Journal of Threatened Taxa |
www.threatenedtaxa.org | 26 June 2021 | 13(7): 18679–18686
ISSN 0974-7907 (Online) | ISSN 0974-7893
(Print)
https://doi.org/10.11609/jott.7273.13.7.18679-18686
#7273 | Received 07 April 2021 | Final
received 05 June 2021 | Finally accepted 09 June 2021
Persistence of Trachypithecus geei (Mammalia:
Primates: Cercopithecidae) in a rubber plantation in
Assam, India
Joydeep Shil
1, Jihosuo Biswas 2, Sudipta Nag 3 &
Honnavalli N. Kumara 4
1,4 Sálim Ali Centre for Ornithology and
Natural History (SACON), Anaikatty P.O., Coimbatore,
Tamil Nadu 641108, India.
1 Manipal Academy of Higher
Education, Madhav Nagar, Manipal, Karnataka 576104, India.
1–3 Primate Research Centre Northeast
India, House No. 4, By lane 3, Ananda Nagar, Pandu Port Road, Guwahati, Assam
781012, India.
3 Department of Zoology, School of
Biological Sciences, University of Science & Technology Meghalaya, Techno
City, Killing Road, Baridua 9th Mile, Meghalaya
793101, India.
1 joydshil@gmail.com, 2 jihosuo@yahoo.com,
3 sudiptanag74@gmail.com, 4 honnavallik@gmail.com
(corresponding author)
Editor: Andie
Ang, Mandai Nature, Singapore. Date
of publication: 26 June 2021 (online & print)
Citation: Shil, J., J. Biswas, S. Nag
& H.N. Kumara (2021). Persistence
of Trachypithecus geei in a
rubber plantation in Assam, India. Journal of Threatened Taxa 13(7): 18679–18686. https://doi.org/10.11609/jott.7273.13.7.18679-18686
Copyright: © Shil et al. 2021. Creative Commons Attribution 4.0
International License. JoTT allows unrestricted use, reproduction, and
distribution of this article in any medium by providing adequate credit to the
author(s) and the source of publication.
Funding: This study was partially funded by Department of Science and Technology, Govt. of India (SERB Grant No. SR/SO/ AS -
17/2012); Wildlife Trust of India; Primate Conservation Inc.
Competing interests: The authors declare no competing interests.
Author details: Joydeep Shil—research scholar in SACON,
and researcher at Primate Research Centre Northeast India. His interest lies in
study of mammals especially primates in northeastern India. Jihosuo Biswas—heads
the ‘Primate Research Centre Northeast India’. His studies focus on ecology, behaviour and conservation of primates of northeastern
India.
Sudipta Nag—was a researcher at Primate
Research Centre northeast India and currently working as an assistant
professor in the Zoology department of University of Science and Technology,
Meghalaya. Honnavalli N. Kumara—wildlife biologist in
SACON. His interest lies in study of mammals with special emphasis on primates
in India.
Author contributions:
JS—conceptualisation of the study, data
collection-compilation-analysis, and writing of the manuscript; JB—data
collection, conceptualisation, executing the study
and fundraising; SN—data collection; HNK—guiding the data compilation-analysis,
writing manuscript.
Acknowledgements: We are thankful to the Department
of Environment and Forest, Government of Assam particularly PCCF (Wildlife) Mr.
S. Chand and Mr. R.P. Agarwala, Council Head of the
Department, Forest, BTC Mr. A. Sargiary and others
for providing necessary permission and logistic support. We thank Mr. Richard
Taro, Mr. Dharmeswar Rabha, Mr. Pankaj Kumar Mili, Mr. Pritam Sarkar and Mr. Shah Nawaz Jelil for their support in the field. This study was
partially funded by Department of Science and Technology, Govt. of India (SERB
Grant No. SR/SO/AS-17/2012), Primate Conservation Inc. and Wildlife Trust of
India. All research protocols reported in this manuscript were reviewed and
approved by Salim Ali Centre for Ornithology and Natural History and Primate
Research Centre. The research complied with protocols approved by the
appropriate Institutional Animal Care Committee (Chief Wildlife Warden, Assam,
O.O. No: 336 dtd. 06.03.2013). The research adhered
to the legal requirements of the country in which the research was conducted.
