北京地区黑线姬鼠种群年龄和繁殖的研究

ON THE POPULATION AGE AND REPRODUCTION OF Apodemus agrarius IN BEIJING AREA

1982—1986年,作者在北京农业区研究黑线姬鼠种群的年龄和繁殖,共解剖标本1360号(684,676)采用胴体重划分出4个年龄组,研究睾丸重量与性成熟的关系,确定睾丸重0.5克为性成熟线。种群一年更新一次,个体年繁殖2—3胎,当年出生的鼠基本不参加繁殖,胎仔数有年度差异,1982年为6.18±0.35,1983年为5.29±0.13,1984年为5.97±0.13,1985年为5.69±0.20。

The popalation ecology of Apodemus agrarius in the rural area of Beijing was in-vestigated from 1982 to 1986. A total number of 1360 specimens were collected and dissected, among which 684 were males and 676 females. 1. Age s ructure in population ( 1 ) Division of the age groups:the specimens were divided into four age groups- based on thfir body weight excluding viscera as the major index. The body weight of group Ⅰ was≤10g; group Ⅱ 10.1 -16.9g; group Ⅲ 17-24.9g; group Ⅳ>25g. (2) The seasonal fluctuation of the age structure in populations: on the basis of analysing our five years trapping data from January to February, we found there were no individuals belonging to the groupⅣ in the population of this area. From March to April, the proportion of group Ⅲ increased and group Ⅰdecreased. From May to June, the individuals of group Ⅳ began to appear and increased in number suc-cessively; while the proportion of groupⅠ andⅡ was remarkably low. During the months of July and August, the proportion of group Ⅳ , i.e., the individuals of the overwintering mice increased, while the individuals of that year belonging to the groupⅠ andⅡ reappeared and increased in number. Group Ⅳ decreased in number from September to October, due to the death of the overwintering mice. In November and December, the main compositions were the individuals of group Ⅱ and group Ⅰ , while individuals of group Ⅳ were rarely seen. So we can draw a conclusion that the population structure of Apodemus agrarius renews once a year in the area. 2. The sex ration: It was approximately 1:1 on the whole, but > in groupⅠ and Ⅱ, and > in group Ⅲ and Ⅳ. 3. The breeding ecology in population (1) The breeding characteristics of the males. Studies have been carried out mainly on the correlation between the weight of testis and the sex maturity. The 0.5g weight of testis was determined as the landmark cf sex maturity, and according to the criteria, no adult males were observed in Beijing area from January to February. In March and April, the population was mainly composed of group Ⅱ and Ⅲ, with most individuals being mature. From May to June, the population was composed of indivi-duals of group Ⅲ andⅣ, and all the individuals were sex mature ones. A small num-ber of juveniles of group Ⅲ were making their first appearance from July to August. From September to October, the population was mainly composed of individuals be-longing to group Ⅱ andⅢ, and most of them reached sex maturity, and atrophied were seen in groupⅣ. In November and December, the population comprised four groups, and only a few individuals of group Ⅳ were seen with atrophied testes, while the three other groups were all immature. These results indicated that there were two peaks of the reproduction in May-June and July-August, and the latter was the main period of reproduction, and what is more, the males in the year generally did not reach maturity. (2) The breeding characteristics of females: The studies covered the following aspects: 1) The velocity of the sex maturity: In April months of 1983-1985, there were 20.8-54.1% femaes entered the beginning of the breeding season, and the first young entered the population late after May, but most of them did not take part in reproduction. The presence of embryo were noted only in few individuals in Septem-ber and October. 2) Annual cycles of reproduction and the ecological Life-span: There were two pregnancy periods per year, and a part of the individuals were seen to be pregnant three times. The population renewed once a year fundamentally. The ecolo-gical Life-span maintained about one year. 3) The litter size varied annually with little fluctuation, it being 6.18 ± 0.35 in 1982, 5.69 ± 0.13 in 1983 and 5.97 ± 0.20 in 1985.