Tactical departures and strategic arrivals: Divergent effects of climate and weather on caribou spring migrations
Tactical departures and strategic arrivals: Divergent effects of climate and weather on caribou spring migrations
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DOI：
10.1002/ecs2.2971
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发表时间：
2019-12-01
期刊：
影响因子：
2.7
通讯作者：
Boelman, Natalie
中科院分区：
文献类型：
--
作者：
Gurarie, Eliezer;Hebblewhite, Mark;Boelman, Natalie
北极一直在迅速变暖，影响着整个地区的生态过程。驯鹿和驯鹿（Rangifer tarandus）是北极的一个关键物种，在其分布区的许多地方都在减少，但气候和种群之间的确切联系仍然难以捉摸。许多驯鹿种群的显著和戏剧性的大规模迁移，在此期间，几乎所有怀孕的女性在分娩前不久从越冬范围移动到产犊地，可能是气候和驯鹿种群之间的重要联系。然而，移民的驱动力同样神秘。例如，目前尚不清楚驯鹿是否会对即时的物候线索做出反应，是否会对产犊地的条件做出预期，或者是否会受到与身体状况相关的滞后效应的影响。为了调查迁移的驱动因素，我们分析了1995年至2017年来自7个主要鹿群的1000多只驯鹿的运动数据，这些驯鹿横跨阿拉斯加，育空地区，西北地区（NWT）和加拿大的努纳武特，横跨3000公里。我们开发了一个分层模型来估计迁移出发和到达时间，并根据全球气候指数和当地天气状况分析了这些变量，探索了即时和滞后效应，以及融雪时间和植被指数。我们发现了一个大陆范围内的春季迁移出发时间的同步性，主要是由大规模的海洋驱动的气候指数（太平洋十年涛动，北极涛动和北大西洋涛动）。然而，我们也发现，迁移的速度是高度塑性的迁移出发时间较晚，迁移持续时间较短。这种可塑性使得到达时间独立于出发时间及其各自的驱动因素。相反，到达时间在很大程度上取决于前一个夏天的天气条件：凉爽多风的夏天通常会导致第二年提前到达产犊地。我们认为，产妇的身体状况，主要是受限制昆虫骚扰的条件，是一个主要因素，为春季迁移到达时间提前，因此，早期产犊和较高的存活率。我们把这些结果的背景下，气候和驯鹿种群动态之间的机械联系。对迁徙动物进行长期和大规模的观察，可以深入了解远距离集体迁徙动物适应动态和不可预测环境的机制。
The Arctic has been warming rapidly, affecting ecological processes across the region. Caribou and reindeer (Rangifer tarandus) is a keystone Arctic species undergoing declines in many parts of its range, but definitive links between climate and populations remain elusive. The conspicuous and dramatic mass migration of many caribou populations, during which nearly all pregnant females move from wintering ranges to calving grounds shortly before giving birth, may be an important link between climate and caribou populations. The drivers of migration, however, are similarly mysterious. It is unknown, for example, whether caribou respond to immediate phenological cues, anticipate conditions on calving grounds, or are driven by lagged effects related to physical condition. To investigate the drivers of migration, we analyzed movement data from over 1000 individual caribou from seven major herds, spanning 3000 km across Alaska, Yukon, Northwest Territories (NWT), and Nunavut in Canada, from 1995 to 2017. We developed a hierarchical model to estimate migration departure and arrival times, and analyzed these variables against global climate indices and local weather conditions, exploring immediate and lagged effects, as well as snowmelt timing and vegetation indices. We discovered a continent-wide synchrony in spring migration departure times, driven mainly by large-scale, ocean-driven climate indices (Pacific Decadal Oscillation, Arctic Oscillation, and North Atlantic Oscillation). However, we also found that the speed of migration was highly plastic with later migration departure times followed by shorter migration durations. This plasticity made arrival timing independent of departure timing and its respective drivers. Rather, arrival timing depended strongly on weather conditions from the previous summer: cooler and windier summers generally led to earlier arrival at calving grounds the following year. We suggest that maternal body condition, mainly influenced by conditions that limit insect harassment, is a major factor for earlier spring migration arrival timing, and therefore earlier calving and higher survival rates. We place these results in the context of mechanistic links between climate and caribou population dynamics. Long-term and large-scale observations of migratory animals can provide insights into the mechanisms by which long-distance, collective migrants may adapt to dynamic and unpredictable environments.