to optimal timing based on year-specific conditions. These results point towards a limited ability of tortoises to adjust the timing of their migrations based on prevailing (and, by extension, future) conditions, suggesting that the adaptability of tortoise migratory behavior to changing conditions is predicated more by past "normal" conditions than responses to prevailing, changing conditions. Our work offers insights into the level of environmental-tuning in migratory behavior and a general framework for future research across taxa.
为了理解迁徙行为是如何进化的，并预测迁徙物种将如何应对全球环境变化，量化迁徙行为个体内和个体间变异对适应度的影响非常重要。个体内变异包括对不断变化的环境条件的行为反应，因此在新的或变化的条件下具有行为可塑性。个体间变异决定了选择可以作用的变异程度，以及对平均和极端环境条件变化的进化反应速度。在这里，我们关注加拉帕戈斯巨龟（Chelonoidis spp.）部分迁徙行为的变异及其对能量的影响。我们评估了龟类在响应不同年度环境条件下调整迁徙时间的程度和机制，并将移动数据整合到龟类迁徙的生物能量模型中，以量化迁徙时间对适应度的影响。我们发现，迁徙时间存在强烈的个体间变异，这种变异不受迁徙时的环境条件影响，而是受多年平均条件下的平均预期影响。这种变异与基于特定年份条件的最佳时间相比，平均每年效率损失约为 15%。这些结果表明，龟类调整迁徙时间的能力有限，无法根据当前（以及未来）的条件，这表明龟类迁徙行为对变化条件的适应性更多地取决于过去的“正常”条件，而不是对当前变化条件的反应。我们的工作为了解迁徙行为的环境适应水平提供了线索，并为未来跨分类群的研究提供了一般框架。
