| During autumn 2007 and spring 2008,we surveyed 14 islands and 2 peninsulas for small mammals in the Thousand Island Lake region to determine the effects of the habitat fragmentation on the Age-structure,reproduction investigation,Relative fatness of Niviventer confucianus and the community distribution pattern and community diversity of the small mammals.The main results of our studies are as follows:Niviventer confucianus,the main pest rat in Qiandao Lake,were caught in their preferred woodland habitat.We captured 123 individuals from September to November in 2007,brought them back to our laboratory,where they were marked, measured morphological characteristics,and then autopsied to determine sex,age and reproductive conditions.Specimens were assigned to four age classes on the basis of body length:juvenile group(body length≤110mm),sub-adult group(body length from 111～125mm),adult group(body length from 126～150mm) and elder-adult group(body length≥151mm).Males and females had no difference in body size,and could be classified with the same standard.Most of the rats bred in autumn in our study,so the reproductive pear was in autumn(September to October).Also we found that the adult and elder-adult groups were the main reproductive groups.The reproductive condition was significantly influenced by vegetation coverage and human disturbanceThe index of reproduction and the average number of embryos were highest in the medium island(3.45,5.17±0.0.42) and lowest in the small island(0.75, 4.00±1.53),with the large island in between(1.96,4.9±0.35).By contrast,the rates of scrotal testes decreased as the size of island increase,with 68.42%in the small island, 64.71%in the medium island and 50%in the large island.Although age structure declined in the medium island,the adult was the main reproductive group,and the population size increased after reproductive season.The sex ratio(M/F) of adults was maladjusted in the small island.Therefore,the population is stable in the large island, rising in the medium island,and fluctuating in the small island.There are significant differences between diversity index,evenness index and dominance index and the preponderant species changed in the 14 islands.Through the analysis of stepwise linear regression of factors that may influence species diversity of islands,such as:area,distance to the nearest mainland,distance to the nearest bigger island and plant species richness,we discovered that only plant species richness had significant effect on the species richness of small mammals.16 samples were classified by the constituent proportion of species,Xuyuan and 14 islands were the same kinds,and Yaojia was the other one,the similarity index also supports this result. In Thousand Island Lake region,habitat fragmentation resulted in the declined stability of ecosystems and the violent variety of community diversity when season changed.With the increase of the size of the islands,the small mammals' species richness doesn't always increase but shows small island effect,we also found that the constituent proportion of species in 14 islands was close to Xuyuan.It can be concluded that they belonged to one fragment habitat before the reservoir had been formed.The small mammals present a non-random pattern in assemblage;It had a significant nested pattern on the islands that was influenced by plant species richness and habitat specificity of the species;The differences in sampling intensity can result in a considerable overestimation of the degree of nestedness,which we should aviod it in the research.Here is the conclusion:In Qiandao Lake,the community pattern of the small mammals was influenced by plant species richness and habitat specificity.This two factors make the species with high adaptability can survive in the various environment and the ones with low adaptability only can survive in particular environment.All this make the pattern of the small mammals in Qiandao Lake shows nestedness.
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