Tarsius dentatus

Geographic Range

Tarsius dentatus (Dian's tarsier) from the northern part of Sulawesi, Indonesia was originally described as a new species in 1921 by Miller and Hollister. In 1991, Niemitz and coworkers characterized a purported new species named Tarsius dianae . However, in 1997, Shekelle and coworkers proposed that T. dianae was a synonym of T. dentatus . Further analysis is required to determine whether they are the same species. Dian's tarsiers occur predominantly in central Sulawesi, an island of Indonesia. Their presence is largely determined by their vocalizations (Nietsch and Kopp, 1998). Gursky (1998, 2007) states that most members of the species live in the Morowali Nature Reserve and Lore Lindu National Park.

• Biogeographic Regions
• oriental oriental
  • native native

• Other Geographic Terms
• island endemic island endemic

Habitat

This tarsier species lives both in primary and secondary lowland rainforests in central Sulawesi. Field studies reveal that the population density of T. dentatus varies from 129 to 136 individuals per square kilometer (Gursky, 2007). At an altitude of 500 to 1000 meters, population density is estimated to be 180 individuals, while at 1000 to 1500 meters, only 57 individuals per square kilometer were observed. The population was also approximately ten times more dense in secondary forests than primary forests.

• Habitat Regions
• tropical tropical
• terrestrial terrestrial

• Terrestrial Biomes
• rainforest rainforest

Physical Description

Tarsiers are easily distinguished by their size, large orbits, and elongated tarsal bones. The head of tarsiers is round with a reduced muzzle and short neck. Tarsius dentatus is larger than T. pumilus but similar in size to T. tarsius . The coat color of Dian's tarsiers is grayish-buff and the tail is naked except for some hair at the end. Tarsius dentatus can be identified by the presence of short, white hairs flanking the upper lip and in the middle of the lower lip. It can be distinguished from T. spectrum by the lack of brown pelage at the hip, thigh, or knee and darker pigmentation on the tail, fingers, toes, and nails. Tarsius dentatus also has a more conspicuous black line of fur surrounding the eyes than does T. spectrum . The ears of T. dentatus are shorter and wider than those of T. spectrum and there is a hairless patch at the base of each ear. The fur of subadults is slightly more gray and woolly than those of T. spectrum . The digits are padded to allow gripping with grasping hands and feet. The finger nails of T. dentatus are curved, pointed, and dark. Females have two pairs of mammary glands.

Because this species is nocturnal and lacks a tapetum lucidum, its eyes are enlarged to a diameter of approximately 16 mm. The eyes appear asymmetrical and not fully opened compared to those of T. spectrum . Tarsius dentatus is able to rotate its head 180 degrees. The nasal region is covered with short hair except for an area of naked skin around the nostrils. Tarsius dentatus has well-developed, laterally folded nostrils. It also has large ears, but they are short compared to those of T. spectrum .

Tarsius dentatus has a more delicate mandible than that of T. spectrum . The dental formula of this species is 2/1:1:3:3, and it has large, pointed upper and lower incisors. The upper canines are small.

Tarsiers are small and nocturnal. They do not exhibit torpor, a state of dormancy during food shortages.

• Other Physical Features
• endothermic endothermic
• homoiothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• sexes alike

Reproduction

Although tarsiers were believed to be monogamous, studies have shown that Sulawesi tarsiers actually exhibit facultative polygyny and form strong pair bonds. Males are more territorial than females and have a greater home range. The mating system of Tarsius dentatus remains to be studied.

The mating behavior of Tarsius dentatus has not been studied. Before the onset of female ovulation, both male and female tarsiers groom themselves and mark their environment more frequently with urine and feces. Males have been observed to chase after estrous females while chirping like a bird, and they examine female genitals by sniffing. Vocalizations by both sexes also increase in frequency, and include a "piercing-twittering 'chit-chit'".

The reproductive behavior of Tarsius dentatus has not been studied. In general, tarsier females give birth to one offspring per year with a long gestation period. The rate of fetal and postnatal development of tarsiers is among the slowest of all mammals. Tarsier infants are also proportionally the largest of all non-anthropoid primate infants. Most of their mass is composed of brain mass, eyes, and cranium. The dedication of resources to the brain leads to the rapid development of foraging and locomotor behaviors.

Pregnancy is often very costly for female tarsiers. Pregnant females have low mobility, impaired foraging abilities, and maintain smaller home ranges than their non-pregnant counterparts. Furthermore, postpartum females cannot lactate and transport infants at the same time due to energy restrictions. They often "park" their offspring on a secure branch. Pregnant females were observed in a year-round study, and there appears to be no seasonal variation in mating.

Studies on T. spectrum have revealed that young tarsier females stay with their parents until adulthood, whereas young males leave as juveniles.

