Modeling the Red-Shanked Douc (Pygathrix nemaeus) distribution in Vietnam using Maxent

VNU Journal of Science: Earth and Environmental Sciences, Vol. 35, No. 3 (2019) 61-71 
61 
Original Article 
Modeling the Red-shanked Douc 
(Pygathrix nemaeus) distribution in Vietnam using Maxent 
Nguyen Tuan Anh1, Le Duc Minh1,2, , Pham Viet Hung2, Vu Thi Duyen1 
1Faculty of Environmental Sciences, VNU University of Science, 334 Nguyen Trai, Hanoi, Vietnam 
2VNU Central Institute for Natural Resources and Environmental Studies, 
19 Le Thanh Tong, Hanoi, Vietnam 
Received 9 May 2019 
Revised 12 July 2019; Accepted 9 August 2019 
Abstract: The Red-shanked Douc (Pygathrix nemaeus) is the only douc species recorded in all three 
countries of Indochina. It is classified as Endangered by IUCN, and is believed to have experienced 
a major drop of more than 50% of its population over the last 40 years. The known distribution of 
main P. nemaeus populations in Vietnam ranges from Pu Mat National Park, Nghe An Province in 
the North to the Kon Ha Nung, Gia Lai Province in the South. In this study, we used Maxent, a 
species distribution modeling approach that is shown to a have high predictive power even with low 
number of occurrence records, to predict the current distribution of the Red-shanked Douc in 
Vietnam based on published records. The results show that P. nemaeus inhabits a region from Nghe 
An to Kon Tum Province, with areas from Ha Tinh, Quang Binh, Quang Tri, Thua Thien – Hue, Da 
Nang – Quang Nam Provinces exhibiting the highest potential. With all model parameters already 
listed here, studies in the future may incorporate more occurrence records to develop better models, 
or other environmental variables to assess the influence of different factors on the species 
distribution. The results also suggest that species distribution modeling, coupled with a carefully 
checked and filtered occurrence dataset, as well as species-specific model fine-tuning and 
evaluating, can help address many conservation issues in Vietnam. 
Keywords: Maxent, Red-shanked Douc, Species Distribution Modeling. 
________ 
 Corresponding author. 
 E-mail address: le.duc.minh@hus.edu.vn 
 https://doi.org/10.25073/2588-1094/vnuees.4390 
N.T. Anh et al. / VNU Journal of Science: Earth and Environmental Sciences, Vol. 35, No. 3 (2019) 61-71 
62 
1. Introduction 
Doucs (genus Pygathrix) are members of the 
Old World monkey subfamily Colobinae [1]. 
This genus contains three species: The Red-
shanked Douc (P. nemaeus), Grey-shanked 
Douc (P. cinerea), and Black-shanked Douc (P. 
nigripes). The doucs are found only in Indochina 
and all have limited geographic ranges, and have 
been threatened with the shrinking of forested 
habitat areas in their natural distributions [2]. 
The Red-shanked Douc is only douc species 
recorded in all three countries of Indochina. The 
core populations of the Red-shanked Douc now 
reside in Vietnam and Laos, and it was recently 
confirmed for northern Cambodia through a 
genetic analysis [3]. The extent of the species 
distribution in Cambodia is, however, still in 
question, and it is likely to be considerably 
restricted. The douc individuals from Cambodia 
share many characteristics with those from 
southernmost Laos [3–5]. The distribution of 
Pygathrix nemaeus in Vietnam ranges from Pu 
Mat National Park, Nghe An Province in the 
North (19°02’N) to the Kon Ha Nung area, Gia 
Lai Province in the South (14°33’N) [6]. 
The Red-shanked Douc occurs mainly in 
evergreen and semi-evergreen forests, and is 
sometimes associated with limestone forest, but 
this association is still in question. It is diurnal 
and arboreal, and was recorded at an elevation 
up to 1,600 m. The doucs are highly folivorous, 
with around 75% of their diet consisting of 
leaves, and sometimes buds, fruit, seeds, and 
flowers [5–7]. Behavioral characteristics of this 
species make it an easy target for hunting, and 
recent field observations have suggested that the 
group size may vary considerably as a possible 
consequence of environmental and human 
disturbances [8–10]. 
It is classified as Endangered by IUCN [7], 
and is believed to have experienced a major 
decline of more than 50% of its population over 
the last 40 years due to a combination of war 
effects, habitat loss, and illegal hunting [7, 11]. 
The Red-shanked Douc is listed as 
“Endangered” in the Red Data Book of Vietnam 
(Ministry of Science, Technology, and 
Environment 2007). This species is also listed in 
Appendix I of the Convention on International 
Trade in Endangered Species of Wild Fauna and 
Flora (CITES). Hunting is currently the main 
threat to the Red-shanked Douc, mostly for 
subsistence use and traditional medicine 
[4,6,12]. Destruction of its natural habitat is the 
second major threat to this species, as many 
areas in central Vietnam have been cleared and 
shifted to anthropogenic land uses due to the 
rapid growth of Vietnam population since the 
post war period [6]. As often the case with 
endangered species, laws and regulations created 
to protect them are difficult to enforce – even 
though the country has granted the Red-shanked 
Douc the highest protection status. 
Background on Species Distribution Modeling 
(SDM) 
SDM is a relatively new approach that is 
useful in studying biogeography and 
evolutionary ecology. It can be used to assess the 
suitability of distribution range for a taxon, and 
is become a common approach employed to 
address conservation issues [13-16]. In general, 
SDMs use the relationship between observed 
points of occurrence and influencing variables 
(termed “environmental variables) to generate a 
probability map rating the suitability for a 
species of a given area. SDMs can help to locate 
areas climatically suitable for a species but have 
not yet been discovered [13, 17]; to identify 
cryptic species lineages whose other traits such 
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