内蒙古达乌尔鼠兔越冬群体大小与捕食风险的研究

Study on Predation Risk and Group Size of Daurian Pika in Inner Mongolia

达乌尔鼠兔(Ochotona dauurica)是内蒙古草原的主要鼠种之一,分布在草地和榆树(Ulmus pumila)疏林下,在冬季会形成数量不同的越冬集群。达乌尔鼠兔在秋季和冬季常常会受到艾虎(Mustela eversmanii)的攻击。为研究达乌尔鼠兔越冬集群大小与来自艾虎的捕食风险的关系,2004年10月上旬在内蒙古锡林郭勒盟锡林浩特市白音锡勒牧场的五连榆树疏林地,以洞口计数法调查分布于林下的达乌尔鼠兔种群,采用洞口数量多少作为鼠兔秋季集群大小的指标。清除实验区达乌尔鼠兔洞群范围内的所有鼬科动物粪便。1个月之后,分别统计洞群留有艾虎粪便和洞群被艾虎挖掘过的达乌尔鼠兔家族数量,分析了艾虎对不同大小集群的达乌尔鼠兔家群的捕食选择偏好。统计结果显示,艾虎在集群大的达乌尔鼠兔家群周围更容易留下粪便(P<0.05),并且更倾向挖掘集群大的达乌尔鼠兔家群(P<0.05)。这表明达乌尔鼠兔越冬家群成员数量越多,其来自艾虎的捕食风险就越大。从本次实验结果来看,越冬期间天敌选择性的捕食风险的存在抑制了达乌尔鼠兔越冬集群的增长,从而使其越冬家族数量维持在限定的规模和水平。

Group size of overwintering colonies of Daurian Pika(Ochotona dauurica)may affect predation risk by mammals.Daurian Pika is one of the main rodent species in the grasslands of Inner Mongolia,which distributed under grasslands and Elm(Ulmus pumila)sparse forests,and will form different numbers of overwintering colonies in winter.Steppe Polecat(Mustela evermanni)is one of the main predators of Dauurian Pika and often attacks the Daurian Pika’s burrow in autumn and winter.To investigate whether the size of the Dauurian Pika’s colony is affected by the risk of predation from Steppe Polecat.We conducted related experiments in the Baiyinxile pasture,Xilinhot City,Xilinguole League,Inner Mongolia,from October to November,2004.The number of Daurian Pika burrows was used to estimate group size of pika.The number fecal droppings and holes excavated by Steppe Polecat within the habitat of each Daurian Pika colony were recorded as indicators of predation pressure.The nonparametric Mann-Whitney U test was used to detect differences in social group size between the colonies with and without signs of Polecat activity.The result showed that the rank sum of the colonies not surrounded by Polecat feces was 2700.5,whereas colonies surrounded by Polecat feces was 1040.5(U=422.5,Adjusted Z Value=-2.247,Adjusted P<0.05).The rank sum of colonies with holes dug by Polecat was 461,whereas the rank sum of colonies without the Polecat excavation was 3280(U=120,Adjusted Z Value=-2.493,Adjusted P<0.05)(Table 1).The result of Mann-Whitney test suggested significant differences in predator preference between the two groups of colonies.In addition,the frequencies of feces and excavation trails rise with the increase of group size(Fig.1 and 2).This difference indicated that the Steppe Polecat significantly preference Daurian Pika colonies with high group size.From the results of this experiment,the existence of the selective predation risk of the Steppe Polecat inhibited the increase of the overwintering clusters of the Dauurian Pikas during the wintering period,thereby maintaining the number of overwintering colonies at a limited scale and level.