Effects of Landscape Heterogeneity at Multiple Spatial Scales on Paddy field-breeding Frogs in a Large Alluvial Plain in Japan

Enhancing the environmental heterogeneity of habitats is essential to decelerate the degradation of biodiversity in rice paddy ecosystems caused by the recent rapid changes in agricultural landscapes. However, paddy field environments hierarchically belong to agricultural landscapes and river basins. Therefore, the spatial scale of environmental heterogeneity affecting the distribution patterns and abundance of the organisms inhabiting paddy fields, such as frog species, varies. Thus, in the Kanto Plain, the largest alluvial plain in Japan, we conducted an extensive frog survey to ascertain multiple spatial scale heterogeneities of frog abundance in relation to topography, climate, land use pattern, and features of paddy fields. Across 200 field sites, five frog species were detected during calling surveys. The statistical, niche and abundance models revealed differences in distribution patterns, spatial heterogeneity of abundance, and environmental preference of these frogs at the spatial levels of river basins, landscapes, and paddy fields. While the distribution pattern and abundance of Zhangixalus schlegelii were affected by the percentage of forest area, those of Pelophylax porosus porosus were sensitive to features relating to water availability of the paddy fields. Despite the small diversity of species detected, the presence of two species with unique habitat preferences revealed significant benefits of habitat heterogeneity in the agricultural landscape, allowing us to suggest management strategies for improving frog diversity in agricultural landscapes dominated by paddy fields.