Dusky leaf monkey

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Dusky leaf monkey [1]
Dusky leaf monkey (8050982300).jpg
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Primates
Suborder: Haplorhini
Infraorder: Simiiformes
Family: Cercopithecidae
Genus: Trachypithecus
Species group: Trachypithecus obscurus group
Species:
T. obscurus
Binomial name
Trachypithecus obscurus
(Reid, 1837)
Dusky Leaf Monkey area.png
Dusky leaf monkey range

The dusky leaf monkey (Trachypithecus obscurus), also known as the spectacled langur or the spectacled leaf monkey, is a species of primate in the family Cercopithecidae. It is found in Peninsular Malaysia, Myanmar and Thailand, [2] and can occasionally be found in Singapore. [3] During the day, these small, folivorous primates divide in sub-groups and forage for vegetation and fruit throughout the tropical forests. [4] [5] According to the IUCN, the dusky leaf monkey's population is declining due to habitat loss, poaching, and anthropogenic land use, which prompted the IUCN to classify the species as endangered in 2015. [2]

Contents

Taxonomy

Within the Cercopithecidae family, the dusky leaf monkey is a member of the genus Trachypithecus . Although most researchers agree with this classification, others believe that this primate should be categorized under the genus Presbytis. [6] [7]

Subspecies

Researchers have also disputed the number of subspecies that exist, with some claiming that there are 11, [8] while others claim there are seven. Currently, the following seven subspecies are officially recognized: [4] [9] [10]

Description

The dusky leaf monkey can appear in different colour variations, depending on the sub-species. While dusky leaf monkeys are born with an orange coat, the colour of their fur changes as they mature into adulthood. [3] Along the abdominal area, their fur is often several shades lighter than that of their dorsal area, which can develop in shades of brown, black, or grey. Surrounding their eyes are circular patterns of bright white fur. [8] [11] [12]

The dusky leaf monkey is a rather small primate. In a study conducted by G. J Burton, the average weight of the 25 male dusky leaf monkeys that were sampled was 7.39 kilograms, while that of the 44 female dusky leaf monkeys that were sampled was 6.47 kilograms. These results suggest that dusky leaf monkeys are sexually dimorphic species, as the females were found to be, on average, 12% smaller than the males sampled. Burton's study also revealed that, among the 25 male primates, there was a direct correlation with the weight of one testicle with the weight of the other, suggesting that one testicle may be used to estimate the weight of the other. However, the female ovaries were found to not be statistically significant enough to predict the weight of one ovary with the other. [13]

Distribution

While the dusky leaf monkey's fur can develop into shades of grey, brown, or black, they are born with an orange coat. Dusky Langur infant learning to eat leaves.jpg
While the dusky leaf monkey's fur can develop into shades of grey, brown, or black, they are born with an orange coat.

The dusky leaf monkey can be found across Malaysia, Myanmar, and Thailand, where they inhabit tropical forests. [2]

Singapore population

However, these primates have occasionally been spotted in Singapore. Research conducted within the country between 2019 and 2020 revealed that three dusky leaf monkey individuals were located in August 2019 within the northern region of the island, near the body of water that borders Singapore and Malaysia. While dusky leaf monkeys are not considered native to the region, researchers speculate that they are able to swim to the country. Researchers are concerned about these migratory patterns because these primates can increase competition for resources, such as vegetation, and transfer diseases and pathogens to other native species that are not equipped to recover from them. [3] Despite this, the species is not considered an invasive species, as their colonization of Singapore is natural and not assisted by humans.

Behaviour and diet

Dusky leaf monkeys feed in the emergent and canopy layers. Dusky leaf monkey, Trachypithecus obscurus - Kaeng Krachan National Park (2).jpg
Dusky leaf monkeys feed in the emergent and canopy layers.

Numerous activity budgets have been conducted across Malaysia to study the behavioural patterns of the dusky leaf monkey. For instance, one activity budget conducted in 2016 with 12,480 primates in Teluk Bahang, Malaysia, found that, within the eight-month period, dusky leaf monkeys spent 40% of their time positioning, 33% of their time feeding, and 20% of their day moving. The sampled primates also allocated their time allo-grooming (4%), playing (2%), and foraging (1%). [14] Ten years prior, another activity budget with 18 dusky leaf monkeys was conducted at the Penang Botanical Garden, which is also located in Malaysia. Researchers at the University of Kebangsaan concluded that, within 18 days, the dusky leaf monkeys that were sampled spent 40% of their day eating, almost 24% of their day resting, and approximately 22.5% of their time moving. The dusky leaf monkeys also allocated time for autogrooming (6.52%) and allo-grooming (1.33%), among other behaviours.[ citation needed ] However, a more recent study conducted in Malaysia from November 2017 to February 2018 in Bukit Soga Perdana, a forested area that is heavily influenced by industrial activity, concluded that the dusky leaf monkeys sampled spent the majority of their days moving, although these results were skewed due to unfavourable weather conditions that occurred during observations. [8]

