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

驯鹿和与驯鹿关系密切的驯鹿是北极最常见的陆地动物之一，但随着北极在过去30年里变暖，它们的几乎每一个种群都在下降。虽然还没有确定它们减少的单一原因，但有一种说法是，气候变暖导致了更多、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，如草和杂草(开花较小的植物)。自2002年以来，我们一直在格陵兰岛康鲁斯苏阿克附近研究驯鹿，在此期间，它们在该地区的数量一直在稳步下降。此外，2022年，他们在过去20年来首次没有在该地区生产小牛。我们将在2023年夏天再次访问该地区，调查那里的驯鹿数量，评估牛犊产量，并收集灌木、草和杂草来分析它们的营养含量。这些衡量驯鹿食物质量的指标将与2005年该地区采取的类似措施进行比较，当时天气更凉爽，驯鹿数量更多，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格卢斯苏阿克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地区的狩猎和旅游很重要，该项目的成果将与负责监测和管理格陵兰驯鹿的格陵兰自然资源研究所分享。研究结果也可能有助于理解影响北极其他地区驯鹿和驯鹿数量减少的因素，因为它们对传统生计很重要。在整个北极，驯鹿和野生驯鹿(均为Rangifer tarandus)正在减少，在过去30年中，该物种总丰度的50%以上已经丧失。与此同时，北极变暖的速度是全球平均水平的2-3倍。虽然没有单一因素可能解释该物种的衰落，但一些证据表明，与气候变暖相关的北极苔原日益占据主导地位的是灌木，这些灌木对驯鹿和野生驯鹿的吸引力低于它们喜欢的草和杂草。我们从2002年开始对格陵兰岛坎格卢斯苏亚克附近的驯鹿进行年度调查，结果显示，自2005年以来，驯鹿的数量下降了80%，2022年夏天首次出现了完全的生殖障碍(即缺少小鹿)。我们推测，这种下降和繁殖失败可能与该地点灌木丰度的增加与夏季变暖相一致。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那里的驯鹿状况，并通过采样和分析灌木、草、莎草和杂草的碳和氮含量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，当时驯鹿更多，小牛产量接近最高，灌木更小，数量更少，仲夏平均温度几乎低1摄氏度。驯鹿和野生驯鹿对整个北极的传统生计和文化完整性很重要，它们的衰落与一些当地社区的传统知识转让、情感福祉和社会凝聚力的下降有关。此外，Kangerlussuaq地区的驯鹿对于生存和战利品狩猎非常重要，对当地非消费性旅游经济也是至关重要的。该项目的数据和结果将与格陵兰自然资源研究所分享，该研究所负责监督整个格陵兰的驯鹿监测和管理。此外，加州大学戴维斯分校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展活动，提高公众对整个北极驯鹿和野生驯鹿数量减少的认识。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.