Gray's monitor lizard
| Gray's monitor lizard | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
Gray's monitor lizard ( Varanus olivaceus ) |
||||||||||||
| Systematics | ||||||||||||
|
||||||||||||
| Scientific name | ||||||||||||
| Varanus olivaceus | ||||||||||||
| Hallowell , 1857 |
Gray's monitor lizard ( Varanus olivaceus ) is a species of scale reptiles (Squamata) from the genus of monitor lizards ( Varanus ). The species, which is quite large with a total length of up to 2 m, lives in the rainforests of the Philippines , is tree-dwelling and, in contrast to the other, mostly carnivorous monitor lizards, feeds mostly on fruits. The IUCN classifies Gray's monitor lizard as endangered.
features
In terms of size and weight, Gray's monitor lizard shows a clear sexual dimorphism . Large males reach total lengths of up to 2 m and weigh 9 kg. On average, males reach head-torso lengths of 65 cm with a weight of 6.7 kg, females KRL of around 50 cm with a weight of 2.6 kg. The head is proportionally large, the nostrils are in the middle between the eyes and the tip of the snout. The hind legs are longer than the front legs and very large for monitor lizards. The belly scales are keeled and provide additional support when climbing. Two keeled rows of scales on the top of the tail, which is compressed to one side, form a low crest.
The basic color of the monitor lizard is greenish-gray, on the neck, back and tail there are some dark, intersecting bands. This pattern is more pronounced in young animals than in old animals. The legs are colored darker than the body: They are gray-brown to black-brown and marked with slightly lighter spots. The feet are dark brown to black and have gray, green or yellow spots. The claws are black, large, strongly curved and are used for climbing.
The basic color of the young is clearly lighter and yellowish.
distribution and habitat
Gray's monitor lizard inhabits the east of the Philippine island of Luzon as well as the smaller islands of Catanduanes and the Polillo archipelago . It lives on the densely forested mountain slopes of these islands and occurs at up to 400 m above sea level.
Way of life
behavior
Like all monitor lizards, Gray's monitor lizard is diurnal. Since it lives at 14 ° N near the equator, the climate in its habitat is fairly constant, and the monitor lizard is equally active all year round. The species rarely basks in the sun and is a rather passive thermoregulator . The body temperature is usually between 28 and 38 ° C. To protect against enemies, these monitor lizards rely on their color pattern, which camouflages them in the rainforest. Gray's monitor lizard has only very small action spaces .
He is a tree dweller and only leaves the trees to eat.
nutrition
Adult grays monitor lizards are mainly fruit-eaters ( frugivores ), but also eat snails and crabs. They eat ripe fruit that has fallen to the ground as well as fruit that is still hanging on the trees and are very picky. Oily fruits are particularly preferred. The availability of the fruits depends strongly on the season: sweet fruits are available from May to July, oily fruits from February to March and from August to November. The monitor lizards apparently remember the location of individual trees and return to these trees year after year when they bear ripe fruit. Between November and January, at the height of the rainy season, very little fruit is available - then snails, crabs, spiders, beetles and grasshoppers, and occasionally bird eggs and small birds, make up a larger proportion of the diet. In adaptation to this mostly hard-shelled prey, Gray's monitor lizard has developed blunt teeth, a particularly long intestine and an appendix with symbiotic bacteria to better develop the fruit food . Such characteristics are also found in other fruit-eating, closely related monitor lizards such as the Panay monitor lizard ; Compared to these, Gray's monitor lizard feeds more on animal food.
Since these monitor lizards are the largest fruit-eaters in Southeast Asia, they could play an important role in the spread of seeds.
Reproduction
The ritualized commentary fights typical of monitor lizards take place from April to June, the pairings from June to September. Courtship and mating behavior is complex and heavily ritualized. The fairly large eggs, which make up 18.6% of the body weight of highly pregnant females, are laid between July and October in hollow tree trunks and tree hollows of standing and fallen trees. Although up to 2 eggs per year were laid in captivity, in nature a female should only produce one clutch per year. The clutch consists of 4–11, on average 7 eggs. After a long incubation period of up to 300 days, the young hatch between May and July, i.e. during the next rainy season.