Dusky leaf monkeys live in troops that separate into sub-groups while scavenging for food. They tend to consume leaves growing at higher elevations in the forest canopy. They often rest at these high elevations to feed on their foraged vegetation. [15] [8] Fruit availability is season-dependent, and although research suggests that the dusky leaf monkey consumes more vegetation that fruit, it prefers to eat fruit when it is available. [5]

Research suggests that hostile behaviour within troops does not occur often. A study conducted in 1996 by researchers at the University of St. Andrews revealed that, after a group of dusky leaf monkeys engage in aggressive behaviour, conflict resolution occurs more frequently and much faster afterwards than within other primate species. In fact, reconciliation among dusky leaf monkeys can occur as quickly as 60 seconds after fighting, and can be instigated by either the aggressor or the receiver through gestures such as embracing. [16]

Mating

In another study conducted by Burton, 44 male dusky leaf-monkeys were sampled and the seminiferous tubules within each gonadal were observed. Burton concluded that the seminiferous tubules within each gonadal remained the same size throughout the year, and that there was no evidence of seasonal variation in testicular weight. This reveals that the male dusky leaf monkey does not have a seasonal mating period and are able to reproduce throughout the year. Burton suggests that this may be the case due to the continuous, warm climates experienced within Southeast Asia, as the mating period for many seasonal breeders occurs during warming climates. [17]

Conservation

As of 2015, the dusky leaf monkey is listed as an endangered species in the IUCN Red List. Notably, anthropogenic land-use within Southeast Asian forests have resulted in the endangerment of the dusky leaf monkey's natural habitat, resulting in noticeable population declines. [18] [8] However, the dusky leaf monkey also faces other threats brought on through anthropogenic activities and the introduction of predators within their habitat. Notably, domesticated dog packs have been reported to hunt and kill the dusky leaf monkey. [19] The construction of roads within tropical forests has led to a large increase in road mortality among dusky leaf monkeys, and is seen to be one of the more prominent threats to the dusky leafy monkey's survival, along with habitat loss, habitat degradation, and poaching. [20] [18] While the dusky leaf monkey is often killed for their meat, [2] there are other incentives to poach them as well, as they are considered agricultural pests across Southeast Asia. [4] In the 1960s, this prompted Malaysian business owners to shoot them as they were feeding on leaves within rubber plantations. [13] [17] Infant dusky leaf monkeys are also hunted and sold as pets internationally. However, when owners attempt to domesticate these primates, they are often not properly cared for and die as a result. [3]

Collective action is being taken to help conserve the dusky leaf monkey. In 1977, the dusky leaf-monkey had been introduced and listed under appendix II in the CITES legislation. [21] Species under appendix II are considered to be near threatened or endangered. The trade of appendix II species is heavily regulated, and often illegal. [22]

Related Research Articles

<i>Semnopithecus</i> Genus of Old World monkeys

Semnopithecus is a genus of Old World monkeys native to the Indian subcontinent, with all species with the exception of two being commonly known as gray langurs. Traditionally only the species Semnopithecus entellus was recognized, but since about 2001 additional species have been recognized. The taxonomy has been in flux, but currently eight species are recognized.

<span class="mw-page-title-main">Colobinae</span> Subfamily of Old World monkeys

The Colobinae or leaf-eating monkeys are a subfamily of the Old World monkey family that includes 61 species in 11 genera, including the black-and-white colobus, the large-nosed proboscis monkey, and the gray langurs. Some classifications split the colobine monkeys into two tribes, while others split them into three groups. Both classifications put the three African genera Colobus, Piliocolobus, and Procolobus in one group; these genera are distinct in that they have stub thumbs. The various Asian genera are placed into another one or two groups. Analysis of mtDNA confirms the Asian species form two distinct groups, one of langurs and the other of the "odd-nosed" species, but are inconsistent as to the relationships of the gray langurs; some studies suggest that the gray langurs are not closely related to either of these groups, while others place them firmly within the langur group.

<i>Trachypithecus</i> Genus of Old World monkeys

Trachypithecus is a genus of Old World monkeys containing species known as lutungs, langurs, or leaf monkeys. Their range is much of Southeast Asia.

