Taxonomy and ecology of amphibian communities in Southern Vietnam

Abstract

The Langbian Plateau is known as the southernmost extension of the Truong Son Range (or Annamite Mountains) in southern Vietnam. This area is the type locality of many amphibian species: six species described by Smith (1924) and another species, Microhyla fusca, discovered by Anderson (1942). In terms of species richness, Bourret (1942) recorded 19 species of amphibians from this plateau and the species number was increased to 67 in the most recent checklist of Nguyen et al. (2009). However, the knowledge about the amphibian fauna of the Langbian Plateau is still imperfect, in particular the species complexes and their natural history.<br /> In this study, I focus on the taxonomy and ecology of the amphibian community of the Langbian Plateau by using morphological and bioacoustic approaches. Specific objectives of this study are: (1) to assess the species richness of the amphibian fauna, (2) to investigate the community structure of amphibians, (3) to evaluate biogeographic relationships of the amphibian faunas between the Langbian Plateau and adjacent areas, (4) to analyze advertisement calls of anurans, and (5) to determine the major threats to the amphibian fauna of the Langbian Plateau.<br /> A total of 15 field surveys were conducted in Bidoup - Nui Ba National Park, Chu Yang Sin National Park, Phuoc Binh National Park, Ta Dung Natural Reserve, and Song Luy - Song Mao watershed forests during three years 2010−2012. The surveys were conducted in different forest types, including cloud forest, evergreen forest, mixed forest composed of hardwoods and bamboo, mixed forest composed of small hardwoods and bamboo, and cultivated area in buffer zone, at elevation range from 200 m to ca. 2000 m.<br /> Resulting from this study, a collection of 651 specimens was used for morphological examination and 59 call records were made for bioacoustic analyzing. A total of 44 amphibians, belonging to 23 genera, six families were recorded from the Langbian Plateau. We also provided a number of new provincial records of amphibians in southern Vietnam, comprising four species from Dak Lak Province, 21 species from Dak Nong Province, seven species from Lam Dong Province, 13 species from Ninh Thuan Province, and 14 species from Binh Thuan Province. Remarkably, three new species were recently discovered from the Langbian Plateau by our group working, namely Leptobrachium pullum, Leptolalax bidoupensis, and Rhacophorus vampyrus. <br /> In the first part of the results of this dissertation, a list and species descriptions of all recorded species were presented in detail. Moreover, additional information about reproductive biology of 15 species, comprising of three species of Megophryidae, one species of Microhylidae, two species of Ranidae and five species of Rhacophoridae, was also provided.<br /> The distribution pattern of amphibian species from the Langbian Plateau was presented in the second part. In terms of geographic distribution, 30 amphibian species were recorded from Bidoup - Nui Ba National Park, 18 from Chu Yang Sin National Park, 20 from Phuoc Binh National Park, 25 from Ta Dung Natural Reserve, and 18 from Song Luy Song Mao watershed forest. Among 44 recorded anurans, nine species were found in cloud forests, 32 species in evergreen forests, 21 species in mixed forests composed of hardwoods and bamboo, 18 species in mixed forests composed of small hardwoods and bamboo, and 11 species in cultivated areas. Although the anuran fauna of the cloud forests is not diverse, it contains most of the endemic species. Six of nine species found in the cloud forests are restricted to Indochina. The species composition of the cloud forests is more similar to that of the evergreen forests than to those of other forest types. The anuran fauna of the evegreen forests is more similar to that of the mixed forests composed of hardwoods and bamboo than to that of the cultivated areas. <br /> In terms of altitudinal distribution, the highest species richness is known at elevations around 1500 m. The diversity decreases at elevations below 900 m and above 1800 m. The CCA biplot for the communities at different elevations showed the overlap in species composition among the ranges of elevations from 600 to 1800 m with the 95% confidence ellipses, estimated for each range of elevations. With respect to the life-mode segregation, the more distance is away from the water bodies, the less number of amphibian species is found. In Langbian Plateau, we recorded 27 aquatic species, 28 terrestrial species and 28 arboreal species. The species number of amphibians decreases at higher elevations because the forests on mountain tops harbor more terrestrial and arboreal species but fewer aquatic species than the forests at lower elevations.<br /> The third part of the results mentioned about the biogeographic relationships. The cluster analyses indicated that the amphibian fauna of the eastern hill of Cambodia, a western extended part of the Langbian Plateau, intensively overlapped with that of the Song Luy Song Mao watershed forest. The amphibian fauna of the Langbian Plateau is more similar to that of the Kon tum Plateau than to that of the Cardamom Mountains. <br /> In the fourth part of the results, advertisement calls of 13 anuran species from the Langbian Plateau were described (Megophryidae: 5, Ranidae: 3, and Rhacophoridae: 5). The call descriptions of five Indochina endemic species, listed in the IUCN Red List as vulnerable or nearly threatened (Brachytarsophrys intermedia - VU, Hylarana attigua - VU, Kurixalus baliogaster - VU, Rhacophorus annamensis - VU, and R. calcaneus - NT), were introduced for the first time. It is also the first time that the advertisement call of Hylarana milleti has been described.<br /> Many anurans showed the behavior of forming chorus congregations, six of 13 species that have advertisement calls described here gave proofs of calling in choruses. Intraspecific chorus behaviors of three species were interpreted (Leptobrachium pullum, Leptolalax bidoupensis, and Hylarana milleti). Proofs of interspecific chorus behaviors of anurans in the Langbian Plateau were also provided.<br /> In the discussion part, taxonomic problems of the morphologically similar species or species complexes are mentioned. Based on specimen examination several taxa are likely species complexes (e.g., Hylarana nigrovittata, Polypedates leucomystax, Brachytarsophrys intermedia, Raorchestes gryllus, Rhacophorus calcaneus and R. robertingeri). <br /> Another aim of this study is linking the morphology and bioacoustics to support for taxonomic identification. Therefore, I compared the advertisement call of morphologically similar species of the families Megophryidae, Ranidae and Rhacophoridae (e.g., among the populations of Hylarana nigrovittata complex or between H. attigua and H. milleti). <br /> Regarding the biogeographic relationships, our cluster analyses supported the results of Bain and Hurley (2011) that the amphibian fauna of the Cardamom Mountains is closely related to that of the Kon Tum Plateau. <br /> Finally, conservation potential and threats to the amphibians of the Langbian Plateau were also evaluated. On the one hand, the amphibian fauna of the Langbian Plateau has a high conservation potential because of a high level of species diversity with 44 recorded species and a large number of endemic/threatened species. A total of 14 species are endemic to Indochina, two species are restricted to the subregion Southern Annamites, and six species are currently known only from the Langbian Plateau. Nine species are listed in the IUCN Red List (2012) as globally threatened species (six species as vulnerable and three species as nearly threatened). On the other hand, the amphibian species in the Langbian Plateau are facing a decline because of habitat loss and fragmentation.<br /> Based on these results, further research that focuses on the following fields is recommended: (1) taxonomic and distributional status of the amphibians in the Langbian Plateau; (2) calling behavior in anurans in the Langbian Plateau and adjacent areas; and (3) more conservation work for restoring forests or linking isolated forests, and pollution controll management in the Langbian Plateau.