Abstract: Non-human primates are highly
threatened as a result of habitat destruction, agricultural expansion,
industrial development, large-scale build-ups and wildlife trafficking. Nearly
60% of all primates are threatened and many are found in habitats with some form
of human modifications (e.g., croplands and plantations). The adaptability of
primates to survive in human-modified habitats is thus a key to determine their
persistence in anthropogenic landscapes. In this study, we examined the
population number and age-sex composition of the ‘Endangered’ Golden Langur Trachypithecus geei
in a rubber plantation in the Kokrajhar District in
Assam, India in 2016, and compared with past data of the langur population and
demographics from the same location to better understand the population
dynamics, demographic characters and persistence of the Golden Langurs in the
rubber plantation. In 2016, we recorded six groups of Golden Langurs totaling 78 individuals with a mean group size of
13.00±4.00SD. Of the total population, 10.29% were adult males,
41.18% were adult females, 32.35% were juveniles and 16.18% were infants. The
overall population growth from 1997 to 2016 was estimated to be 5.54% per year.
Habitat matrices of rubber plantations with natural forest patches are important
in the fragmented landscape for the persistence of Golden Langur populations.
They may also act as a corridor for the langurs to move between the fragments
and as food resources, highlighting the importance of such matrices for the
langurs outside protected areas. Population monitoring and ecological studies
in such matrices would therefore be needed for the successful implementation of
targeted management strategies for the conservation of these threatened
langurs.
Keywords: Anthropogenic landscape,
landscape supplementation, matrix, persistence, primate.
INTRODUCTION
Forest loss and habitat
degradation that is primarily driven by agricultural expansion and
intensification (Gibbs et al. 2010; Foley et al. 2011), are the major threats
to biodiversity (Maxwell et al. 2016). This anthropogenic modification of
ecosystems is globally widespread, resulting in many primate species living in
human-modified landscapes (Cowlishaw 1999; Cowlishaw & Dunbar 2000; Chapman & Peres 2001) with
remnant patches of natural vegetation (Prevedello
& Vieira 2010; Watling et al. 2011). Non-human
primates are most affected by anthropogenic habitat disturbance, partly due to
their high dependence on tropical forest ecosystems (Isaac & Cowlishaw 2004). Nearly 60% of the world’s primate species
distributed in the Neotropics, mainland Africa,
Madagascar, and Asia are threatened with extinction as a result of habitat
destruction, agricultural expansion, industrial development, large-scale
build-ups and wildlife trafficking (Estrada et al. 2017). In many parts of
Asia, lowland dry evergreen and semi-evergreen forest and dry deciduous forests
have been converted to plantations such as rubber and oil palm plantations
(McKenney et al. 2004; Tordoff et al. 2005). The adaptability of primates to
survive in human-modified habitats is a key to determine their persistence in
anthropogenic landscapes (Ferreira et al. 2018). While some primates are known
to use part of human-altered land covers (Pielke Sr.
et al. 2004; Davey 2006; Wickham et al. 2012), others use degraded habitats and
persist (e.g., Capped Langur Trachypithecus
pileatus: Borah et al. 2021). But the lack of
information on their ecological traits to utilize human-modified habitats
greatly limits our ability to implement targeted landscape management
strategies for their conservation.
Golden Langur Trachypithecus
geei (Khajuria, 1956)
is ‘Endangered’ (IUCN Red List; Das et al. 2020) and endemic to parts of Bhutan
and the Indian state of Assam (Wangchuk 1997; Choudhury 2002). In India, the
natural habitat of Golden Langur is primarily semi-evergreen and moist
deciduous forests (Champion & Seth 1968; Bahuguna
et al. 2016). A large part of the habitat of the Indian population of Golden
Langurs has been lost in the last three decades and the population has been
threatened (Srivastava 2006a). Several populations are confined to isolated
forest fragments (Srivastava et al. 2001a; Choudhury 2002; Srivastava 2006b).