<i>Presbytis</i> Genus of south-east Asian monkeys

Presbytis is a genus of Old World monkeys also known as langurs, leaf monkeys, or surilis. Members of the genus live in the Thai-Malay Peninsula, on Sumatra, Borneo, Java and smaller nearby islands.

<span class="mw-page-title-main">Silvery lutung</span> Species of Old World monkey

The silvery lutung, also known as the silvered leaf monkey or the silvery langur, is an Old World monkey. It is arboreal, living in coastal, mangrove, and riverine forests in Peninsular Malaysia, Sumatra, Borneo, Java, and other nearby islands. It is the type species of its species group.

<span class="mw-page-title-main">Phayre's leaf monkey</span> Species of Old World monkey

Phayre's leaf monkey, also known as Phayre's langur, is a species of Old World monkey native to South Asia and Southeast Asia, namely India, Bangladesh, and Myanmar. Populations from further east are now thought to belong to other species. It is listed as Endangered on the IUCN Red List and is threatened by hunting and loss of habitat. The species epithet commemorates Arthur Purves Phayre.

<span class="mw-page-title-main">Raffles' banded langur</span> Species of primate

The Raffles' banded langur, also known as the banded leaf monkey or banded surili, is a species of primate in the family Cercopithecidae. It is endemic to Singapore and southern Peninsular Malaysia. The species underwent taxonomic revisions in 2019 and 2020, in which two former subspecies were elevated to separate species. As a result, the Raffles' banded langur meets the criteria for being listed as critically endangered by the IUCN. It is mainly threatened by habitat loss.

<span class="mw-page-title-main">Hose's langur</span> Species of Old World monkey

Hose's langur is a species of primate in the family Cercopithecidae endemic to the island of Borneo, including Brunei, Kalimantan (Indonesia), and East Malaysia. Its natural habitat is subtropical or tropical dry forests. It is threatened by habitat loss. It was first identified in Kutai National Park and Sangkulirang Peninsula, East Kalimantan, Indonesia, in 1985.

<span class="mw-page-title-main">Black-crested Sumatran langur</span> Species of Old World monkey

The black-crested Sumatran langur is a species of primate in the family Cercopithecidae. It is endemic to Sumatra in Indonesia. Its natural habitat is subtropical or tropical dry forests. It is threatened by habitat loss.

<span class="mw-page-title-main">Mentawai langur</span> Species of Old World monkey

The Mentawai langur is a species of primate in the family Cercopithecidae. It is endemic to the Mentawai Islands in Indonesia. Its natural habitat is subtropical or tropical dry forests. The Siberut langur was formerly considered a subspecies of the Mentawai langur.

<span class="mw-page-title-main">White-thighed surili</span> Species of Old World monkey

The white-thighed surili is a species of primate from the family of old world monkeys (Cercopithecidae). This species lives arboreal amongst the sub-montane forests. It is endemic to the Thai-Malay Peninsula, the Riau Archipelago and Sumatra. In addition, the white-thighed surili contain four subspecies: siamensis (nominate), cana, paenulata and rhionis, are recognized here. Furthermore, they are characterized by the white patches located on the outside of their legs, which is what gives them their name. Additionally, they can be referred to as pale-thighed langur/surili. These primates are an important species for the diversity of forest environments in the Malaysian area.

<span class="mw-page-title-main">Thomas's langur</span> Species of Old World monkey

Thomas's langur, also known as the North Sumatran leaf monkey or Thomas's leaf monkey, is a species of primate in the family Cercopithecidae. It is endemic to northern Sumatra, Indonesia, not living to the south and east of Lake Toba and the Alas and Wampu rivers. Its natural habitat is subtropical or tropical dry forests. It is threatened by habitat loss. Its native names are reungkah in Acehnese and kedih in Alas. It can be found in Gunung Leuser National Park, where substantial populations exist in Ketambe and Bukit Lawang.

<span class="mw-page-title-main">Germain's langur</span> Species of Old World monkey

Germain's langur is an Old World monkey native to Thailand, Myanmar, Cambodia, Laos and Vietnam. The monkey was previously included in Trachypithecus cristatus and Trachypithecus villosus.

The Indochinese black langur is a poorly known Old World monkey native to Laos and adjacent Vietnam. It was originally described as a subspecies of T. auratus, but was later found to be a member of the T. francoisi group, with some maintaining it as a subspecies of that species. In 2001, it was recommended treating it as a separate species.

