Effects of multiple stressors on amphibian oviposition: Landscape and local determinants in central Japan

Abstract

Amphibian declines are caused by multiple stressors at the landscape and local levels, resulting in habitat loss, fragmentation, splits, and degradation. However, the combined effects of different landscape scales on the amphibian declines are poorly understood. We examined the breeding distribution of three frog species, Rana japonica, Rana ornativentris, and Bufo japonicus formosus, along an ecological gradient from urban to mountain areas. The number of egg masses and data on landscape and local variables were collected at 124 sites in Toyota, Okazaki, and Shitara, central Japan. The best model with the lowest value of the Akaike Information Criteria (AIC) was obtained using landscape variables at a 500-m-radius buffer for all three species. The number of egg masses increased with forest area for all frog species. Yet, other variables differently affected the number of egg masses of three species at each site. The egg-mass number of R. japonica was positively affected by the residential region with much vegetation area & elevation difference, and negatively affected by elevation. That of R. ornativentris was positively influenced by the abandoned paddy-field, and negatively influenced by the total road density. Regarding B. japonicus formosus, its egg-mass number was positively affected by the residential region with much vegetation area, and negatively affected by elevation difference. At the local scale, the water area positively affected the number of egg masses of all three species, while the percentage of concrete revetment has negative effects. This study not only assesses how the assemblage of frogs respond to different habitats at multiple spatial scales along the land use gradient (urban-mountain), but also emphasizes the importance of strategic management actions in agricultural landscapes, allowing the maintenance of habitat diversity for amphibians.