千岛湖秋季社鼠种群年龄结构及繁殖状况初探

Age-structure and reproduction investigation on Niviventer confucianus living on islands at Qiandao Lake in autumn

2007年9～11月，对千岛湖不同类型岛屿捕获的123只社鼠的年龄结构及繁殖状况进行研究，结果表明：9—10月为千岛湖区社鼠种群的繁殖高峰期，较同纬度其他地区早。雌鼠从亚成年组出现怀孕个体，雄鼠较雌鼠性成熟早，幼年组已出现睾丸下降个体。大、中、小型岛屿年龄结构不同，分别为稳定型、衰退型及增长型。岛屿大小能够对社鼠种群繁殖指标产生影响，大型岛屿雌鼠繁殖指数（1．96）与平均胎仔数（4．9±0．35只）及雄性个体睾丸下降率（50．0％）均较高，社鼠种群稳定；中型岛屿雌鼠的繁殖指数（3．45）与平均胎仔数（5．17±0．42只）为3种类型岛屿中最高，并且雄鼠的睾丸下降率（64．7％）也相对较高，有利于社鼠种群数量增加；小型岛屿雄鼠的睾丸下降率虽然最高（68．4％），但雌鼠繁殖指数（0．75）与平均胎仔数（4．00±1．53只）均较低，且参与繁殖的主体成年组性比（10：5）失调，种群易出现波动。另外，社鼠的繁殖情况与植被类型和人为干扰也有较大的关联。

Niviventer confucianus, the main pest rat at Qiandao Lake, were canght in their preferred woodland habitat on islands in the lake. We captured 123 individuals from September to November, 2007, and brought them back to our laboratory where they were marked, measured for morphological characteristics, and then necropsied to determine sex, age and reproductive condition. Specimens were assigned to four age classes on the basis of body length ： juvenile group （ body length≤110 mm） , sub-aduh group （body length from 111 - 125 mm） , adult group （body length from 126 - 150 mm） and elder-adult group （body length ≥ 151 mm ）. Males and females demonstrated no difference in body size and could be classified with the same standard. Most of the rats bred in autumn with a reproductive peak from September to October. Most reproduction occurred in the adult and elder-adult groups. Reproductive condition was significantly influenced by vegetation coverage and human disturbance. The index of reproduction and the average number of embryos were highest in the medium-sized islands （ 3.45, 5. 17 ± 0.0. 42 ） and lowest in the small islands （0. 75, 4. 00 ± 1.53 ） , with values from the large islands in between （ 1.96, 4.9 ± 0. 35 ） . By contrast, the rates of scrotal testes decreased as the size of island increased, with 68.4% in the small islands, 64. 7% in the medium islands and 50.0% in the large islands. Although age structure declined in the medium island populations, adults were the main reproductive group, and the population size increased after the reproductive season. The sex ratio （M/F） of adults was maladjusted in the small islands. Therefore, the population was stable in the large islands, higher in the medium islands, and fluctuating in the small islands.