Large-scale built-up areas and anthropogenic land-use patterns have changed the
landscape and divided the Golden Langur population in India into two parts,
viz., the northern and southern populations without contiguous habitats between
them (Srivastava et al. 2001b). The northern population has a vast pristine
area in Ripu Reserved Forest, Chirang
Reserved Forest, and Manas National Park (>500 km2)
and is connected to the langur population in Bhutan. On the other hand, the
southern population is confined to small habitat fragments (<50 km2)
with one subpopulation inhabiting a Rubber Hevea
brasiliensis plantation in Nayekgaon
in the Kokrajhar District in Assam, India. This
rubber plantation and its fringe forests were once connected with the Chakrashila Wildlife Sanctuary, which is still a natural
and protected habitat of the southern population of Golden Langurs. Over the
course of time, the area lost its continuity with the Chakrashila
Wildlife Sanctuary due to human settlement in adjacent forest areas (Medhi et al. 2004). In this study, we examined the
population number and age-sex composition of Golden Langurs in the rubber
plantation and surrounding areas in Nayekgaon in
2016, and compared with past data of the population and demographics from the
same location so as to assess population trend and persistence of the Golden
Langur in a small and isolated human-modified landscape. Previous studies were conducted
in 1997 (Srivastava et al. 2001a), 2002 (Medhi et al.
2004), and 2008 (Ghosh et al. 2009) but detailed information was not available
for the years 1997 and 2008 and hence we could only compare in detail with the
2002 data. Understanding the survival possibilities of such a population
outside their natural habitat would help in primate conservation and habitat
management.
METHODS
Study Area
The rubber plantation and its
surrounding plantation areas consist of approximately 277 ha and is situated
between 26.350–26.374 0N and 90.372–90.393 0E in Nayekgaon Village of the Kokrajhar
District, Assam, India. The rubber plantations started in 1985 and Golden
Langurs were also reported at the same time which indicated that the area was
once the natural habitat of Golden Langurs (Medhi et
al. 2004). The area is a private rubber plantation and comprises of 80% rubber
plantation and 20% natural forests with human settlements and roads (Medhi et al. 2004). Shorea
robusta, Tectona grandis, Bauhinia purpurea,
Bauhinia variegata, Mangifera
indica, Dillenia pentagyna, Duabanga grandiflora, Litsea glutinosa, Terminalia bellirica, Premna bengalensis, Albizia procera, Stereospermum personatum, and Ficus spp.
are the main species within the natural vegetation (Medhi
et al. 2004). During our study, we also recorded roughly 20% of the area
consisting of natural forests. Our interaction with the plantation manager
confirms that there was no further expansion of rubber plantation after 1985.
Climatic conditions of the area are humid with moderate temperature with high
rainfall during monsoon and dry with low temperature during winter (Barthakur 1986). The annual rainfall of the area is between
2,000 and 3,000 mm. Rhesus Macaques Macaca mulatta are sympatric with the langurs (Medhi et al. 2004). A study area map (Figure 1) was created
using QGIS 3.16.
Survey
Since the area of Nayekgaon rubber plantation is small, total count was
possible. We followed the same field protocol as the previous population
assessment in the same location in 1997 (Srivastava et al. 2001a, 2002; Medhi et al. 2004, 2008; Ghosh et al. 2009), i.e., block
count methods (Struhsaker 1975; Burnham et al. 1980;
NRC 1981) for a total count of the population. The area was demarcated into two
blocks by taking the road as a landmark (Figure 1). The road passes from east
to west through the rubber plantation and divides the area almost equally. Each
block was further divided into sub-blocks of 12 to 15 ha. Prior to the survey,
a one-day training workshop was conducted for the recording of geo-coordinates
and population assessment including age-sex of the individuals of Golden
Langurs. The teams were led by a trained biologist who was able to
differentiate the age and sex of individuals of Golden Langurs. The assessment
was conducted by 12 teams consisting of two people in each team. Each sub-block
was surveyed by a team of two people either in the morning or in the evening.
