Although the Three Gorges Project(TGP)may have affected the population structure and distribution of plant and animal communities,few studies have analyzed the effect of this project on small mammal communities.Therefore,the present paper compares the small mammal communities inhabiting the beaches of Dongting Lake using field investigations spanning a 20-year period,both before and after the TGP was implemented.Snap traps were used throughout the census.The results indicate that the TGP caused major changes to the structure of the small mammal community at a lake downstream of the dam.First,species abundance on the beaches increased after the project commenced.The striped field mouse(Apodemus agrarius)and the Norway rat(Rattus norvegicus),which rarely inhabited the beach before the TGP,became abundant(with marked population growth)once water was impounded by the Three Gorges Reservoir.Second,dominant species concentration indices exhibited a stepwise decline,indicating that the community structure changed from a single dominant species to a more diverse species mix after TGP implementation.Third,the regulation of water discharge release by the TGP might have caused an increase in the species diversity of the animal community on the beaches.A significant difference in diversity indices was obtained before and after the TGP operation.Similarity indices also indicate a gradual increase in species numbers.Hence,a long-term project should be established to monitor the population fluctuations of the Yangtze vole(Microtus fortis),the striped field mouse and the Norway rat to safeguard against population outbreaks(similar to the Yangtze vole outbreak in 2007),which could cause crop damage to adjacent farmland,in addition to documenting the succession process of the small mammal community inhabiting the beaches of Dongting Lake.
The outbreak of Yantze vole ( Microtus fortis) population in Dongting Lake region is closely related to the evolvement of lake beaches,because the deposition of lake sediments results in the expansion of lake beaches,which provides the possibility of the increase of the vole's population. Reclaiming farmland from lake via building cofferdams,eliminating snails by building cofferdams for eradicating schistosomiasis,and over-hunting predators in the region cause the voles becoming a pest after the 1970s. In recent years,the Three Gorges Project and the conversion from farmland into lake have had deep impacts on the environment in the lake region. The dispatching of the down flow rate by the project has induced the expansion of the low and medium level beaches in the lake region,while converting farmland into lake directly has induced the expansion of the lake beaches,both of which have expanded the potential habitats of the vole's population. Therefore,more attention should be paid to the quantitative variation trend of the vole's population in the future.
