Mosaic land use in agricultural landscapes maintained organisms with complex life circle, such as frogs, but in a few decades, increasing of abandoned rice fields is considered to reduce these organisms. Abandoning takes away their breeding habitats through drying. It was reported that, on the other hand, abandoned rice fields supplied prey to them, which may induce a positive effect of abandoning rice fields on their population sizes. Therefore, the effects of abandoned rice fields on frogs are considered to depend on the relative strength between habitat loss and resource availability. Here, we report that landscape structure surrounding rice fields determines the effect of abandoned rice fields on densities of Black-spotted pond frog Rana nigromaculatain.

We investigated the frog density in two types of landscape in Akita prefecture; one is middle mountainous areas and the other is plain fields. Analysis of Generalized Linear Models showed that edge lengths of abandoned rice fields have a positive impact on frog densities in plain fields, while abandoned rice fields affected negatively in middle mountainous areas. Frogs in middle mountainous areas consumed prey more from forest than abandoned rice fields. Our results suggest that landscape dependence of abandoning effects on frogs is caused by difference of prey amount supplied from forest and abandoned paddy fields.