Christie Katie S, Ruess R W
The Institute of Arctic Biology, University of Alaska Fairbanks, 902 N. Koyukuk Dr., Fairbanks, AK, USA,
Oecologia. 2015 Jul;178(3):773-81. doi: 10.1007/s00442-015-3265-y. Epub 2015 Feb 20.
In some ecosystems, vertebrate herbivores increase the nutritional quality and biomass of their food source through repeated grazing, thereby manipulating their environment to support higher densities of animals. We tested whether ptarmigan (Lagopus lagopus and L. muta) are capable of regulating the nutritional quality, abundance, and availability of feltleaf willow (Salix alaxensis) buds using a simulated browsing experiment and a feeding preference study with wild birds. Simulated ptarmigan browsing resulted in smaller buds, but greater numbers of buds per shoot. Furthermore, browsing altered the morphology of willow branches such that buds were at higher densities and closer to snow level compared to unbrowsed controls. Browsing increased the number of willows with accessible buds (buds within 50 cm of snow level) from 55 to 89%, and increased total accessible bud biomass from 113 ± 30 to 129 ± 50 mg/ramet. Browsing did not affect bud nitrogen or carbon concentration and slightly reduced protein precipitation capacity (tannins) in buds the following winter, indicating that ptarmigan browsing does not induce a defensive response in this species. When branches of broomed (previously browsed) and unbroomed willows were placed in the snow at equal heights, ptarmigan showed no preference for either type; however, they obtained more buds from broomed willows. Increased accessibility and density of willow buds caused by browsing has the potential to increase habitat carrying capacity, thereby supporting higher densities of ptarmigan.
在一些生态系统中，脊椎动物食草动物通过反复啃食来提高其食物来源的营养质量和生物量，从而改变它们的环境以支持更高密度的动物生存。我们通过一项模拟啃食实验以及一项针对野生鸟类的取食偏好研究，来测试雷鸟（柳雷鸟和岩雷鸟）是否能够调节毡毛柳（阿拉斯加柳）芽的营养质量、数量和可获取性。模拟雷鸟啃食导致芽变小，但每枝上的芽数量增多。此外，啃食改变了柳树树枝的形态，与未被啃食的对照相比，芽的密度更高且更接近雪面。啃食使有可获取芽（雪面以下50厘米范围内的芽）的柳树数量从55%增加到89%，并使可获取芽的总生物量从113±30毫克/分株增加到129±50毫克/分株。啃食并未影响芽中的氮或碳浓度，且在次年冬季略微降低了芽中的蛋白质沉淀能力（单宁），这表明雷鸟啃食并未在该物种中引发防御反应。当将经过啃食（之前被啃食过）和未经过啃食的柳树树枝以相同高度放置在雪中时，雷鸟对这两种类型均无偏好；然而，它们从经过啃食的柳树上获取了更多的芽。啃食导致柳树芽的可获取性和密度增加，这有可能提高栖息地的承载能力，从而支持更高密度的雷鸟生存。
