Partial migration of elk in a heterogeneous landscape

迁徙是自然界最具标志性的过程之一。了解部分迁移（只有一部分人口迁移）的维持，最近引起了种群生态学家的注意，但也引起了自然资源保护主义者的注意，因为面临气候变化和人类足迹不断增加的迁移系统发生了巨大变化。从根本上理解部分迁移的维持需要长期的人口监测，以区分其维持的假设，但对部分迁移的有蹄类动物的长期研究非常罕见。在接下来的5年里，我的研究小组扩展了我们对阿尔伯塔省班夫国家公园附近部分迁徙的麋鹿（Cervus elaphus）种群的13年人口统计研究。我们在过去的研究基础上，比较了移民群体的行为、空间利用和人口统计，解决了三个新问题。首先，最近的理论表明，环境条件的时空变化会强烈影响个体的适应性，而在种群水平上可能会产生相反的影响。我们的问题是，在多大程度上，生境条件的局部空间变化可以抵消影响牧草质量的生长季节（物候）趋势的开始、变化速度和持续时间的随机变化。这是一个在大型食草动物的觅食生态学中没有得到很好研究的领域。其次，我们将重点扩展到狼对捕食者群落自上而下的影响，并探讨了大型食肉动物相互作用如何影响麋鹿在3个时期（产犊期、夏末和冬季）捕食风险的时空格局，这些时期对食草动物的运动和营养限制不同。第三，来自哺乳动物研究的少量数据表明，在迁徙策略之间的转换是罕见的，这表明它们是固定的。这个系统中麋鹿的遗传数据不支持这一点，经过13年的转换，现在平均每年16%(3-25%)，这意味着比我们最初认为的更大的作用。我们现在假设部分迁移是通过密度相关的适应性平衡和切换来维持的。为了评估这一假设，我们首先需要确定是内在因素（年龄、学习）还是外在因素（捕食风险、饲料质量）影响转换。我们计划建立空间和空间人口模型来评估部分迁移背后的机制，并说明这些方法如何有助于制定环境变化下保护迁移人口的地方管理和全球战略。

Migration is one of nature's most iconic processes. Understanding the maintenance of partial migration, where only a portion of the population migrates, has caught the recent attention of population ecologists, but also conservationists because of the dramatic changes in migratory systems facing climate change and a growing human foot print. Understanding the maintenance of partial migration fundamentally requires long-term demographic monitoring to distinguish among hypotheses for its maintenance, but long-term studies on partially migratory ungulates are exceedingly rare. In the next 5 years, my research team extends our 13-year demographic study of a partially migratory elk (Cervus elaphus) population near Banff National Park, Alberta. We build on our past research comparing behavior, space use, and demography among migratory segments addressing 3 new questions. First, recent theory indicates spatial and temporal variation in environmental conditions strongly affects individual fitness in ways that may have opposing effects at the population level. We ask to what extent can local spatial variation in habitat conditions off-set stochastic variation in the onset, rate of change, and duration of growing season (phenological) trends that drive forage quality at the large-scale. This is an area not well studied in the foraging ecology of large herbivores. Second, we expand our focus on the top-down effects from wolves to predator communities and ask how large carnivore interactions influence the spatiotemporal patterns in predation risk for elk during 3 periods (calving, late summer and winter) that impose different movement and nutritional constraints on herbivores. Third, scant data from studies on mammals indicate switching among migratory strategies is rare, pointing to them being fixed. Genetic data from elk in this system do not support this, and after 13 years switching now averages 16% (3-25%) per year, implicating a bigger role than we originally argued. We now hypothesize that partial migration is maintained by density-dependent fitness balancing and switching. To evaluate this hypothesis we first need to determine whether intrinsic (age, learning) or extrinsic factors (predation risk, forage quality) influence switching. We plan to build spatial and aspatial demographic models to evaluate the mechanisms behind partial migration and illustrate how these approaches can help devise local management and global strategies for conserving migratory populations under environmental change.