S-Space College of Natural Sciences (자연과학대학) Dept. of Biological Sciences (생명과학부) Theses (Ph.D. / Sc.D._생명과학부)
Why are anurans threatened? The case of Dryophytes suweonensis
왜 무미양서류는 멸종위기에 처해 있는가? 수원 청개구리의 사례를 통하여
- Amaël Borzée
- Jablonski P.
- 자연과학대학 생명과학부
- Issue Date
- 서울대학교 대학원
- endangered species; anthropogenic pressure; anuran; Dryophytes treefrog; threat; conservation
- 학위논문 (박사)-- 서울대학교 대학원 : 자연과학대학 생명과학부, 2018. 2. Jablonski P..
- The sixth mass extinction is under way, and amphibians are leading the race. An unpredictably high number of amphibian species is under threats of extinction. Factors of population decline in amphibians include (1) habitat destruction, (2) agrochemical and chemical pollution, (3) UV-B radiation, (4) diseases, (5) introduced species, (6) exploitation, (7) climate change and (8) complex causes, being the combined effects of the factors above. For any given species, some factors are of major significance, while other may be considered negligible. The loss of habitat due to urban development and encroachment is a major threat to almost all endangered species. Since the Neolithic Agricultural Revolution, humans have largely settled in lowlands, the primary breeding habitats for the majority of amphibian species. This trend continues nowadays, culminating in metropoles around the world. Encroachment also results in decreased connectivity between metapopulations, and is linked to the resulting genetic depression. Anthropogenic modification of landscapes also impacts the behaviour and ecology of species, leading to new competition dynamics. For instance, agricultural practices and the loss of natural habitat bring geographically isolated species in contact, potentially leading to introgressive extinction. Finally, the use of chemicals and their presence in the environment, and the introduction of invasive species are factors that can bring a last blow to already weak and destabilised species.
My dissertation aims at assessing the status of the endangered Suweon Treefrog, Dryophytes suweonensis, to ultimately predict the species probability of survival. The species is present on a narrow range on west Korean lowlands, and completes its life cycle in rice paddies. It co-occurs with the widespread Japanese treefrog (D. japonicus), with which it interacts on a broad spectrum. The first step of this dissertation was to estimate the entire distribution of D. suweonensis in the Republic of Korea. With the data on its distribution and population size, I estimate the meta-population connectivity of the species, and the relationship between range size and fitness depression. I then assess competition, diet overlap and habitat segregation with D. japonicus. Because of the spatial arrangement and anthropogenically modified breeding strategy of the two treefrog species in rice paddies, I investigated hybridization between D. suweonensis and D. japonicus and the possibility of introgressive extinction in D. suweonensis. Besides, I investigated the phylogenetic relation between D. suweonensis and other closely related Hylid species in North East Asia to clarify recent evolutionary history. I then assessed the threats linked to the winter ecology of the species, and to chemical run-off resulting from agricultural practices. Finally, I assessed the potential for translocation and reintroduction of the species through a pilot study. I established long term population trends, before running a Population Viability Analysis to assess the probability of extinction for D. suweonensis.
This research project is organised under five main parts: (I) demography, (II) behavioural ecology, (III) phylogenetics, and (IV) other factors of population decline and conservation assessment. This dissertation has two intrinsically connected principal aims. First, I determine the threatened status of D. suweonensis, in relation to habitat, ecology, competition and disease, and provide possible solutions for its conservation. The second aims is on a broader scale, intending to demonstrate the impact of landscape anthropisation on metapopulation connectivity, exemplify the need for long term surveys to estimate fluctuating population sizes, demonstrate the impact of range restriction on behavioural fitness, retrace evolutionary history through current behavioural patterns, demonstrate the risks of introgressive extinction, highlight the role of resurgence in the Yellow Sea for speciation events, and finally, demonstrate the relationship between healthy invasive carriers and emergent anuran pathogens. Each of the 14 chapters is linked to the endangered status of D. suweonensis, and all highlight a different type of threat that has the potential to accelerate the decline of the species, to the point that it could be extinct within a short period.