All the teams walked in parallel maintaining at least 200 m distance between
each team from 0600 to 1100 h and from 1400 to 1700 h on three consecutive days
from 26 to 28 February 2016. Each team was provided with a handheld GPS (Garmin
78S), 8×4 binocular, digital camera and Motorola wireless handset for
communication to avoid duplication in counting. When langurs were encountered,
we recorded the geo-coordinates of the location of the group, and observed the
group for sufficient time or until we could record the total number, and
age-sex of all the individuals in the group. The data on age and sex were
considered as adult male (AM), adult female (AF), juvenile (JU), and infant
(IN). Visibility was high in the rubber
plantation so there were no difficulties in locating the animals. The langurs
were habituated to human presence since they regularly came into contact with
plantation workers and researchers.
Data analysis
The groups were differentiated
and identified using the time, location, and group composition of adjacent
groups. Since the area was small, we adapted the total count method, and the
sum of the number of individuals in each identified group was considered as the
number of individuals in the study area. We calculated the density as a total
number of individuals in the total area.
The data of adult males and adult
females were combined to represent adults (AD) and the same was done for infant
and juvenile, represented as immature (IM), to compute the age-sex ratios. We
calculated the mean group size, mean individual of different age-sex
classification, and age-sex ratios using the data of all the groups. We could
not identify the age and sex of four of the individuals in one of the groups,
thus that group was not considered in the calculation for the mean age-sex
compositions but was considered for the total count and mean group size. We
compared the data of 2002 and 2016 to check for any significant differences. We
did not consider other year’s data since it was not completely available. We
compared the mean group sizes using the Mann-Whitney U test, the proportions of
different age-sex compositions using the Chi-square test, and the ratios of
different age-sex using Paired Wilcoxon Signed Rank test. The density of langur
was calculated as a total number of individuals divided by the total area of
the survey (~277 ha). We used statistical analysis using R version 3.6.3. The
rate of population growth, r, between two-time points, t1 and t2, is calculated
as a rate of growth, expressed in percentage units per year:
Where P1 and P2 are the number of
individuals at times t1 and t2 respectively and the time interval (t2-t1) is
expressed in years (https://pages.uoregon.edu/rgp/PPPM613/class8a.htm Accessed
on 12 March 2021).
RESULTS
We recorded six groups of Golden
Langurs totaling 78 individuals (Table 1, Image
1&2) with the mean group size of 13.00±4.00SD (Table 2). By
excluding the data from Group 1 where we were unsure of the demographics of
some of the individuals, the age-sex composition of the population was 10.29%
(N= 7) adult males, 41.18% (N= 28) adult females, 32.35% (N= 22) juveniles and
16.18% (N= 11) infants. Of the six groups, three groups had two adult males.
The ratio of adult male to adult female was 1:4.00; adult to immature was
1:0.94; and adult female to infant was 1:0.39 (Table 2). The calculated density
showed 28.16 langurs/km2.
The number of groups recorded in
1997 was five, declined to three by 2002 (Medhi et
al. 2004), increased to 12 by 2008 and then declined to six by 2016 (Table 2).
The mean group size between 2002 and 2016 did not vary significantly (M-W U
test, U= 12.0, p= 0.517). Proportion of adult males, adult females and immature
per group in 2002 and 2016 (adult males: χ2= 2.88, df= 7, p= 0.896; adult females: χ2= 10.34, df= 7, p= 0.17; immature: χ2= 6.91, df= 7, p= 0.438) did not vary significantly (Table 2).
Although, the number of females per male in 2002 (3.40) was less than in 2016
(4.00) the difference was not significant (t= -1.313, df= 6, p= 0.237). Similarly, the number of immatures per
adult (in 2002: 1.36 and in 2016: 0.94; t= -0.844; df= 6, p= 0.431), and
number of infants per adult female (2002: 0.76 and 2016: 0.39; t= 2.144; df= 6, p= 0.076) did
not differ significantly. The population growth between 1997 and 2016 was found
to be 5.54 % (Table 3).
DISCUSSION
We examined the population
numbers and demographics of the Golden Langur in a rubber planta-tion in Assam, India between 1997 and 2016. Although the
reasons for the differences in the number of groups and the mean group size
between the study period were not well understood due to the lack of continuous
monitoring, the fluctuations in the population size could be tracked during
certain periods. The large group size in 2002 and the small group size in 2008
with many groups indicated that the population might be exhibiting fusion and
fission of the groups. Fusion and fission of groups are social traits in
primates, and also reported in Golden Langur (Biswas 2004). Group size
influences feeding time (Doran 1997; Sakura 1994), suggests that fission-fusion
may serve as a mechanism to reduce within-group feeding competition and help to
overcome the negative consequences of group living. Absence of the significant
difference in age-sex ratios between 2002 and 2016 suggests that though the
population size fluctuated, the demographical structures remained stable
despite changes in vegetation structure and species composition in the habitat.
