This species is known with certainty only between 1,000–2,000 m Asl on the Langbian Plateau in the southern reaches of the Vietnamese Central Highlands (Smith 1923, Poyarkov et al. 2014). There are reports of the species from southeastern Thailand through the Cardamom Mountains of Cambodia to central Viet Nam and Lao PDR (Taylor 1962, Inger et al. 1999, Stuart 1999, Ohler et al. 2002), however the Lao PDR records have since been attributed to other species and other populations outside the Langbian Plateau are unlikely conspecific with M. annamensis (Poyarkov et al. 2014). Such populations are herein excluded, however further taxonomic studies are needed to confirm the species' absence from these localities. The species' EOO is 9,889 km2, which represents five threat-defined locations.
Habitat and Ecology
This species occurs in montane evergreen mixed forest and has mostly been observed on the forest floor (Poyarkov et al. 2014). Within the Langbian Plateau, breeding has been observed on Bidoup Mountain during July and on Chu Pan Phan Mountain during March and April (Poyarkov et al. 2014). Breeding occurs after heavy rains, when calling males, gravid females and amplexing pairs have been observed adjacent to forest streams (Poyarkov et al. 2014). The species' tadpoles develop in temporary pools or slow-flowing stream sections (Poyarkov et al. 2014).
Very little is known about the size of this species' population and it has been detected in few surveys (Smith 1923, Poyarkov et al. 2014). Further surveys are needed to determine its population size and trends. It is likely that ongoing forest loss associated with expanding agriculture throughout Southeast Asia (Meyfroidt and Lambin 2008, Sodhi et al. 2009, Meyfroidt et al. 2013) is causing some populations declines.
Habitat loss and degradation due to rapidly expanding agriculture is an ongoing threat to biodiversity throughout Southeast Asia (Sodhi et al. 2009). In the Central Highlands of Viet Nam large areas of forest are converted to agricultural land to grow cash crop plantations (e.g. rubber, coffee and tea) (Meyfroidt and Lambin 2008, Meyfroidt et al. 2013), and recent satellite imagery shows areas of land cleared for agriculture throughout the species' predicted range.
This species is known from Bidoup-Nui Ba and Chu Yang Sin National Parks (Poyarkov et al. 2014). Phuoc Binh Proposed Nature Reserve, Rung Thong Da Lat Cultural and Historical site, and several other protected areas are included in its predicted range; the species likely occurs in some of these also. Increased protection of some of the protected areas from which the species is known may be warranted to mitigate declines.
Addressing the lack of data is the first step towards ensuring this species' long-term persistence; further research on its true distribution, threats, and the size and trends of its population would inform conservation decisions.
Red List Status
Listed as Vulnerable as this species has an extent of occurrence (EOO) of only 9,889 km2, is expected from five threat-defined locations, and is facing a continuing decline in the quality of parts of its habitat.
Some Vietnamese specimens previously referred to M. annamensis have recently been described as a separate species, M. marmorata (Bain and Nguyen 2004), and the Ha Tinh, Thai, and Cambodian specimens should be compared to M. annamensis, M. pulverata, and M. marmorata for confirmation of identity.
IUCN SSC Amphibian Specialist Group 2017. Microhyla annamensis. The IUCN Red List of Threatened Species 2017: e.T57874A55069709. http://dx.doi.org/10.2305/IUCN.UK.2017-2.RLTS.T57874A55069709.en .Downloaded on 21 January 2019