布氏田鼠种群繁殖特征研究

STUDY ON POPULATION REPRODUCTION OF BRANDT'S VOLES (MICROTUS BRANDTI)

越冬田鼠每年可繁殖3胎,第1胎幼仔生于4月下旬到6月上旬,第2胎幼仔生于5月中旬到7月上旬,第3胎幼仔生于6月中旬到7月下旬。种群上升年份(1987)各胎幼仔出生高峰比1988年的提前10天左右。1987年越冬鼠第1胎集中,如4月下半月,1987年怀孕率为100％,而1988年只有44.44％。6月上半月以前越冬鼠为种群繁殖的主体,而后被当年生鼠所取代。从4月下半月到9月上半月共出生4批同龄群。K_1 和K_2 组生长发育旺盛,当年就参加种群繁殖,可怀孕1—3胎。K_3组生长发育较慢,当年并不性成熟,越冬后性成熟成为种群越冬鼠的主体。K_4出生晚,数量少,很少能度过漫长寒冷的冬季而成为种群的无用或潜在的繁殖力量。本文还发现越冬鼠的平均胎仔数显著高于当年鼠;种群上升年份越冬鼠平均胎仔数高于种群下降年份,而当年生鼠的平均胎仔数年度间则没有显著性差异。

The overwintering voles can reproduce three litters. The first litter was born from Late April to Early June. The 2nd from Middle May to Early July and the third from Middlel June to Late July. The peaks of birthday curve of each litter in population-increasing-year (1987) were ten days earlier than those of population-decreasing-year (1988). The ratio of pregnant voles to all females was 100% in Late April of 1987. But the ratio in Late April of 1988 was only 44.44%. The overwintering voles played main part in population reproduction before Early July from percentage of overwintering pregnants to all pregnants. Then the voles bron of this year replaced overwintering rapidly. Four cohorts were produced from Late April to Early September. The 1st cohorts (K1) and K2 grew and matured rapidly. Those voles can be reproduced 1-3 litters and most of K1 and K2 disappeared from population. K3 delayed sexual maturation and enter winter as sex-non-maturing voles.Though body mass and lenghth increased, the sexual organs remained dormant, resumed growing in late winter or early spring and became the breeding population as overwinterings in Early April. K2, a small number of voles,very few survived the long and cold winter or reproduced. The mean litter size of overwinterings was higher than that of the voles born of this year significantly. The mean litter size of population-increasing-year was significantly higher than that of population-decreasing-year. There were not significant difference of mean litter size of the voles born of this year between 1987 and 1988.