<span class="mw-page-title-main">Selangor silvered langur</span> Species of Old World monkey

The Selangor silvered langur is a species of leaf monkey found on the west coast of Peninsular Malaysia. It had been previously considered a form of silvery lutung. Roos and colleagues elevated this population to a subspecies level, Trachypithecus cristatus selangorensis, in 2008. It has since come to be regarded by primatologists as a separate species, Trachypithecus selangorensis.

<span class="mw-page-title-main">Robinson's banded langur</span> Species of primate

Robinson's banded langur, also known as Robinson's banded surili, is a species of monkey in the family Cercopithecidae. It was formerly considered a subspecies of the Raffles' banded langur Presbytis femoralis, but genetic analysis revealed that it is no more related to Raffles' banded langur than it is to several other Presbytis species. It lives in the northern Malay Peninsula, including southern Burma and Thailand. It is listed as near threatened by the IUCN.

<span class="mw-page-title-main">Siberut langur</span> Species of monkey

The Siberut langur is a species of monkey in the family Cercopithecidae. It was formerly considered a subspecies of the Mentawai langur, Presbytis potenziani but genetic analysis revealed that these are separate species. The Siberut langur is native to the island of Siberut in Indonesia. It is listed as endangered by the IUCN.

<span class="mw-page-title-main">Sabah grizzled langur</span> Species of monkey

The Sabah grizzled langur, also known as the Saban grizzled langur, is a species of monkey in the family Cercopithecidae. It was formerly considered a subspecies of Hose's langur, Presbytis hosei. The Sabah grizzled langur is native to the island of Borneo in the province of Sabah in Malaysia, with part of its range in Indonesia. It is listed as endangered by the IUCN due primarily to habitat loss, fragmentation and hunting.

<span class="mw-page-title-main">Miller's langur</span> Species of leaf monkey (mammal)

Miller's langur, also known as Miller's grizzled langur or Kutai grey langur, is a species of leaf monkey. It is endemic to East Kalimantan on the island of Borneo in Indonesia. It is one of the world's most endangered primates, and was at one time thought to be extinct, until it was rediscovered in 2012.

<span class="mw-page-title-main">Popa langur</span> Species of mammal

The Popa langur is a species of primate in the family Cercopithecidae. It occurs only in Myanmar and was named after Mount Popa, where a population of 100 of the monkeys live. It is listed as Critically Endangered on the IUCN Red List, as the wild population is thought to comprise 200 to 250 mature individuals.