• Key Reproductive Features
• iteroparous iteroparous
• year-round breeding year-round breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• viviparous viviparous

Pairs of female and male tarsiers stay together to form close bonds for at least 15 months. Tarsier infants can cling to a vertical surface. Female progeny stay with their parents until adulthood, whereas young males leave during youth. Tarsier mothers and young have been reported to exhibit reciprocal sniffing after birth as a way of recognition.

• Parental Investment
• precocial precocial
• pre-fertilization
  • provisioning
  • protecting
    • female
• pre-hatching/birth
  • provisioning
    • female
  • protecting
    • female
• pre-weaning/fledging
  • provisioning
    • female
  • protecting
    • female
• pre-independence
  • provisioning
    • female
  • protecting
    • female
• extended period of juvenile learning

Lifespan/Longevity

Tarsius dentatus has never been kept in captivity, but in general tarsiers in captivity live an average of 5 years with a maximum of 12 years.

Behavior

This species has been described to live in groups of less than 8 individuals composed of 1 adult male and 1 to 3 adult females and their offspring. They spend the day sleeping in a group-specific sleeping site, and at night they hunt and eat. Tremble observed that T. dentatus sleeps in groups in locations with dense foliage, vine tangles, fallen logs, and tree cavities (Gursky, 2007). Although they prefer to sleep in strangling figs, Dian's tarsiers can sleep in a variety of other sites. Sleeping sites were found at the periphery of home ranges, which implies territorial behavior in Tarsius dentatus to refresh their scent marks. At night, the breakdown of activities of T. dentatus is as follows: 44% foraging, 28% traveling, 21% resting, and 7% resting. Dian's tarsiers were observed to rest and move about randomly for most of the night after 4 hours of leaping. Before sunrise, adult and subadult tarsiers perform duets to strengthen group bonding and advertise their territories. Subsequently, triggered by the territorial duet songs, the tarsiers move across great distances as fast as 100 m in 15 minutes to arrive at their sleeping sites.

Dian's tarsiers are arboreal and classified as vertical clingers and leapers. Other modes of locomotion include hopping, quadrupedalism, and cantering. Unlike T. spectrum , this species spends more time quadrupedally walking on horizontal supports (Schwartz, 2003).

This species identifies uses urine for scent marking.

• Key Behaviors
• arboreal arboreal
• scansorial
• saltatorial saltatorial
• nocturnal nocturnal
• crepuscular crepuscular
• motile motile
• sedentary sedentary
• territorial territorial
• social social

Home Range

The home range of this species, studied from radio-tracking, was described as smaller than that of T. spectrum . The territory for one male was measured to be 0.8 ha, and 0.5 ha for three additional individuals. However, further studies need to verify the accuracy of these measurements because Gursky noted the effect of heavy radio collars on the behavior of tarsiers. Additional studies by Merker in 2006 showed that the home ranges were 1.6 to 1.8 ha. Female home ranges were as large as 1.08 to 1.8 ha, which is smaller than the 2.3 to 3.1 ha reported for Tarsius spectrum . Home ranges were smaller in slightly disturbed forests in which food and other resources, such as trees for locomotion and sleeping, were scarce. No seasonal fluctuation in range size was observed when insect population density varied.

Communication and Perception

Males and females communicate with a special call known as the "male-female duet" in which females and males emit differently pitched sounds for 45 seconds at a sleeping site before dawn. There is regional variation in duet calls. The female begins calling by lowering the frequency pitch 16 to 9 kHz, continues her call at 7 or 8 to 1 kHz, and concludes by bringing the pitch back up to 9 to 16 kHz with a range of 1 to 9 kHz. Similarly, the male's pitch falls from 10 kHz to 5 kHz at the beginning and steadily rises to 14 kHz until the end. It is thought that the duets serve to prevent conflict by warning potential intruders of the claimed territory and of already paired individuals.

The species also identifies scent marks made from secreted urine and other substances from the epigastric glands.

• Communication Channels
• visual visual
• tactile tactile
• acoustic acoustic
• chemical chemical

• Other Communication Modes
• duets duets
• scent marks scent marks

• Perception Channels
• visual visual
• tactile tactile
• acoustic acoustic
• chemical chemical

Food Habits

Tarsiers are primarily insectivores that hunt by visual predation and feed on crickets ( Gryllidae ), grasshoppers ( Orthoptera ), and moths ( Lepidoptera ). They also eat small lizards and crustaceans, such as shrimps, in captivity. Tarsiers capture prey by carefully watching prey movements and leaping forward suddenly to capture prey in both hands. The food is chewed with a side-to-side motion of the jaw while the tarsier sits on its hind limbs grasping a tree branch. Tarsiers also ingest water by lapping, or take in liquid using the tongue. However, the specific eating habits of Tarsius dentatus remain to be studied.

