Long-Term Trends toward Earlier Breeding of Japanese Amphibians

Recently, declines in amphibian populations all over the world have been reported. Global warming has the potential to become one of the most important causes for those declines, because reproductive activities of amphibians are affected severely by temperature and rainfall. It has been reported that climate warming has promoted a long-term tendency toward earlier breeding among amphibian populations in Europe and North America. However, some studies have not supported such a long-term change in the timing of amphibian breeding in those areas. We analyzed long-term data sets (12- to 31-year period) on the date of first spawning for four populations of three Japanese amphibians (Hynobius tokyoensis, Rana ornativentris, and Rhacophorus arboreus) in the suburbs of Tokyo and detected a significant trend toward earlier breeding in all populations examined. We also detected that the date of first spawning was correlated strongly with the mean monthly temperature just before the breeding season for each population examined. Given that the long-term trend of warming in the study district was significant, our investigation demonstrated that climate warming has affected the timing of breeding in at least some species or populations of amphibians in East Asia.