Partial migration of elk in a heterogeneous landscape

迁徙是自然界最具标志性的过程之一。由于面临气候变化的迁徙系统的戏剧性变化和越来越多的人类足迹，对维持部分迁徙的理解最近引起了人口生态学家和自然资源保护者的注意。理解部分迁徙的维持从根本上需要长期的人口监测，以区分维持部分迁徙的假设，但对部分迁徙有蹄类的长期研究极其罕见。在接下来的5年里，我的研究团队延长了我们对艾伯塔省班夫国家公园附近部分迁徙的麋鹿(Cervus Elaffus)种群进行了13年的人口统计学研究。我们在过去研究的基础上，比较了迁徙人群的行为、空间使用和人口统计学，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强烈地影响着个体的适合度，而这种影响可能会在种群水平上产生相反的影响。我们问，生境条件的局部空间变化在多大程度上可以抵消生长季节(物候)趋势的开始、变化速度和持续时间的随机变化，这些趋势在大范围内推动牧草质量。在大型食草动物的觅食生态学中，这是一个研究较少的地区。其次，我们将重点从狼的自上而下效应扩展到捕食者群落，并研究了在对食草动物施加不同运动和营养限制的三个时期(产犊、夏末和冬季)，大型食肉动物的相互作用如何影响麋鹿捕食风险的时空模式。第三，对哺乳动物的研究几乎没有数据表明在迁徙策略之间进行切换的情况很少，这表明它们是固定的。在这个系统中，麋鹿的基因数据不支持这一点，13年后，现在平均每年转换16%(3-25%)，这意味着一个比我们最初争论的更大的角色。我们现在假设，部分迁移是通过密度相关的适应度平衡和切换来维持的。为了评估这一假设，我们首先需要确定内在因素(年龄、学习)或外在因素(捕食风险、饲料质量)是否影响转换。我们计划建立空间和空间人口模型，以评估部分移民背后的机制，并说明这些方法如何帮助制定在环境变化下保护迁徙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.