Abstract
The research on the relationship between the environmental conditions of the habitat and the species and the individual number was made in respect to the frogs which inhabiting in the Kashima and Tegri River, watershed of Inba Marsh, Chiba Prefecture. The field-survey was carried out from May to July in 1997 and 1998. Walking on the paddy field ridge, the number of the frogs, the walking distance and the environmental factors of the surrounding area were recorded. Then the relationship between the individual density of each species and the environmental conditions was analyzed by means of Hayashi's quantification theory I.
As a result, the major factors which would affect the individual density were clarified: The underdrainage of the paddy field, the landuse of the slope, the irrigation system and the arrangements of the canal. Another fact was also revealed that the reformation into well-drained paddy field which is promoted by the farmland consolidatuin tends to have the negative impact on the inhabiting of the Japanese brown frog while it does not have much affect on that of the Japanese tree frog.
