贺兰山牦牛冬春季的生境选择

在2009年12月－2010年1月和2010年4－5月，采用样线法结合直接观察法对贺兰山牦牛的冬春季生境选择进行了研究。结果表明，牦牛冬季对11种生境因子有选择性，偏爱山地针叶林带，海拔小于2 000 m，优势乔木为灰榆，坡度小于10，下坡位，距水源距离大于1 200 m，人为干扰距离2 000－4 000 m，隐蔽级大于70 %；春季牦牛对13种利用生境生态因子有选择性，偏爱于亚高山灌丛和草甸带，海拔大于3 000 m，乔木密度小于1株，乔木高度小于3 m，乔木距离大于3 m，灌木密度大于4 0株，灌木距离小于1 m，植被盖度大于7 0 %，上坡位，距水源的距离小于8 00 m，人为干扰距离大于4 000 m，隐蔽级大于7 0 %。冬春季牦牛在海拔、植被类型、地形特征、优势乔木、灌木种类、坡位、坡向、人为干扰距离、距水源距离上存在显著差异。主成分分析表明冬季第一主成分的贡献率21.100 %，其中绝对值较大的相关系数是乔木距离、优势乔木、乔木高度和乔木密度；春季第一主成分的贡献率是31.247 %，其中绝对值较大的相关系数是植被类型、海拔高度、地形特征和灌木密度。与其他分布地区的牦牛相比，贺兰山地区的牦牛能适应当地的地理特征和气候环境。

Habitat selection of feral yak in winter and spring in the Helan Mountains, China

The yak (Bos grunniens), sometimes called "the boat of the plateau", is an endemic species of the Qinghai-Tibet Plateau, famous for its resistance to cold and importance as a form of transport. The total number of adults may be close to 10,000 because the total population was estimated to be around 15,000 in 1995. Nevertheless, the species was listed as "Vulnerable" in the World Conservation Union's Red List of Threatened Animals because it is inferred that it has declined by over 30% over the last 30 years. Poaching, including commercial poaching for meat, has been the most serious threat to wild yaks. The species was listed on CITES Appendix I. Wild yaks have been protected in China since 1962, and are currently listed as a Class I protected animal, which means that they are fully protected by government law. In China, wild yaks are found in a number of large nature reserves, including the Arjin Shan, Chang Tang, Kekexili, Sanjiangyuan, and Yanchiwan Nature Reserves, although none of these reserves provide complete protection from habitat loss or occasional poaching. The yak population in the Helan Mountains is a reintroduced population from Qinghai-Tibet Plateau, and is only distributed in the Halawu Valleys and the surrounding areas, in the Helan Mountain Reserve in Inner Mongolia. Because their habitat selection had not been previously studied, we conducted surveys from December 2009 to January 2010 and from April to May 2010 to study yak habitat selection in winter and spring. Twenty line transects were established along seven valleys. We identified a total number of 103 used plots in winter and 129 in spring. To provide comparison plots for the analysis of habitat selections, we surveyed 188 randomly placed plots in winter and 207 randomly placed plots in spring by systematically placing transects in areas with no obvious evidence of yak use. Data on 18 topographic and biological variables were collected in each plot. In winter, yaks preferred montane coniferous forest, lower altitude (<2000 m), habitat dominated by Ulmus glaucescens, more gentle slopes (<10°), sites closer to the foot of the mountain, areas distant from water resource (>1200 m), moderate distance from human disturbance (2000-4000 m) and abundant hiding cover (>70%). In spring, yak preferred subalpine shrubland and meadow, higher altitude (>3000 m), lower tree density (<1 tree/100 m²), lower tree height (<3 m), greater distances from trees (>3 m), higher shrub density (>40 trees/100 m²), short distance to shrub (<1 m) and higher vegetation coverage (>70%). Habitat selection of the yak showed significant differences in vegetation type, landform feature, dominant tree species, shrub type, position on mountain (e.g. top or base), slope direction, distance from human disturbance and distance from water resource between winter and spring. Results of principal components analysis indicated that the first principal component axis accounted for 21.10% of the total variance in habitat use during winter, with the highest correlation coefficient for distance to nearest tree, dominant tree species, tree height, tree density. In spring, the first principal components axis accounted for 31.247% of the variance, with highest correlation coefficient for vegetation type, altitude, landform feature, shrub density. Compared to other migrating yak populations distributed in Qinghai-Tibet Plateau, there were significant differences in yak habitat selection between different seasons in the Helan Mountains. Yaks are acclimatized to the particular geography and climate in the Helan Mountains.