内蒙古草原布氏田鼠与绵羊的营养生态位研究

放牧活动对小型啮齿动物种群数量的影响是草原生态系统研究中的热点问题，确定绵羊和小型啮齿动物的营养生态位关系对于草原生态系统的管理具有重要的作用。运用粪便显微分析法分析了内蒙古草原动物生态研究站大型野外围栏内布氏田鼠和绵羊在6-9月份的食谱组成，确定两种草食动物食性选择和营养生态位的变化，从食物利用途径揭示放牧活动对布氏田鼠种群数量的影响方式及二者之间的竞争与共存关系。研究结果表明：围栏中共有23种植物，其中糙隐子草、克氏针茅、羊草和刺藜是围栏中的优势植物；布氏田鼠共取食10种植物，绵羊共取食8种植物，禾本植物为两种动物的主要采食植物。布氏田鼠和绵羊的喜食植物种类都存在季节性变化；除7月外，两种动物的食物多样性与围栏植物多样性有显著的正相关关系，表明动物的食性选择受植物资源变化的影响。布氏田鼠和绵羊具有很高的营养生态位重叠度，除8月（0.691）外，6、7、9月份的营养生态位重叠度均高于0.9，表明二者之间存在激烈的食物竞争；放牧活动极显著地降低了禾本科植物的地上生物量，导致布氏田鼠的食物数量减少；放牧处理下布氏田鼠的喜食植物的物种数和营养生态位宽度（除9月）增加，导致布氏田鼠的食物质量下降。以上研究结果说明，较高的营养生态位重叠度引起动物间激烈的食物竞争；放牧会影响围栏中植物资源的变化，进而影响布氏田鼠的食性选择，放牧活动可能通过降低布氏田鼠的食物数量和质量对其种群数量产生负面效应；这也说明适度的放牧活动在增加人类对草场利用的同时，又可降低小型啮齿动物的数量及危害。

Trophic niches of Brandt's vole (Lasiopodomys brandtii) and sheep (Ovis aries) in the Inner Mongolia Grassland

The influence of grazing activities on the population of small rodents is a hot issue in grassland ecosystem research. The determination of trophic niche relationship between sheep and small rodents plays an important role on the management of grassland ecosystems. In present study, microscopic analysis of feces was applied to analyze the diet composition of Brandt''s voles and sheep, whose fecal samples were collected from the Animal Ecology Research Station located in the Maodeng pasture (Xilinhot, Inner Mongolia, China) from June to September, 2012. The changes in diet selection and trophic niches of the two herbivores would be determined to reveal the patterns by which the population of Brandt''s vole was affected by grazing activities, and the relationship of competition and coexistence between these two herbivores from the perspective of food utilization. Our results showed that a total of 23 plant species were found in the fence, with Cleistogenes squarrosa, Stipa krylovii, Leymus chinensis, and Dysphania aristata being the dominant plants. Brandt''s vole and sheep fed on 10 and 8 plant species, respectively. Gramineous plants were the main forage plants for both animals. Brandt''s vole and sheep had their favorite plant species which varied in different seasons; except for that in July, there was a significantly positive correlation between dietary diversity of animals and plant diversity within the fences, suggesting an effect of changes in available plant resources on animals'' diet selections. The trophic niche overlap between Brandt''s vole and sheep was higher than 0.9 except for that in August (0.691), indicating that there was fierce food competition between the two. In addition, the grazing activities significantly reduced the aboveground biomass of plants from the Gramineae family, leading to a decrease in the quantity of food for Brandt''s vole; and grazing activities significantly increased the number of plant species favored by Brandt''s voles and the breadth of its trophic niche (except for September), leading to a decrease in the quality of food for Brandt''s vole. These results indicated that high trophic niche overlap could cause fierce food competition between animals; grazing could affect the diet selection of Brandt''s voles by influencing changes of plant resources in the fences, and grazing activities may have a negative effect on the population of Brandt''s vole through reducing the quality and quantity of its food. These findings suggest that moderate grazing activities not only increase the utilization of pastures but also reduce the population of small rodents and their damage.