内蒙古典型草原区狭颅田鼠集群数量与被捕食风险的关系

2005年9月15日—30日,在内蒙古锡林郭勒盟西乌珠穆沁旗的典型草原上研究了狭颅田鼠(Microtus gregalis)冬季集群与来自艾虎(Mustela eversmanni)的捕食风险。采用鼠洞口数量作为狭颅田鼠集群大小的指标,分析了艾虎对不同大小狭颅田鼠集群的捕食优先选择偏好。对实验样地内狭颅田鼠的洞群洞口数进行了调查统计(样地内总共涉及102个狭颅田鼠有效洞群),并计数此期间的艾虎粪便堆数以及攻击掘开狭颅田鼠洞群的情况。运用非参数的Mann-Whitney U检验法进行数据分析,结果表明:从艾虎遗留的粪便痕迹来看,没有被艾虎访问过的田鼠洞群与被艾虎访问过的洞群之间差异达到极显著水平;另外,从狭颅田鼠洞口被艾虎掘开的痕迹来分析,没有被艾虎挖掘的洞群与被艾虎挖掘的洞群之间的差异也达到极显著的水平;另外,随着田鼠洞群洞口数量的增加,出现艾虎粪便和掘洞的频次和概率就越高。表明艾虎对狭颅田鼠集群洞口数的选择差异性非常显著,明显倾向于选择在洞口数量多的狭颅田鼠洞群停留,同时也更倾向于掘开洞口数量较高的狭颅田鼠洞群作为捕食对象。

Relationship between predation risk and group size of narrow-skulled vole in the typical steppe of Inner Mongolia

Group sizes of overwintering colonies of narrow-skulled voles (Microtus gregalis) may affect predation risk by mammals. We examined the effect of different social group sizes on the predation risk of narrow-skulled voles in the Xilinguole typical steppe, Inner Mongolia, West Ujimqin Banner, from September 15 to 30, 2005. Furthermore, we examined the effects of predation by the steppe polecat (Mustela eversmanni) on the group size of the narrow-skulled vole within the sampling area. The number of narrow-skulled vole colonies was used to estimate group sizes of voles. The number fecal droppings and holes excavated by steppe polecats within the habitat of each narrow-skulled vole colony were recorded as indicators of predation pressure. A total of 102 voles were observed within the sampling area. The nonparametric Mann-Whitney U test was used to detect differences in social group sizes between the colonies with and without signs of polecat activity. The results showed that the rank sum of the colonies not surrounded by polecat feces was 3273.5, whereas colonies surrounded by polecat feces was 1,979.5 (U=113.5, Adjusted Z Value=-6.387, Adjusted P < 0.001). The rank sum of colonies with holes dug by polecats was 556, whereas the rank sum of colonies without the polecat excavation was 4697 (U=41, Adjusted Z Value=-3.525, Adjusted P=0.0004). The results of the 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 sizes. This difference indicated that the steppe polecat significantly preferred narrow-skulled vole colonies with high group sizes. The polecats tended to spend longer periods around colonies with several burrow entrances. Some polecats even attempted to dig out such colonies, and therefore, several fecal droppings and excavation trails could be found around these colonies. This finding indicated that the colonies with larger social group sizes experienced higher predator risk.