The Research On Population Dynamics And Structure Of Niviventer Confucianus In Land-Bridge Island

We used capture-mark-recapture (CMR) method to live-trapp two Niviventer confucianus populations on A island and B island in Thousand Island Lake region in Chunan County, Zhejiang province from October2009to November2010, studied the applicability of different estimation methods in white-bellied rat population sizes on land-bridge island, and analyzed the population dynamics, population survival rate and population turnover rate, age structure, sex ratio, and effects of climate factors on the populations. Then, we discussed the impact of habitat fragmentation on the population dynamics and population structure of Niviventer confucianus. The main results were the followings:1. We used Jolly-Seber method, modified Lincoln index method, Schnabel method and minimum number of animals alive (MNA) method to estimate population sizes of Niviventer confucianus. The results showed that there was no significant difference between Jolly-Seber method and modified Lincoln index method. In the field, the data from CMR don’t always meet the conditions of Jolly-Seber method, and the method can not estimate the size in the first and last months, so we considered that modified Lincoln index method was more suitable for estimating the population quantity of Niviventer confucianus in the land-bridge island.2. The two populations sizes of Niviventer confucianus began to decceased when the number was over50, and it showed that the similar islands have similar environmental carrying capacity. That was the reasons A and B population sizes declined in June and April, respectively. The impact of inter specific competition and predation on B population was greater than that on A population, which caused B population decline faster than A population after June. The results were similar to the previous findings of the region, but inconsistent with the results on Tianmushan and Beishan. We though that the island and the terrestrial environment showed different effects on the seasonal fluctuation of the Niviventer confucianus population.3. According to the age structure of two populations, the dominant groups were the juvenile and sub-adult groups in the first half of the year, while they changed into the adult and old-adult groups after half the year. Juvenile group began to appear in October and November, and the high proportion of juvenile group in the March and April, so the population growth reached the peak in the first half of the year. Because of Aging, the population eventually declined to the low size after half the year. According to the comparisons, age structures of the populations were inconsistent with that on Tianmushan, and the land-bridge island environment appeared a certain effects on the age structure of Niviventer confucianus populations.4. There were significant negative correlation between the population quantity and sex ratio. When the population sizes reached the peak, the females were less than males. Nevertheless, when the population sizes were low, the female were more than males. We considered that in the process of population growth, the females were more important than males, but when the population sizes declined, the survival of the males was greater than females.5. The Chinese white-bellied rats breed mainly in September and October, March and April, few individuals breed from May to August, and stopped breeding in November. The average litter size of Niviventer confucianus in medium-sized island was significantly higher than that in Jinhua region from September to October. We considered the reason was the special enviroment on island. Because of the high breeding rates in September and October, the population reached to a higher level in the second year in March.6. The turnover rates were very low in the two populations. Because of the lack of immigration and emigration in the land-bridge islands, population quantity had some influences on the population survival and the survival rates of males and females, and the survival rate of overwintering individuals played an important role in population fluctuations. According to the study of the residence time in Niviventer confucianus, we hypothesized that the ecological life might be only one year, and because of the poor living conditions in land-bridge islands, the life was significantly shorter than the results in the past studies.7. It was beneficial to maintenance and growth for Niviventer confucianus populations when the monthly average temperature was10℃-22℃, and it was unfavorable when the monthly average temperature exceeded22℃. The high temperatures and drought might lead to the population decline and the fluctuations of sex ratio in summer. The climatic could not afford a fundamental role in the decision on the population dynamics, while sex ratio and fecundity of the population were the the key factors to adjust population sizes.