earticle

영어

Although amphibians are declining worldwide and there is valid focus on determining the causes, critical basic information is missing for many species, such as geographic distribution and rate of population decline. In Korea, there are two closely related treefrog species: H. japonica, which is distributed widely throughout the country, and H. suweonensis, which occurs sympatrically in a narrow strip of western coastal plains. H. suweonensis is only found within the distribution of H. japonica. Males of both species call to advertise for mates, and the calls are distinguishable. To determine the spatiotemporal distributions of H. suweonensis and H. japonica, we conducted a calling survey in 70 localities encompassing the distributional range of H. suweonensis. A group of volunteers conducted the survey, supplemented with recording calls for validation. Calling activity was scored using the calling index (CI), which ranged from 0 to 3, with 0 indicating no calling and 3 indicating full chorus. The endangered H. suweonensis was found only in 14 out of 70 localities, designated as syntopic, whereas H. japonica occurred in all 70 localities. The calling activity of H. japonica was vigorous, with 56.1% of all surveys registering CI of 3 throughout the study period, but the calling activity of H. suweonensis was faint, with only 13.4 % of all surveys registering CI of 1 or higher. Geographic information system analysis revealed that syntopic localities had significantly less urban and forested areas and significantly more rice paddy area than the non-syntopic localities. Binary logistic regression confirmed that three habitat factors had negative effects on the occurrence of H. suweonensis: the percentages of urban, agricultural field, and forested areas. The spatiotemporal distributions of the two treefrog species throughout the breeding season confirmed that H. suweonensis indeed rare and may be undergoing an extinction vortex. For the conservation of H. suweonensis, swift and decisive measures should be taken, including determining the causes of population decline and establishing protected habitat areas.