Contributions to Zoology, 69 (3) (2000)Vincent Nijman: Geographic distribution of ebony leaf monkey Trachypithecus auratus (E. Geoffroy Saint-Hilaire, 1812) (Mammalia: Primates: Cercopithecidae)
Discussion

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Habitat and range

Fig. 1. shows the natural forest cover on the islands of Java, Bali and Lombok (after RePPProT 1990). Note that many smaller forest areas, including coastal fringes of mangrove forest, do not show at the scale used. The map also indicates the forty-two areas from where the species has been recorded. Undoubtedly, the species might be present in other areas not yet surveyed, but the present listing probably gives a fairly accurate account of the species’ distribution. Furthermore, it clearly illustrates the severe degree of fragmentation of populations of ebony leaf monkey, possibly having its effect on the survival of the species.

Oates et al. (1994) erroneously restrict the range of the genus Trachypithecus as far east as the Greater Sundas, excluding Lombok, but include this island, as well as Bali, in the range of the genus Presbytis. P. comata ranges on Java as far east as Mt. Lawu, on the border of Central and East Java (Nijman, 1997), but does not occur on Bali or Lombok.

The islands of Java and Bali are situated on the Sunda Shelf, while Lombok forms part of Wallacea, the transition zone between the Oriental and Australian faunal regions. Although not providing a total barrier, the deep water of the Lombok Strait has restricted contact with the Lesser Sunda Islands. In Malesia, primates are largely restricted to the Sundaic region, with only tarsiers Tarsier spp. having reached Sulawesi, and macaques Macaca spp. reaching into Sulawesi and the Lesser Sundas. Ebony leaf monkey is the only colobine that ranges into Wallacea. It has been suggested, firstly by A. Everrett (Hartert, 1896), that the species was almost certainly introduced by Balinese Rajahs on Lombok. Alternatively, the possibility that the species might have been a recent colonizer has been considered (e.g., Eudey, 1987).

De Iongh et al. (1982) observed black monkeys on the Kangean Islands, and reported the possible presence of ebony leaf monkeys on the islands. The Kangean Islands are a group of rather isolated islands situated on the eastern edge of the Sunda Shelf, c. 125 km east of Madura and c. 125 km north of Bali. Bergmans and van Bree (1986), referring to the above mentioned observations, reported the possible presence of the species on Kangean and speculated about the introduction of a number of mammals on the islands by humans.

In an attempt to clearify the distribution of ebony leaf monkeys on the Kangean island, I visited Kangean for five consecutive days in August 1997. Throughout the island long-tailed macaques were numerous (cf. de Iong et al., 1982), but no ebony leaf monkey was seen or heard. The pelage of long-tailed macaques on Kangean Island is darker than those from mainland Java, and was described as dark grey (rather than brown with a reddish or greyish gloss), often looking blackish under field conditions. For long-tailed macaques to be darker pigmented is a known phenomenon on small islands on the Sunda Shelf (e.g., Simuelue: van Schaik and van Noordwijk, 1985; Nias: Miller, 1903; Karimunjawa and Bawean: Sody, 1949). Local inhabitants and officers of the forestry departement on the island, some of which were familiar with ebony leaf monkeys from mainland Java or Bali, claimed that the species was not present on the island. Both Dr. B. van Helvoort (pers. comm. 1997) and Dr Ir H.H. de Iongh (in litt. 1999) do not recall having seen ebony leaf monkeys on the Kangean Islands. In conclusion, ebony leaf monkeys are most likely not present on the Kangean Islands nor are there any indications that they were present in the distant past. The reports of ‘black monkeys possibly or likely ebony leaf monkeys’ (de Iongh et al., 1982; Bergmans and van Bree, 1986), most likely refer to long-tailed macaques, which can have a rather dark pelage coloration on the island.

Ebony leaf monkeys are most likely absent from the island of Madura as well. The island is very arid and virtually all forest has long disappeared (Whitten et al., 1996). During three days of surveying on the island in August 1997 no suitable area of forest was found on the island, and no information indicating the presence of ebony leaf monkeys was received. Few remnants of mangrove forest found on the southern coast between Nipah and Jrengik were to small and the trees too stunted to offer suitable habitat.

