Abstract: Reproductive capacity of small mammals is affected by many factors, such as climate, habitat and social stress, etc.  Population density is one of the key factors that affect the reproductive capacity of female rodents. However, little has been reported on the effect of breeding under existing different population densities and different durations. Here, we compared the reproduction of adult Microtus fortis at different densities for long or short durations. We selected 144 adult voles, which were randomly divided into 4 groups (sex ratio 1:1): 2 voles per cage and housing for 90 days [group LL (low density, long time)], 8 voles per cage and housing for 90 days [group HL (high density, long time)], 8 voles per cage and housing for 20 days [group HM (high density, middle time)], 8 voles per cage and housing 10 day [group HS (high density, short time)]. Then one male and one female animal from the same group were randomly paired. The litter size, pregnancy rate, pregnancy frequency and farrowing interval were recorded every day until 180d. The experiment data were analyzed in 3 periods: the first stage was 0-90d (the treatments under different densities and different housing time), the next stage was 90-109d, (The transition period)，and the last stage  was from 109d on (normal pair breeding period). One-way analysis of variance (One-way ANOVA) was used to analyze the mean litter size, and a Chi square test (χ²) was used to compare the frequency data. Results showed that the mean litter size decreased significantly after a long period of high density treatment. No significant differences have been found among groups in mean pregnant frequency. The pregnancy rates significantly increased from group HL to group HM and then to group LL and HS. In the first stage, breeding was found only in group LL. The pregnancy rates in the transition period were significantly different among the groups, the values of group LL and group HS were significantly higher than group HL. The mean litter size of group HS was the highest, that of group HL was the lowest, and there were no significant differences among groups. The pregnancy rates and mean litter size in the last stage were significantly different among the groups, and the values of group LL and HS were always higher than group HL and HM. No significant differences had been found among groups in the mean pregnant frequency, mean litter size and the farrowing interval. Taken together, there were great differences in density-dependent effect for different durations. For Microtus fortis, reproduction was more inhibited by a 20d-high-density environment than a 10d-high-density environment. After the recovery of low density, the hysteresis effect of population density constraints exists.

Key words: Density-dependent, High-density treatment, Microtus fortis, Reproduction

摘要： 本研究中用成年东方田鼠不同时间不同密度笼养后（笼内雌雄各半），低密度配对饲养，观察各阶段东方田鼠繁殖指标的差异。试鼠144只，处理时分为LL（低密度长时间）（2只/笼，共20笼，90d）、HL（高密度长时间）（8只/笼，共5笼，90d）、HM（高密度中等时间）（8只/笼，共4笼，20d）与HS（高密度短时间）（8只/笼，共4笼，10d）4组。处理后在低密度条件下观察繁殖情况（胎仔数、怀孕率、分娩频率以及产仔间隔等），直至180 d。实验数据按时间划分为3个部分统计：0~90 d为第一阶段(不同密度处理期)，90~109 d为过渡阶段（处理后的过渡期），109 d以后为第二阶段（正常低密度配对繁殖期）。结果表明：经过长时间高密度处理后，平均产仔数显著减少，组间平均分娩频率无显著差异。怀孕率由HL组到HM组，再到LL和HS组显著增加。在第一阶段，除了LL组之外，其余各组都未发现繁殖。过渡阶段的怀孕率组间差异显著，LL组以及HM组显著高于HL组。第二阶段的怀孕率以及胎仔数的组间差异显著，都为LL、HS两组较高，HL、HM两组较低。平均分娩频率、平均胎仔数以及产仔间隔各组间无显著差异。结论：不同持续时间的密度效应有较大差别。对于东方田鼠，20d的高密度处理相比于10d更能对其繁殖起到抑制作用。恢复低密度后，存在种群的迟滞性密度制约。

关键词: 东方田鼠, 繁殖指标, 密度制约, 迟滞效应