Ecology and Conservation of the Laotian langur Trachypithecus laotum in a Protected Area of Laos (Southeast Asia)

Abstract

Terrestrial species from the Lao People’s Democratic Republic (PDR) are under high threat due to deforestation and overhunting. Previous studies have even defined these forests as subjected to an “empty forest syndrome”, a condition in which forests that are apparently well preserved are instead almost deprived of vertebrate faunas due to extreme exploitation by local communities. Forest specialists, including several primates, are among the most threatened species in the country. The Laotian langur (Trachypithecus laotum) is endemic to Lao PDR, is listed as Endangered by the IUCN Red List, and it is one of the least studied species in the region. A survey on the local distribution, life history and conservation status of the Laotian langur was carried out in Phou Hin Poun National Protected Area, Khammouane Province of Lao PDR. The survey consisted of an initial phase with interviews to select key informants on the Laotian langur and the other primate species of the area. Then, a phase of field surveys along forest transects, totaling 64.1 km of 21 transects, yielded a record of 35 individuals in 9 groups. The highest encounter/detection rate of the Laotian langur was 1 group per km at one sector of the park. In contrast, it was much lower (0.18–0.34 groups/km) in the rest of the protected area. The group sizes were much lower than those observed in the same area between 1994 and 2010, thus suggesting a decline in the population size of langurs. This decline may be linked to habitat loss (timber extraction and mining). Still, also overhunting, as signs of poaching were observed during our field surveys. This was also supported by the reports of our interviewees. Laotian langurs were observed to be sympatric and interact while foraging with the Assamese macaque (Macaca assamensis). In the cases of sympatric occurrence between the two species, we observed that subtle mechanisms of niche partitioning may occur to reduce interspecific competition for food. Further research on the population and ecology of this endangered langur should be conducted to understand the species and aid its conservation.

Population Status and Conservation of the Largest Population of the Endangered François’ Langur (Trachypithecus francoisi) in Vietnam

“…The mean group size, 8.21-9.06, of the François' langur in Lam Binh is comparable with those of other limestone langurs in Vietnam, e.g., 8.11 in the Hatinh langur [35] and 7.27 in the Delacour's langur [8], but greater than the Laotian langur (Trachypithecus laotum) with mean group size of about 3.88 [36] and the Cat Ba langur (T. poliocephalus) of around 5.27 [37]. While group size in folivores is often determined by several factors, including their behaviors, ecological resources, and predation [38][39][40][41][42][43], they have been shown to differ between limestone and forest langurs, with forest populations usually being larger.…”

“…Based on the available data, it seems that the mean group size in the Lam Binh population is approaching the equilibrium in limestone langurs, even though poaching still takes place (see more information below). Nonetheless, it is most likely that the small group sizes in other langurs from Laos and Vietnam are attributable to historical and/or current hunting pressures [8,[34][35][36].…”