Ebony leaf monkey, however, do occur on the islands of Sempu, several hundreds of meters off the coast near the Lebakhardjo and Bantur forests [29 in the area account and in Figure 1, and Nusa Barung [31], which is situated 10 km of the southern coast of the eastern part of Java. At least three scenarios can account for the presence of the species on these islands, none of which is mutually exclusive. Firstly, the ebony leaf monkeys on Sempu and Nusa Barung can be considered relict populations from a time when the sea level was lower as to provide a ‘land bridge’ to the islands. As Nusa Barung is separated from mainland Java by a relative deep strait, this relict population must have become isolated somewhere at the end of the last glacial period, at least 8-10,000 YBP, while for Sempu the separation may be dated somewhat later. Secondly, the species might have been introduced by man. Ships might have transported the animals to the islands, where it was, accidentally or deliberately, set free. Thirdly, the species has been able to (re)colonize suitable islands without the help of man, anytime from the time the islands became separated up to the present day. For long-tailed macaques Wallace (1869) already noted that “this species is very frequent on the banks of rivers, and may have been conveyed from island to island on trees carried down by floods.” Similarly, ebony leaf monkeys might have spread naturally east to Lombok. Since the last ice-age there has been more than sufficient time to colonize an island with a similar climate and vegetation, and on which no other (competiting) colobine could exclude it. Given the species ability to occupy mangrove and beach forests, and the relative narrowness of the straits (although the Lombok Strait is broader that the Bali Strait), this possibility cannot be ruled out a priori.

FIG2

Pl. I. Three individuals of the erythristic pelage morph of ebony leaf monkey Trachypithecus auratus (E. Geoffroy Saint-Hilaire, 1812), Taman Safari Zoo, Cisarua, West Java 1999.

Van der Zon (1978) reported the species to be present in mangrove, swamp, and lowland rainforest up to 1500 m a.s.l., often near human settlements. Medway (1970) considered its habitat to be inland forest from the lowlands up to almost 2,000 m a.s.l. Bennett and Davies (1994), in contrast, claim that the species is restricted to coastal and riverine habitats. In fact, the species occurs over a wide range of habitats, from beach forests and swamp forests to dry deciduous forests, and from mangrove, riverine, and lowland rain forest to upper montane forests up to 3,500 m a.s.l.

Probably the species‘ ability to cope with considerable amounts of leaves in its diet allows them to live in a large variety of forest types. Ebony leaf monkey occur(red) in the small remnants of mangrove forests on the northern coast of West Java and East Java [7, 33], as well as in the larger mangrove and swamp area of Segara Anakan [15], on the south coast of Central Java. It occurs in forests along rivers and waterways and in the fresh water swamp forests [2]. In the western half of the island, it is widely distributed in the pockets of rain forest ranging from sealevel [1, 2, 5, 10] to the upper montane forests at 2,500 m a.s.l. and above [6, 17, 19]. In the eastern part of its range, it occurs both in the pockets of rain forest both at sea level [34] and on the eastern and southeastern slopes of the higher volcanoes [27, 28, 30, 41], in the fire resistant Cemara Casuarina junghuhni forests [26, 27, 32], as well as in the dry deciduous forests [33, 36, 38]. In the rain forest environment ebony leaf monkeys seem to be (almost) strictly arboreal, while in the more open forest types, e.g., dry decidious forest and upper montane forest, it seems to be more terrestrial.

The species is able to cope with a certain degree of habitat disturbance. It seems to survive in secondary forest types as well as some man-made forests such as damar Auracaria spp, pine Pinus merkusii, acacia Acacia spp, rasamala Altingia excelsa, rubber Hevea brasiliensis and teak plantations [2, 3, 13, 14, 17, 24, 26, 33]. Often, however, these plantations are situated adjacent to other more natural forest areas [e.g., 2, 13, 24, 33], while others are intersected e.g., by (river) valleys with a more diverse forest type [14, 17]. Typically, ebony leaf monkeys are found in or near these natural forest remnants. Alternatively some populations can be found ‘trapped’ in small fragments of (natural) forest, unable to move out as there is no adjacent forest left [e.g., 3, 20]. Although the species has been observed in a wide range of forest areas, generally it can be assumed that ebony leaf monkeys are dependent on natural forest in one form or another, and that large stands of monocultures offer little if any suitable habitat for the species.

FIG2

Pl. II. Melanic (foreground in cage) and erythristic pelage morph of ebony leaf monkey Trachypithecus auratus (E. Geoffroy Saint-Hilaire, 1812), Taman Topi, Bogor, West Java 1999. In Indonesia, many species of primates, including formaly protected species such as the ebony leaf monkey, are openly offered for sale, in this particular case in front of the police station. Note that the illegal primate trade includes transports over considerable distances as the nearest site where the erythristic pelage morph occurs [Mt. Penanggunang-Mt Arjuno] is more than 1000 km by road from Bogor.