Post-Graduate Program in Wildlife Biology and Conservation, National Centre for Biological Sciences, Bangalore, India.
Oecologia. 2010 Feb;162(2):453-62. doi: 10.1007/s00442-009-1467-x. Epub 2009 Sep 27.
Many mammalian herbivores show a temporal diet variation between graminoid-dominated and browse-dominated diets. We determined the causes of such a diet shift and its implications for conservation of a medium-sized ungulate-the bharal Pseudois nayaur. Past studies show that the bharal diet is dominated by graminoids (>80%) during summer, but the contribution of graminoids declines to about 50% in winter. We tested the predictions generated by two alternative hypotheses explaining the decline: low graminoid availability during winter causes bharal to include browse in their diet; bharal include browse, with relatively higher nutritional quality, in their diet to compensate for the poor quality of graminoids during winter. We measured winter graminoid availability in areas with no livestock grazing, areas with relatively moderate livestock grazing, and those with intense livestock grazing pressures. The chemical composition of plants contributing to the bharal diet was analysed. The bharal diet was quantified through signs of feeding on vegetation at feeding locations. Population structures of bharal populations were recorded using a total count method. Graminoid availability was highest in areas without livestock grazing, followed by areas with moderate and intense livestock grazing. The bharal diet was dominated by graminoids (73%) in areas with highest graminoid availability. Graminoid contribution to the bharal diet declined monotonically (50, 36%) with a decline in graminoid availability. Bharal young to female ratio was 3 times higher in areas with high graminoid availability than areas with low graminoid availability. The composition of the bharal winter diet was governed predominantly by the availability of graminoids in the rangelands. Our results suggest that bharal include more browse in their diet during winter due to competition from livestock for graminoids. Since livestock grazing reduces graminoid availability, creation of livestock-free areas is necessary for the conservation of grazing species such as the bharal and its predators including the endangered snow leopard in the Trans-Himalaya.
许多哺乳动物食草动物在以禾本科植物为主的饮食和以灌木为主的饮食之间表现出时间上的饮食变化。我们确定了这种饮食转变的原因及其对中型有蹄类动物——扭角羚保护的影响。过去的研究表明，扭角羚的饮食在夏季以禾本科植物为主（>80%），但在冬季，禾本科植物的比例下降到约 50%。我们测试了两种解释这种下降的替代假设所产生的预测：冬季禾本科植物供应不足导致扭角羚将灌木纳入其饮食；扭角羚在饮食中加入相对营养质量较高的灌木，以弥补冬季禾本科植物质量较差的问题。我们测量了没有放牧、中度放牧和高强度放牧压力的地区冬季禾本科植物的可利用性。分析了对扭角羚饮食有贡献的植物的化学成分。通过在觅食地点的植物采食痕迹来量化扭角羚的饮食。使用总数法记录扭角羚种群的种群结构。在没有放牧的地区，禾本科植物的可利用性最高，其次是中度和高强度放牧的地区。在禾本科植物可利用性最高的地区，扭角羚的饮食主要以禾本科植物为主（73%）。随着禾本科植物可利用性的下降，扭角羚饮食中禾本科植物的比例呈单调下降（50%、36%）。在禾本科植物可利用性高的地区，扭角羚幼仔与雌性的比例是禾本科植物可利用性低的地区的 3 倍。扭角羚冬季饮食的组成主要由牧场中禾本科植物的可利用性决定。我们的研究结果表明，由于与牲畜竞争禾本科植物，扭角羚在冬季会在饮食中加入更多的灌木。由于牲畜放牧会降低禾本科植物的可利用性，因此在喜马拉雅山地区，为了保护放牧物种（如扭角羚及其包括濒危雪豹在内的捕食者），需要创建无放牧区。
