Department of Biology, Queen's University, Kingston, Ontario, K7L 3N6, Canada.
School of Biological Sciences, Monash University, Clayton, Victoria, 3800, Australia.
Ecol Appl. 2017 Oct;27(7):2061-2073. doi: 10.1002/eap.1590. Epub 2017 Aug 29.
Global declines in caribou and reindeer (Rangifer) populations have drawn attention to the myriad of stressors that these Arctic and boreal forest herbivores currently face. Arctic warming has resulted in increased tundra shrub growth and therefore Rangifer forage quantity. However, its effects on forage quality have not yet been addressed although they may be critical to Rangifer body condition and fecundity. We investigated the impact of 8 yrs of summer warming on the quality of forage available to the Bathurst caribou herd using experimental greenhouses (n = 5) located in mesic birch hummock tundra in the central Canadian Low Arctic. Leaf forage quality and digestibility characteristics associated with nutrients (nitrogen and phosphorus), phenolics, and fiber were measured on the deciduous shrub Betula glandulosa (an important Rangifer diet component) at six time points through the growing season, and on five other very common vascular plant and lichen species in late summer. Experimental warming reduced B. glandulosa leaf nitrogen concentrations by ~10% in both late June and mid-July, but not afterwards. It also reduced late summer forage quality of the graminoid Eriophorum vaginatum by increasing phenolic concentrations 38%. Warming had mixed effects on forage quality of the lichen Cetraria cucullata in that it increased nutrient concentrations and tended to decrease fiber contents, but it also increased phenolics. Altogether, these warming-induced changes in forage quality over the growing season, and response differences among species, highlight the importance of Rangifer adaptability in diet selection. Furthermore, the early season reduction in B. glandulosa nitrogen content is a particular concern given the importance of this time for calf growth. Overall, our demonstration of the potential for significant warming impacts on forage quality at critical times for these animals underscores the importance of effective Rangifer range conservation to ensure sufficient appropriate habitat to support adaptability in forage selection in a rapidly changing environment.
全球驯鹿（Rangifer）和北美驯鹿种群数量的下降引起了人们对这些北极和北方森林食草动物目前面临的多种压力源的关注。北极变暖导致苔原灌木生长增加，从而增加了驯鹿的饲料数量。然而，其对饲料质量的影响尚未得到解决，尽管它们可能对驯鹿的身体状况和繁殖力至关重要。我们通过在加拿大中北极的湿润桦木丘状冻原中设置的 5 个实验温室（n=5），研究了 8 年夏季变暖对巴瑟斯特驯鹿群可用饲料质量的影响。在整个生长季节的 6 个时间点，我们对落叶灌木细叶杜香（Betula glandulosa）（一种重要的驯鹿饮食成分）的饲料质量和与营养物质（氮和磷）、酚类化合物和纤维相关的消化特性进行了测量，并且在夏末对其他 5 种非常常见的维管植物和地衣物种进行了测量。实验性增温使细叶杜香叶片中的氮浓度在 6 月底和 7 月中旬分别降低了约 10%，但之后没有降低。它还通过增加 38%的酚类化合物浓度，降低了夏末禾本科植物毛果苔草的饲料质量。变暖对地衣 C. cucullata 的饲料质量有混合影响，因为它增加了营养物质浓度，并且往往降低了纤维含量，但也增加了酚类化合物。总之，这些在生长季节中引起的饲料质量变化以及物种之间的反应差异，突出了驯鹿在饮食选择方面的适应性的重要性。此外，考虑到这段时间对小牛生长的重要性，细叶杜香氮含量的早期减少尤其令人担忧。总体而言，我们证明了在这些动物关键时期，饲料质量可能会受到显著变暖的影响，这突显了有效保护驯鹿栖息地的重要性，以确保有足够的适宜栖息地来支持在快速变化的环境中对饲料选择的适应性。
