In the present study, major habitats of herpetofauna species were predicted using distribution models of 19 amphibian and 20 reptile species inhabiting South Korea. A high correlation was identified between important climatic variables in the areas where herpetofauna species were distributed and geographical variables, and altitude was found to be an environmental variable with a major influence on their distribution. As a result of hotspot area predictions, the province with the most diverse species was Gangwon-do, around the Taebaek Mountains.
Altitude was an important environmental factor affecting the distribution of herpetofauna species, showing a high contribution in most models. In general, different herpetofauna species are distributed at different altitudes because of their limited home ranges and habitation environments, and altitude, among various environmental variables, is known to have a major influence on their distribution[7, 27, 29, 30]. The preferred altitude range is known to vary among the herpetofauna species distributed in South Korea (Table S2)[7, 25]. For example, while most of the 19 amphibian species are mainly distributed at altitudes between 0 m and 500 m, three species, namely Kaloula borealis, Rana plancyi, and Hyla suwonesis, are known to prefer low altitudes between 0 m and 100 m, whereas three species, namely Bufo stejnegeri, Onychodactylus fischeri, and Rana huanrenensis, are known to prefer high altitudes between 400 m and 700 m[25, 30, 44]. Most of the 20 reptile species are mainly distributed at altitudes between 0 m and 500 m, except for the following three species: Eremias argus, which is known to prefer low altitudes between 0 m and 100 m, and Gloydius intermedius and Scincella huanrenensis, which are known to prefer altitudes higher than 400 m[7, 29, 34]. The results of the present study were consistent with the elevation distributions for herpetofauna species reported in previous studies.
We found that herpetofauna species distributed in South Korea preferred forests and farmland, with amphibians more commonly inhabiting farmland and reptiles more commonly inhabiting forests (Fig. 2b). Paddy wetlands provide an essential aquatic environment for skin-breathing amphibians, and 16 of the 19 amphibian species inhabiting South Korea, except for Kaloula borealis, Rana plancyi, and Karsenia koreana, use paddy wetlands as breeding grounds[28, 30, 58–60]. Furthermore, among these 16 amphibian species, all but two species, Rana plancyi and Hyla suwonesis, are known to prefer paddy wetlands located near mountainous areas rather than plains, and their population size is also known to be larger than that of the other two species[27, 30, 60, 61]. Among the 20 reptile species, all but two species, Eremias argus and Gekko japonicus, are known to prefer forests, using rivers, valleys, ridges, grasslands, wetlands, and other habitats in the surrounding areas for breeding and hibernation[29, 34, 62–66]. Furthermore, 18 out of 20 reptile species, excluding Gloydius intermedius and Scincella huanrenensis, are known appear in paddy wetlands which they use for foraging[29, 34, 62]. As a result, forests and agricultural land, which were the main habitats of herpetofauna species identified from a macroscopic point of view, adequately reflected the main habitats of herpetofauna species reported in previous studies. The most important habitats were paddy wetlands for amphibians and forests for reptiles[27, 31].
The geographic distributions of herpetofauna species predicted by species distribution modeling were consistent with the geographic ranges reported by previous surveys (Figs. S1, S2). According to previous studies, nine amphibian species are widely observed inland, while the other amphibian species are known to have a limited distribution range[24, 30, 33]. Onychodactylus fischeri, Bufo stejnegeri, and Rana huanrenensis are densely distributed in the northeastern regions, including Gangwon-do, Gyeonggi-do, and Gyeongsangbuk-do. Kaloula borealis, Rana plancyi, and Hyla suwonesis are found in central and western regions, including Chungcheongnam-do and Gyeonggi-do, while Karsenia koreana is found in the central regions of Chungcheongnam-do and Chungcheongbuk-do. Rana catesbeiana is found in southern regions, including Gyeongsangnam-do, Jeollanam-do, and Jeju-do, and Hynobius yangi is concentrated in Gyeongsangnam-do[26, 61, 62, 67]. Regarding reptiles, 13 species are widely observed inland, while Scincella huanrenensis and Gloydius intermedius, are mainly distributed in northeastern regions such as Gangwon-do, Gyeonggi-do, and Gyeongsangbuk-do; Eremias argus in central and western regions such as Chungcheongnam-do and Gyeonggi-do; and Gekko japonicus, Sibynophis chinensis, Coluber spinalis, and Amphiesma vibakari ruthveni in southern regions such as Gyeongsangnam-do, Jeollanam-do, and Jeju-do[62, 68, 69].
In South Korea, recent studies have indicated the need for using habitat prediction models for the establishment of protected areas for wild animals and plants[5, 33, 70, 71]. Habitat prediction model studies can be used to provide objective and scientific methods and procedures for the establishment of protected areas[4, 6, 20]. Previous studies carried out with the aim of establishing habitat conservation areas for herpetofauna species in other regions have used habitat prediction models, for example to establish protected areas for 16 endangered species belonging to the family Hylidae in South America, and to determine which areas are in need of conservation for the protection of seven species belonging to the family Viperidae inhabiting northeast Africa[4, 72]. In addition, the hotspot areas for all herpetofauna species inhabiting Madagascar were identified through their distribution patterns, and more conservation areas were suggested in addition to national parks based on the hotspot areas of all herpetofauna species inhabiting Morocco[6]. In South Korea, the main distribution areas of seven endangered herpetofauna species have been found to be Chungcheong-do and western Gyeonggi-do, and the main distribution areas of three amphibian species of the genus Rana and three reptile species of the genus Gloydius have been found to be located around the Taebaek Mountains in Gangwon-do[7, 29, 30]. These areas were similar in location and extent to the hotspot areas identified in the present study, and were also included in national conservation areas such as national parks. Nevertheless, some modifications should be made and additional conservation areas should be established in consideration of the hotspot areas where many herpetofauna species have been observed.
