Abstract: The population dynamics of Microtus fortis in Yueyang, Hunan Province was studied from 1991 to 1996. M. fortis lived on the beach of the lake from early autumn to next spring, but moved to the farmland in summer when the beach was flooded. When lived on the beach, its population increased gradually. Usually, M. fortis made great damage on the crops when moved to the farmland. The population dynamics of M. fortis was different on the beach and on the farmland, and the key affecting factors were also different. Lake beach was the most suitable habitat for M. fortis. When it emerged in autumn, M. fortis moved back on it. The main breeding season of M. fortis inhabited on the beach was from October to May, and its population density increased gradually. The period between the beach emerged and been flooded determined the population size of the animal moved to farmland. Another factor was the rainfall in March. Farmland was not the suitable habitat for M. fortis. Because of the low breeding potential, high mortality and dispersal on farmland, its population density kept decreasing, and was very low in winter. The population density on farmland dropped dramatically when the lake beach emerged. The animal population was forecasted by means of regression analysis, and a linear regression equation was obtained. The predicted values matched with the real population densities of the animal in the field.

Key words: Microtus fortis, Population dynamics, Dongting Lake region, Forecast