- 農村計画学会誌 (ISSN:09129731)
- vol.24, no.2, pp.91-102, 2005 (Released:2007-03-01)
In this research, in order to clarify ecological significance of the levees in flatland paddy fields, the habitat density of the frog, Rana porosa porosa on each levee type was investigated. The investigation was conducted in the Isawa area in the southern part of the Iwate pref. in the early summer in 2002. The number of Rana porosa porosa in the paddy fields that were rearranged to large units in the recent years, has decreased. It has been suggested that the disappearance of traditional earth waterways and the reduction of levees might have caused the decrease of the frog species in the paddy fields. Our research shows that on the levees attached to waterways the number of the frog species significantly varies according to the material that is used for the waterway. That is, the number becomes smaller when it was altered to concrete from the naked soil. At the same time, we did not find any significant difference in the amount of food for this frog species between in the concrete waterways and in the earth waterways. This suggests that the amount of food does not cause the discrepancy between the number of the frog species in the concrete waterways and the number of one in the earth waterways. On the levees between the paddy fields in the area that was consolidated before the recent consolidation, the number of the frog species considerably varies according the moisture condition of the area. This indicates the importance of levees as pieces of land in water, narrow walkways between paddy fields that are filled with water. As opposed to the levees between paddy fields, the levees attached to earth waterways hold high density of the frog species. This verifies that Rana porosa porosa have an affinity to the levees attached to the earth waterways. The significant factors of how this frog species choose what kind of levees to frequent, are more structural, i.e., the structural changes of the paddy fields that are caused by the modern farmland consolidation, the existence of attaching waterways and the material of the waterways, than administrative, i.e., water management and weeding. Also, we verified that the amount of food is not especially a regulative factor in terms of the density of the frog species on the levees.