The teeth of the young animals are still pointy and sharp, they mainly feed on animal food. The young are around 35 cm long when hatched and weigh 25 g. They reach sexual maturity after about 3 years with a head-trunk length of 45 cm.
Systematics
The nomenclature of this kind has been quite agitated. It was first described in 1845 by the well-known British zoologist John Edward Gray , who described this species as Varanus ornatus using a young animal from the Philippines . In 1885, George Albert Boulenger recognized that this scientific name had already been assigned to the rainforest Nile monitor by François-Marie Daudin in 1803 , so Gray's name was not valid according to the priority rule. Boulenger suggested naming Gray's monitor lizard Varanus grayi - but the US zoologist Walter Auffenberg discovered in the 20th century that Edward Hallowell had named another specimen of Gray's monitor lizard as Varanus olivaceus as early as 1857 . This name has priority over all others and is valid.
Within the genus Varanus , Gray's monitor lizard is placed in the subgenus Philippinosaurus together with the Panay monitor lizard ( Varanus mabitang ) and Varanus bitatawa - all three species inhabit the Philippines and feed largely on fruits. The current internal systematics of Varanus is based largely on the hemipenis morphology , in which the three species mentioned show clear similarities.
Existence and endangerment
Gray's monitor lizard is one of the most threatened monitor lizards and is classified in the IUCN's Red List of Endangered Species as vulnerable . Exact population estimates are not available, but the population density is estimated to be low in the very small distribution area. The main threats are habitat destruction, habitat fragmentation and hunting for food. Locals prefer Gray's monitor lizard to other monitor lizards because the meat of Gray's monitor lizard is said to be healthier, better tasting and smelling more pleasant. Young or adolescent animals are also caught alive for the international pet trade. For all these reasons, the stock is falling. The Polillo Butaan Project is currently being operated to protect Gray's monitor lizard ; the monitor lizard also inhabits some protected areas. Nevertheless, further protected areas would have to be established in order to prevent clearing to gain arable land and to secure the existence of the species.
literature
- Eric R. Pianka: Varanus olivaceus. In: Eric R. Pianka, DR King (Ed.): Varanoid Lizards of the World. Indiana University Press, Bloomington / Indianapolis 2004, ISBN 0-25334-366-6 , pp. 220-224.
Web links
- Varanus olivaceus in The Reptile Database
- Varanus olivaceus onthe IUCN Red List of Threatened Species 2010.
- Pictures and reports on the current situation on the Polillo Project website
Individual evidence
- ↑ a b c Varanus olivaceus in the endangered Red List species the IUCN 2010. Posted by: E. Sy, L. Afuang, MR Duya, M. Diesmos, 2007. Accessed 29 January 2011..
- ^ A b D. Bennett, K. Hampson: Further Observations of Varanus olivaceus on the Polillo Islands. Report of the Polillo Butaan Project 2001. Full text (PDF; 20 kB)
- ^ A b M. Gaulke, AV Altenbach, A. Demegillo & U. Struck (2007): On the Diet of Varanus mabitang. Mertensiella 16 ( Advances in Monitor Research III ), pp. 228-239.
- ↑ H. Godínez-Álvarez (2004): Pollination and seed dispersal by lizards: a review. Revista Chilena de Historia Natural 77, pp. 569-577.
- ↑ LJ Welton u. a. (2010): A spectacular new Philippine monitor lizard reveals a hidden biogeographic boundary and a novel flagship species for conservation. Biology Letters 6 (5), pp. 654-658.
- ↑ T. Ziegler, M. Gaulke, W. Böhme (2005): Genital Morphology and Systematics of Varanus mabitang Gaulke & Curio, 2001 (Squamata: Varanidae). Current Herpetology 24 (1), pp. 13-17.
- ^ MAP Reyes, D. Bennett, C. Oliveros (2001): The Monitor Lizards of Camaguin Island, Northern Philippines. Full text (PDF; 197 kB)