Abstract
We characterized the influence of patch- and landscape-scale environmental factors on the distribution of the endangered Tokyo Daruma pond frog, Rana porosa porosa, which inhabits paddy fields in suburban areas with developmental expansion. We surveyed paddy fields at 146 sites in the cities of Kunitachi and Fuchu, Tokyo, Japan, for frog-mating calls and environmental factors from 2009-2010. In addition, we calculated the paddy field area and proportion of the area of other paddy fields within a buffer area, which was generated from the peripheral edge of the paddy fields by geographic information systems. The presence of pond frogs was confirmed at 53 sites. Through multiple logistic regression analysis using a generalized linear model as well as all measured patch- and landscape-scale environmental factors, a model comprising an area of paddy fields, vegetation cover in levees, water flow during the non-irrigation period, soil canals, and proportion of the area of paddy fields within a 300-m buffer area, was selected as the best model for describing the occurrence of pond frogs. Every factor within the best model exhibited a positive relationship with the occurrence of pond frogs. These results suggest that both patch- and landscape-scale factors may affect the distribution of pond frogs. The area size of paddy fields is expected to be a particularly important factor affecting the distribution of pond frogs in suburban areas, as paddy fields tend to be fragmented and narrowed by urbanization. Moreover, improving habitat quality via the growth of vegetation in levees, maintaining canal water flow during the non-irrigation period, maintaining soil canals, and preventing habitat fragmentation, would contribute to the conservation of pond frogs.
