RAPID: Sudden reproductive failure in a declining caribou population - investigation of links to warming-related vegetation changes

驯鹿和驯鹿是北极地区最常见的陆地动物之一，但随着过去30年北极变暖，几乎所有驯鹿的数量都在下降。虽然还没有确定它们减少的单一原因，但有一种说法是，变暖导致了更多更大的灌木的生长，这些灌木对驯鹿的营养价值低于它们喜欢的植物，如草和杂类草（较小的开花植物）。自2002年以来，我们一直在研究格陵兰岛Kangerlussuaq附近的驯鹿，在此期间，该地区的驯鹿数量稳步下降。此外，2022年，他们在过去20年中首次在该地区没有生产小牛。我们将在2023年夏天重新访问该地区，调查那里的驯鹿数量，评估小牛产量，并收集灌木，草和杂类草以分析其营养成分。这些驯鹿食物质量的措施将与2005年在该地区采取的类似措施进行比较，当时天气凉爽，驯鹿更丰富，灌木更小，更不常见。这将有助于确定气候变暖是否降低了康克鲁斯瓦格附近驯鹿的食物质量，以及这是否导致了它们的下降。驯鹿对Kangerlussuaq地区的狩猎和旅游业很重要，该项目的成果将与格陵兰自然资源研究所分享，该研究所负责监督格陵兰驯鹿的监测和管理。研究结果还有助于了解影响北极其他地区驯鹿和驯鹿数量减少的因素，这些地区的驯鹿和驯鹿对传统生计很重要。在整个北极地区，驯鹿和野生驯鹿（Rangifer tarandus）数量正在减少，在过去30年里，这两个物种的总数量减少了50%以上。与此同时，北极的变暖速度是全球平均水平的2- 3倍。虽然没有单一的因素可能解释该物种的下降，但一些证据将其与变暖相关的北极苔原灌木的主导地位增加联系起来，这些灌木对驯鹿和野生驯鹿来说不如他们喜欢的草和杂类草那么美味。在格陵兰岛的Kangerlussuaq附近，我们从2002年开始对驯鹿进行的年度调查显示，自2005年以来，驯鹿的数量下降了80%，繁殖完全失败（即，2022年夏季首次出现。我们推测，这种下降和繁殖失败可能与增加灌木丰富的网站与夏季变暖。我们将于2023年夏季返回现场，通过调查总丰度和产犊量来评估驯鹿的状况，并通过对灌木、草、莎草和杂类草的碳和氮含量进行采样和分析来评估植被的营养状况。这将有助于通过与2005年夏季在该地点收集的类似数据进行比较来检验我们的假设，当时驯鹿更丰富，小牛产量接近最大，灌木更小，更少，仲夏平均温度接近1 ℃。驯鹿和野生驯鹿对整个北极地区的传统生计和文化完整性非常重要，它们的减少与一些当地社区的传统知识转让、情感健康和社会凝聚力的下降有关。此外，Kangerlussuaq地区的驯鹿对生存和狩猎很重要，对当地的非消费性旅游经济也至关重要。该项目产生的数据和结果将与格陵兰自然资源研究所分享，该研究所负责监督格陵兰全境驯鹿的监测和管理。此外，将努力利用该项目的成果，通过加州大学戴维斯分校的教育和外联活动，提高公众对北极驯鹿和野生驯鹿数量下降的认识。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Caribou and the closely-related reindeer are among the most common land animals in the Arctic, yet almost every population of them has been declining as the Arctic has warmed over the past 30 years. While no single cause of their decline has been identified, one suggestion is that warming has resulted in the growth of more, larger shrubs that are less nutritious for caribou than plants they prefer such as grasses and forbs (smaller flowering plants). We have been studying caribou near Kangerlussuaq, Greenland since 2002, and in that time their numbers in the area have dropped steadily. Moreover, in 2022 they produced no calves in the area for the first time in the past 20 years. We will revisit the area in the summer of 2023 to survey the number of caribou there, assess calf production, and collect shrubs, grasses, and forbs for analysis of their nutritive content. These measures of caribou food quality will be compared to similar measures taken in the area in 2005 when it was cooler, caribou were more abundant, and shrubs were smaller and less common. This will help determine whether warming has reduced food quality for caribou near Kangerlussuaq, and whether this has contributed to their decline. Caribou are important for hunting and tourism in the Kangerlussuaq area and results of this project will be shared with the Greenland Institute of Natural Resources who oversees monitoring and management of caribou in Greenland. Results might also contribute to understanding of factors influencing declines of caribou and reindeer in other parts of the Arctic where they are important to traditional livelihoods.Across the Arctic, caribou and wild reindeer (both Rangifer tarandus) are in decline, with more than 50% of the species’ total abundance having been lost over the past 30 years. Simultaneously, the Arctic has warmed at a rate 2-3x the global average. While no single factor likely explains the species’ decline, some evidence links it to a warming-related increasing dominance of arctic tundra by shrubs that are less palatable to caribou and wild reindeer than the grasses and forbs they prefer. Near Kangerlussuaq, Greenland our annual surveys of caribou that began in 2002 have revealed an 80% decline in their numbers since 2005 and a complete reproductive failure (i.e., a lack of calves) for the first time in summer 2022. We hypothesize that this decline and reproductive failure might relate to an increase in shrub abundance at the site coincident with summer warming. We will return to the site in summer 2023 to assess the status of caribou there through surveys of total abundance and calf production, and to assess the nutritive status of vegetation through sampling and analysis of carbon and nitrogen content of shrubs, grasses and sedges, and forbs. This will facilitate a test of our hypothesis through comparison to similar data collected at the site in summer 2005, when caribou were more abundant, calf production was near maximal, shrubs were smaller and less abundant, and mid-summer mean temperature was nearly 1oC cooler. Caribou and wild reindeer are important to traditional livelihoods and cultural integrity throughout the Arctic, and their decline has been associated with declines in traditional knowledge transfer, emotional well-being, and social cohesion in some local communities. Additionally, caribou in the Kangerlussuaq area are important to subsistence- and trophy hunting as well as being vital to the local non-consumptive tourism economy. Data and results deriving from this project will be shared with the Greenland Institute of Natural Resources, which oversees monitoring and management of caribou throughout Greenland. Moreover, efforts will be made to use results of this project to raise public awareness of the decline of caribou and wild reindeer across the Arctic through educational and outreach events at UC Davis.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.