References

  1. ↑ Groves, C. P. (2005). Wilson, D. E.; Reeder, D. M. (eds.). Mammal Species of the World: A Taxonomic and Geographic Reference (3rd ed.). Baltimore: Johns Hopkins University Press. p. 177. ISBN   0-801-88221-4. OCLC   62265494.
  2. 1 2 3 4 5 Boonratana, R.; Ang, A.; Traeholt, C.; Thant, N.M.L. (2020). "Trachypithecus obscurus". IUCN Red List of Threatened Species . 2020: e.T22039A17960562. doi: 10.2305/IUCN.UK.2020-2.RLTS.T22039A17960562.en . Retrieved 15 November 2021.
  3. 1 2 3 4 Ang, A.; Jabbar, S.; Khoo, M. (2020). "Dusky Langurs Trachypithecus obscurus (Reid, 1837) (Primates: Cercopithecidae) in Singapore: potential origin and conflicts with native primate species". Journal of Threatened Taxa. 12 (9): 15967–15974. doi: 10.11609/jott.5818.12.9.15967-15974 . S2CID   225650126.
  4. 1 2 3 4 Nor Rahman Aifat; Muhammad Abu Bakar Abdul-Latiff; Christian Roos; Badrul Munir Md-Zain (2020). "Taxonomic Revision and Evolutionary Phylogeography of Dusky Langur (Trachypithecus obscurus) in Peninsular Malaysia". Zoological Studies. 59 (59): 2–11. doi:10.6620/ZS.2020.59-64. PMC   8181166 . PMID   34140981.
  5. 1 2 Ruslin, Farhani; Matsuda, Ikki; Md-Zain, Badrul Munir (2019-01-01). "The feeding ecology and dietary overlap in two sympatric primate species, the long-tailed macaque (Macaca fascicularis) and dusky langur (Trachypithecus obscurus obscurus), in Malaysia". Primates. 60 (1): 41–50. doi:10.1007/s10329-018-00705-w. ISSN   1610-7365. PMID   30564972. S2CID   56170185.
  6. ↑ Napier, John Russell; Napier, P. H. (1967). A handbook of living primates: morphology, ecology and behaviour of nonhuman primates. London: Academic. ISBN   0-12-513850-4. OCLC   255860.
  7. ↑ Thongnetr, Weera; Sangpakdee, Wiwat; Tanomtong, Alongklod; Nie, Wenhui; Raso, Sayam; Pinthong, Krit (2021-11-27). "The chromosomal homology between dusky langur (Trachypithecus obscurus Ried, 1837) and human (Homo sapiens) revealed by chromosome painting". The Nucleus. 65 (2): 233–237. doi:10.1007/s13237-021-00381-0. ISSN   0976-7975. S2CID   244740122.
  8. 1 2 3 4 5 Siti-Kauthar, M.; Najmuddin, M. F.; Md-Zain, B. M.; Abdul-Latiff, M. A. B. (2019). "PrimaTourism: preliminary study on activity budget of dusky leaf monkey Trachypithecus obscurus obscurus in Bukit Soga Perdana, Batu Pahat, Johor". IOP Conference Series: Earth and Environmental Science. 269 (1): 012045. Bibcode:2019E&ES..269a2045S. doi:10.1088/1755-1315/269/1/012045. S2CID   201211018.
  9. 1 2 Don E. Wilson; DeeAnn M. Reeder (2005). Mammal species of the world : a taxonomic and geographic reference (3rd ed.). Baltimore: Johns Hopkins University Press. ISBN   0-8018-8221-4. OCLC   57557352.
  10. 1 2 "Trachypithecus obscurus". Integrated Taxonomic Information System . Retrieved 2 November 2021.
  11. ↑ Groves, Colin (2001). Primate Taxonomy. Washington, DC: Smithsonian Books. ISBN   978-1560988724.
  12. ↑ Roos C, Boonratana R, Supriatna J, Fellowes JR, Groves CP, Nash SD, Rylands AB, Mittermeier RA (2014). "An updated taxonomy and conservation status review of Asian primates". Asian Primates Journal. 4.
  13. 1 2 Burton, G.J. (1981). "The Relationship Between Body and Gonadal Weights of the Dusky Leaf Monkey (Presbytis obscura)". International Journal of Primatology. 2 (4): 351–368. doi:10.1007/BF02693484. S2CID   42972066.
  14. ↑ Yap, J.; Ruppert, N.; Fadzly, N. (2016). Activity patterns and diet of a group of wild dusky leaf monkeys (Trachypithecus obscurus) in Penang, Malaysia. Seminar Ekologi Malaysia.
  15. ↑ G. Gene Montgomery (1978). The ecology of arboreal folivores : a symposium held at the Conservation and Research Center, National Zoological Park, Smithsonian Institution, May 29-31, 1975. Washington, D.C.: Smithsonian Institution Press. ISBN   0-87474-646-9. OCLC   4004986.
  16. ↑ Arnold, K.; Barton, R. (2000). "Postconflict Behavior of Spectacled Leaf Monkeys (Trachypithecus obscurus). I. Reconciliation". International Journal of Primatology. 22 (2): 243–266. doi:10.1023/A:1005623631652. S2CID   7025717 – via ResearchGate.
  17. 1 2 Burton, G. J. (1984). "Testicular histology of the dusky leaf monkey (presbytis obscura) as it relates to birth pattern in Peninsular Malaysia". International Journal of Primatology. 5 (2): 183–195. doi:10.1007/BF02735740. ISSN   0164-0291. S2CID   41458567.
  18. 1 2 Boonratana, Ramesh. "Of road kills and dead langurs. Malaysian Naturalist". CAB Reviews Perspectives in Agriculture Veterinary Science Nutrition and Natural Resources.
  19. ↑ MOHD FAUDZIR, N.; Haris, H.; Atiqah Norazlimi, N.; Munir Md Zain, B. "PREDATION OF DOMESTIC DOGS (Canis lupus familiaris) ON SCHLEGEL'S BANDED LANGUR (Presbytis neglectus) AND CRESTED HAWK-EAGLE(Nisaetus cirrhatus) ON DUSKY LEAF MONKEY (Trachypithecus obscurus)IN MALAYSIA". Journal of Sustainability Science and Management. 14 (6): 43.
  20. ↑ Lappan, Susan. "Primate Research And Conservation In Malaysia" (PDF). CAB Reviews Perspectives in Agriculture Veterinary Science Nutrition and Natural Resources: 5.
  21. ↑ "Species+". speciesplus.net. Retrieved 2022-04-11.
  22. ↑ "Convention on International Trade in Endangered Species of Wild Fauna and Flora | CITES". cites.org. Retrieved 2022-04-11.
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