Agricultural practices improve breeding success of indigenous frogs in restored rice paddies: A case study from the Miyajima Wetland, Japan

Rice paddies have played an important role as a substitute habitat for wetland species. However, environmental changes and the abandonment of rice paddies have led to a decline in the number of wetland species. Moreover, rice paddies are vital habitats for sustaining the population of pond-breeding frog species. However, it remains unclear how agricultural practice influences the sustainability of frog species. In this study, we conducted surveys in 13 restored rice paddies with different management histories and one irrigation pond in the Mikajima Wetland to investigate the characteristics of the rice paddies and the relationship between the characteristics and breeding success of the Japanese brown frog ( Rana japonica ). We found 134 egg masses at 14 sites, and monitored them until they hatched, died, or were lost; environmental factors, such as water temperature and depth, were recorded. First, we conducted a principal component analysis to determine the study site characteristics. Second, we constructed generalized additive mixed models to investigate the relationship between environmental factors and the number of new egg masses, hatching success, and number of days until hatching. Our results showed that the study sites were characterized by environmental factors associated with common management practices, irrigation and weed control. The breeding success of R. japonica was related to various aspects of aquatic habitats alternating between agricultural practices, and therefore, the agricultural practices can be practical measures for improving the environmental conditions in rice paddies to create preferable breeding and egg-rearing habitat for R. japonica .