Within the natural habitat of Chakrashila Wildlife
Sanctuary, the group size of Golden Langur ranged 3–15 individuals, with a mean
size of 7.4 and the age structure of the population comprised 49.8% adults,
33.5% juveniles and 16.7% infants (Chetry et al.
2010). Our study, however, shows that the density of Golden Langur in a rubber
plantation (28.16 langurs/km2) is much higher than in the natural
habitat of Chakrashila Wildlife Sanctuary (12.40
langurs/km2) (Chetry et al. 2020). The
annual population growth from 1997 and 2016 (Table 3) was much higher (5.54%)
than in the natural habitat of Chakrashila Wildlife
Sanctuary i.e., 1.5% annual growth from 2006 (Chetry
et al. 2010) to 2016 (Chetry et al. 2020). In the
rubber plantation, deaths of three adult female Golden Langurs due to
electrocution in 2001–2002 were reported by Medhi et
al. (2004). Medhi et al. (2004) also mentioned domestic
dogs as a possible threat for the Golden Langur population. This could affect
the population dynamics and age-sex composition since the population of Golden
Langur is small. But during this survey and our behavioral
study period (2013-2016) we did not record any incident of electrocution or dog
attack. The birth rate and immature survival rate were not different between
the rubber plantation and adjacent natural forests of Chakrashila
Wildlife Sanctuary (Shil et al. 2020). Since the
birth and immature survival rate cannot be a factor of population fluctuation
in the rubber plantation, therefore migration of animals could be the possible
reason. Furthermore, the high nucleotide diversity of the langur population at Nayekgaon’s rubber plantation (Ram et al. 2016) indicated
that gene flow between the populations of other nearby fragments was probably
still present. Rubber monocultures can provide corridors for the movement of
Golden Langurs between fragmented habitats as canopy connectivity reduces the
exposure of primates to predators (Oliveira & Dietz 2011; Cassano et al. 2014; Coleman & Hill 2014).
In areas where natural habitats
have declined, primates may be forced to use altered landscapes of a matrix
composition more frequently for feeding and traveling (Galán-Acedo
et al. 2019). Rubber agroforests that retain some degree of natural forests
support a subset of forest biodiversity in landscapes (Warren-Thomas et al.
2015). The encounter rate of Spider Monkeys Ateles
geoffroyi increased with matrix functionality in
the more disturbed region (Galán-Acedo et al. 2019).
Feeding on young leaves and fruits of rubber (Roy & Nagarajan 2018) and dry
rubber seeds by Golden Langurs (Medhi et al. 2004;
Roy & Nagarajan 2018) and use of rubber trees for sleeping (Roy & Nagarajan
2018) highlight an adaptive behavior of the langurs.
In Sumatra, Rizaldi et al. (2019) reported six out of
nine groups of East Sumatran Banded Langur Presbytis
percura adapting to feed on non-native rubber
trees which were introduced into their habitat nearly 100 years ago. At least 86 primate species (17%
of all primates) are actively
obtaining food resources from the anthropogenic landscape,
highlighting their importance for primate conservation (Asensio et al. 2009; Arroyo-Rodríguez et al. 2017). Among forest-specialised
primates, which represent 70% of the studied species, the results suggest that the
reason for the persistence of their population in the altered habitat may be
because they are able to
supplement their diet by foraging
in the modified landscape (Dunning
et al. 1992). In Batang Serangan
in northern Sumatra, a small population of the Sumatran Orangutan Pongo abelii, Thomas’s Langur Presbytis
thomasi, Long-tailed Macaque M. fascicularis fascicularis,
Southern Pig-tailed Macaque M. nemestrina, Lar
Gibbon Hylobates lar, and Silvered
Langur T. cristatus have been reported living
for several decades in a mixed agroforest system composed of Oil Palm Elaeis guineensis,
rubber trees, and remnant forest (Campbell-Smith et al. 2010). The continued
presence of Proboscis Monkey Nasalis larvatus for more than two decades in the cocoa and oil
palm plantation in Lower Kinabatangan Floodplain suggests that the species is
resilient to habitat changes (Boonratana 2013). But
the loss of critical habitats and the inability to access other nearby
fragments have allowed the species to persist only at lowered population size
and densities, and with likely changes to their behavior
and ecology (Boonratana 2013). The rate of emigration
from habitat also had a very strong predicted effect on the extinction
threshold; the higher the rate of emigration, the more habitat was needed for
persistence (Fahrig 2001). Angolan Colobus Colobus angolensis palliatus frequently travelled and foraged in
indigenous matrix vegetation (such as mangrove, wooded shrubland, and
shrubland) up to four kilometers from the nearest
forest fragments. Agricultural habitats, such as perennial plantation (coconut,
mango and cashew nut) was also used by colobus as corridor (Anderson et al. 2007).