In the present study, more hotspot areas for herpetofauna species were predicted to be located in Gangwon-do than in the other provinces (Fig. 4). In Gangwon-do, forests account for 81% of the total area, mostly because of the presence of the Taebaek Mountains. As Gangwon-do is the administrative district with the lowest population density, various ecological conservation areas designated by the government are located here[73, 74]. The national conservation areas in Gangwon-do, where many of the hotspot areas for herpetofauna species are located, included the Demilitarized Zone (DMZ) located in the northern region; the water resources conservation areas of Chuncheonho Lake, Paroho Lake, and Soyangho Lake located in the western region; and Seoraksan and Odaesan National Parks located in the eastern region (Fig. 5). In these areas, the ecosystem is not damaged, and high biodiversity is maintained as access by civilians has been restricted since the end of the Korean War in 1953[75, 76]. According to previous surveys conducted in the DMZ from 1989 to 2016, 16 amphibian and 18 reptile species were known to inhabit the area[77]. According to the habitat status data for each national park located in Gangwon-do obtained from studies conducted from 1997 to 2019, 11 amphibian and 12 reptile species were observed in Seoraksan Mountain; 12 amphibian species and 14 reptile species were observed in Odaesan Mountain; 12 amphibian species and 14 reptile species were observed in Chiaksan Mountain; and eight amphibian species and 10 reptile species in were observed Taebaeksan Mountain[78]. In the present study, some hotspot areas were located within the areas included in national parks, but a relatively low number of cells among the predicted hotspot areas were already included in the national conservation areas (Fig. 5). Except for the edge of the national park located around the Taebaek Mountains, it was predicted that most of the regions were not suitable for the habitation of various species as the altitudes were higher than 1,000 m. Previous studies focusing on national parks have also revealed that species diversity was low at altitudes above 1,000 m and that diverse species were identified in areas with low altitudes[25]. Therefore, although there were some overlapping areas between the national conservation areas and the hotspot areas predicted in the present study, the national conservation areas did not adequately reflect the overall areas where the protection of herpetofauna species was required.
In the present study, the hotspot areas for herpetofauna species were identified in various regions other than Gangwon-do. In particular, hotspot areas for amphibians were mostly concentrated in Chungcheongnam-do and its surrounding areas, and hotspot areas for reptiles were concentrated in the areas around the southwest coast and the areas of the four major rivers (Fig. 5). Chungcheongnam-do and its surrounding areas consist of plains with low altitudes. In this province, well-developed paddy wetlands are used by amphibians as the main feeding and breeding grounds. Unlike other regions, this province had high biodiversity, with dense populations of endangered amphibians such as Kaloula borealis, Rana plancyi, and Hyla suwonesis[7, 27]. In the areas around the southwest coast and the areas of the four major rivers (Hangang River, Geumgang River, Nakdonggang River, and Yeongsangang River), high biodiversity may have been identified because of the habitats of Eremias argus, Pelodiscus sinensis, Chinemys reevesii, and Trachemys scripta elegans, which mainly inhabit coastal sand dunes, revers, and streams, which are not present in other regions[7,62,79]. However, many of the hotspot areas for amphibians were not included in the national conservation areas.
The national conservation areas of South Korea included more than 30% of areas inhabited by seven to nine amphibian species and nine to 13 reptile species together, as well as some hotspot areas for herpetofauna species, playing an important role in habitat conservation. However, more hotspot areas were identified outside the national conservation areas. Therefore, we showed that habitat protection is not carried out in these hotspot areas not included in the national conservation areas, with a high risk of habitat destruction because of development such as road and apartment construction. Therefore, for the protection of herpetofauna species, it is necessary to establish new conservation areas with a focus on herpetofauna species after confirming the actual inhabitation of species through precise monitoring in the predicted hotspot areas. Furthermore, the hotspot areas where the actual habitats were identified need to be designated as protected areas with priority over other areas by restricting development, tree harvesting, and the inflow of farms. These results can serve as important basic data for establishing protection measures and designating protected areas for herpetofauna species.
As a result of comprehensive analysis of the hotspot areas of 39 herpetofauna species, Gangwon-do was identified as the province with the highest number of hotspot areas, predicted to be inhabited by 10 to 12 amphibian species and 13 to 16 reptile species. In addition, amphibians were predicted to be concentrated in paddy wetlands around Chungcheongnam-do, and reptiles in the areas around the southwestern coast and areas of the four major rivers. Some hotspot areas were included within the national conservation areas, but many hotspot areas were located in areas not designated as conservation areas. It is necessary to protect the habitats of herpetofauna species by expanding the conservation areas after verification through detailed surveys in these areas. In the future, if the exact distribution range of Dryophytes flaviventris, which is a new species recently discovered and has not been included in this study, is revealed, more hotspot areas in addition to those revealed in this study may be discovered.