Impact of land reclamation and agricultural water regime on the distribution and conservation status of the endangeredDryophytes suweonensis

Abstract

Knowledge about the distribution and habitat preferences of a species is critical for its conservation. The Suweon Treefrog (Dryophytes suweonensis) is an endangered species endemic to the Republic of Korea. We conducted surveys from 2014 to 2016 at 890 potentially suitable sites across the entire range of the species in South Korea. We then assessed whether D. suweonensis was found in the current and ancestral predicted ranges, reclaimed and protected areas, and how the presence of agricultural floodwater affected its occurrence. Our results describe a 120 km increase in the southernmost known distribution of the species, and the absence of the species at lower latitudes. We then demonstrate a putative constriction on the species ancestral range due to urban encroachment, and provide evidence for a significant increase in its coastal range due to the colonisation of reclaimed land by the species. In addition, we demonstrate that D. suweonensis is present in rice fields that are flooded with water originating from rivers as opposed to being present in rice fields that are irrigated from underground water. Finally, the non-overlap of protected areas and the occurrence of the species shows that only the edge of a single site where D. suweonensis occurs is legally protected. Based on our results and the literature, we suggest the design of a site fitting all the ecological requirements of the species, and suggest the use of such sites to prevent further erosion in the range of D. suweonensis.

Policy Recommendation for the Conservation of the Suweon Treefrog (Dryophytes suweonensis) in the Republic of Korea

“…The transformation of rice paddies into natural wetlands is not recommended at the moment as the data available on the natural requirements of the species are still limited and transformations may result in the local extirpation of the species if conducted inadequately. The knowledge currently available only includes partial vegetation data, habitat size, and distribution models (Borzée and Jang, 2015;Song, 2015;Borzée et al, 2017a). In this regard, we recommend the implementation of protected area at the sites of Sihung, Iksan, Paju, Asan, and Chungju based on genetic variability (Borzée et al, 2018c; Figure 1), large source populations, buffer populations and important populations for connectivity (Borzée, 2018).…”

“…We recommend the ban of pesticides and herbicides in the rice-paddy complexes where D. suweonensis is known to occur (Borzée et al, 2017a; Figure 1), as these are related to lower population sizes (Borzée et al, 2018d). The chemicals to be avoided are the ones resulting in high levels of phosphates and nitrates in the environment, and their application should be avoided during the breeding season (May and June) and tadpole development (June and July).…”

“…The Suweon Treefrog (Dryophytes [Hyla] suweonensis; Duellman et al, 2016) is an endangered species in the Republic of Korea (IUCN, 2018) due to a low extent of occurrence (Borzée et al, 2017a), fragmented population (Borzée, 2018) and continuing decline in area of occurrence . About 2,500 calling males are estimated to be present in the Republic of Korea , segregated into 14 disconnected areas (Borzée, 2018).…”

“…In the Republic of Korea the species ranges from the Mangyeong River in the south to the Imjin River in the north (Kim et al, 2012;Borzée et al, 2016cBorzée et al, , 2017a. Population sizes are generally decreasing because of habitat loss through encroachment and urbanization (Lee and Miller-Rushing, 2014), although some rare populations displayed low increases between 2015 and 2017 .…”

“…It is important to protect the species due to its clear evolutionary potential, differentiated from other Hylid species by a switch in heterogamety resulting in a ZW system (Dufresnes et al, 2015), and in regard to the international conservation crisis involving amphibians worldwide (Stuart et al, 2004;Beebee and Griffiths, 2005;Bishop et al, 2012;Wake, 2012;Howard and Bickford, 2014;Pimm et al, 2014). Despite the current situation, D. suweonensis is not present in any protected area (Borzée et al, 2017a) and is only known to breed in rice paddies (Borzée and Jang, 2015), while original potential habitats might have included wetlands with low vegetation including Alopecurus sp. and Typha spp.…”