Although initial decline in the population was observed, Golden Langurs have
shown increase in the population size over the period. A similar pattern was
also seen with other primates e.g., Nicobar Long-tailed Macaque M. f. umbrosus in Nicobar Islands (Velankar
et al. 2016), Lion-tailed Macaque M. silenus
in Western Ghats (Umapathy et al. 2011), Guerezas Colobus guereza
and Blue Monkey Cercopithecus mitis in Kakamega forests in Kenya (Mammides et al. 2008). Thus, the persistence of Golden
Langur in a relatively high density in the rubber plantation could be due to
continued gene flow between nearby populations and the value of the rubber
plantation as food resource and habitat corridor amid a disturbed,
anthropogenic landscape outside of protected areas. Continuous population
monitoring and ecological studies in such matrices would help in understanding
their adaptability for the conservation of the threatened Golden Langur.
Table 1. Group compositions of Trachypithecus geei
in rubber plantation in 2016.
|
Group # |
Adult male |
Adult female |
Juvenile male |
Juvenile female |
Infant |
Unidentified/ Doubtful |
Total |
|
1 |
2 |
2 |
1 |
1 |
0 |
4 |
10 |
|
2 |
1 |
6 |
1 |
2 |
2 |
- |
12 |
|
3 |
1 |
4 |
2 |
2 |
0 |
- |
9 |
|
4 |
2 |
8 |
2 |
1 |
5 |
- |
18 |
|
5 |
2 |
6 |
4 |
4 |
2 |
- |
18 |
|
6 |
1 |
4 |
1 |
3 |
2 |
- |
11 |
|
All total |
|
|
|
|
|
|
78 |
Table 2. Group size, age-sex
composition of Trachypithecus geei in rubber plantation in different studies.
|
Group parameters |
1997 (Srivastava et al. 2001a) |
2002 (Medhi
et al. 2004) |
2008 (Ghosh 2009) |
2016 (current study) |
|
Total groups (mean group size±SD; range) |
5 (7.6) |
3 (17.33±9.61; 7–29) |
12 (9.3) |
6 (13.00±4.00; 9–18) |
|
Total AM (mean±SD;
range) |
- |
5 (1.67±0.58; 1–2) |
- |
7 (1.40±0.55; 1–2) |
|
Total AF (mean±SD;
range) |
- |
17 (5.67±3.21; 2–8) |
- |
28 (5.60±1.67; 4–8) |
|
Total IM (mean±SD;
range) |
- |
30 (10.00±6.00; 4–16) |
- |
33 (6.60±2.41; 4–10) |
|
AM:AF |
- |
1:3.40 |
1:2.25 |
1:4.00 |
|
AD:IM |
- |
1:1.36 |
- |
1:0.94 |
|
AF:IN |
- |
1:0.76 |
- |
1:0.39 |
|
Total individuals |
38 |
52 |
112 |
78 |
Table 3. Population growth rate
of Trachypithecus geei
in rubber plantation.
|
Period |
Annual Growth rate % |
|
1997–2002 |
7.37 |
|
2002–2008 |
19.23 |
|
2008–2016 |
-3.79 |
|
1997–2016 |
5.54 |
For
figure & images - - click here
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