• Primary Diet
• carnivore carnivore
  • insectivore insectivore

• Animal Foods
• reptiles
• insects

Predation

Predators of tarsiers are not well studied, but Gursky (2007) suggests that they include birds of prey ( Falconiformes ), civets ( Viverra ), and snakes ( Serpentes ). In the Merker etal. (2005) field study of Tarsius dianae no predation was observed.

Ecosystem Roles

Tarsiers capture and eat live animal prey at night. Hence, their role in the ecosystem has been compared to that of an owl. Tarsiers prefer to prey on insects active at night that experience less dramatic seasonal fluctuations in population. Tarsier predation minimizes competition because other insectivores such as bats and birds cannot easily maneuver through the dense understory of the forest at night. Tarsius dentatus also serves as a host for many common parasites. Through fecal analysis, Niemitz et al. (1991) found intestinal parasites including Entamoeba and two Digenea trematode species, none of which are present in T. spectrum .

Economic Importance for Humans: Positive

Spectral tarsiers have been a popular tourist attraction in Tangkoko, northern Sulawewsi (Fitch-Snyder, 2003). In the future, when Tarsius dentatus is better studied and more popular, Morowali Nature Reserve and Lore Lindu National Park might serve as sites for economic tourism.

Tarsiers are an ancient line of primates existing for at least forty million years. They occupy a unique primate niche and have many morphological and behavioral specializations. Tarsius dentatus is invaluable to the scientific and education communities for understanding the origin and evolution of haplorhine primates .

• Positive Impacts
• ecotourism ecotourism
• research and education

Economic Importance for Humans: Negative

There are no known adverse effects of Tarsius dentatus on humans.

Conservation Status

Tarsius dentatus is categorized as low risk on multiple conservation lists because of their nocturnal habits, ability to adjust to disturbed habitats, and because they reside in large, protected parks such as Lora Lindi (also Lora Lindu). Despite efforts to preserve these parks, the species is still threatened by habitat destruction and hunting by humans. Lore Lindi National Park is surrounded by many agrarian communities that hunt within the park and use timber and rattan as a source of income. Similarly, Morowali Nature Reserve also protects a group of endemic slash-and-burn horticulturalists, Wana, who hunt tarsiers with dogs and blowguns and burn the land for dry rice agriculture.

Other Comments

Karyotyping of this species by Niemitz et al. (1991) revealed that Tarsius dentatus has 46 chromosomes made of 5 pairs of acrocentric chromosomes and 17 meta- or submetacentric pairs, whereas T. syrichta has 80 chromosomes made of 7 meta- or submetacentric pairs and 33 acrocentric chromosomal pairs.

Additional Links

Encyclopedia of Life

Contributors

Tanya Dewey (editor), Animal Diversity Web.

Liubin Yang (author), Yale University, Eric Sargis (editor, instructor), Yale University.

References

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Doyle, G. 1979. Development of Behavior in Prosimians with Special Reference to the Lesser Bushbaby, Galago senegalensis moholi . Pp. 157-206 in The Study of Prosimian Behavior . New York: Academic Press, Inc..

Fitch-Snyder, H. 2003. History of Captive Conservation of Tarsiers. Pp. 277-295 in Tarsiers: The Past, Present, and Future . New Brunswick: Rutgers University Press.

Flannery, S. 2007. "The Primata" (On-line). Primate Fact Sheets. Accessed May 09, 2007 at http://members.tripod.com/uakari/tarsius_dianae.html .

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Gursky, S. 2007. The Spectral Tarsier . New Jersey: Pearson Education, Inc..

Gursky, S. 1998. Conservation Status of the Spectral Tarsier. Folia Primatol , 69: 191-203.

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Jablonski, N. 2003. The Evolution of the Tarsiid Niche. Pp. 35-49 in Tarsiers: The Past, Present, and Future . New Brunswick: Rutgers University Press.

Merker, S., I. Yustian, M. Mühlenberg. 2005. Responding to forest degradation: altered habitat use by Dian's tarsier Tarsius dianae in Sulawesi, Indonesia. Oryx , 39/02: 189-195. Accessed May 09, 2007 at http://www.journals.cambridge.org/action/displayAbstract?fromPage=online&aid=301004 .

Merker, S. 2006. Habitat-specific ranging patterns of Dian's tarsiers (Tarsius dianae) as revealed by radiotracking. American Journal of Primatology , 68: 111-125. Accessed May 09, 2007 at http://www.interscience.wiley.com .

Niemitz, C., A. Nietsch, S. Warter, Y. Rumpler. 1991. Tarsius dianae : A New Primate Species from Central Sulawesi (Indonesia). Folia Primatologica , 56: 105-116.

Nietsch, A., M. Kopp. 1998. Role of Vocalization in Species Differentiation of Sulawesi Tarsiers. Folia Primatologica , 69: 371-378.

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Schwartz, J. 2003. How Close Are the Similarities between Tarsius and Other Primates?. Pp. 50-96 in Tarsiers: The Past, Present, and Future . New Brunswick: Rutgers University Press.

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