Komodo dragons ( Varanus komodoensis ) on Rinca
|Ouwens , 1912|
The Komodowaran ( Komodo dragon ) or Komodo Dragon ( Varanus komodoensis ) is a lizard from the kind of lizards ( Varanus ), the distribution area of some of the small Sundainseln of Indonesia is limited. With a body length of a maximum of three meters and a weight of over 70 kg , it is the largest recent representative of the scale crawfish . The prey spectrum of the animals active during the day changes with age and increasing body size and ranges from insects to mammals such as red deer and wild boar . It is the only monitor lizard that regularly hits prey of this size. The hunt for large mammals is supported by a poison produced in specialized glands in the lower jaw , which among other things reduces blood clotting and causes a shock . Escaped prey can perish from this poison even days later. Also carrion is an important part of the food spectrum.
The Komodo dragons are the most important tourist attraction in their range , but are sometimes unpopular with the local population, as they occasionally kill farm animals . The Komodo dragon population is usually given as around 4,000 specimens, but it could have fallen below 3,000 in the meantime. The IUCN Red List of IUCN classifies the Komodo dragon as vulnerable (endangered) a.
Adult Komodo dragons have an almost uniformly earth-brown upper body, a grayish belly area and light yellow eyelids. Females can also have yellow-green, green-brown, pink or purple spots on the snout. Young animals, on the other hand, show a brown pattern with large yellow or orange spots on the back and on the snout. In young animals, the temple region has a grayish color interspersed with white spots. The front legs are brown with white spots, the belly is light yellow with some large dark spots. The juvenile markings gradually disappear with age: Subadult specimens still have a lighter color on the snout. This is especially true for the females, whose bodies, however, are already uniformly brown in subadult age. The iris is light brown in young animals, later brown. The tongue has a yellow color regardless of the age of the animal.
Adult Komodo dragons are massive, large lizards with a species-typical wide snout. Young animals are still quite delicately built, but in the course of their development they become more and more stocky, the hind legs become stockier and shorter and the slender tail proportionally increasingly shorter and thicker, until it is only about half the body length. The toes have relatively short, very sharp claws that curve backwards. Other special anatomical details are cutaneous bone plates under the scales on the front of the legs, at the base of the tail, around the neck and dorsally on the skull.
The dentition shows within the species a fairly constant number of slightly curved, pointed teeth that can be up to 2 cm long in very large individuals. The upper jaw has seven teeth on the front intermaxillary bone ( incisive ) and the paired upper jawbone ( maxillary ) adjoining it to the rear 13 teeth each. The lower jaw ( mandible ) has on both sides twelve teeth. Characteristically, the teeth of the maxillary have a line with 14 to 55 fine barbs on their rear edge.
The species shows a low sexual dimorphism : Males are usually somewhat larger and more massive than females and often have two depressions in the second and third row of scales in front of the cloaca , which are surrounded by small scales like a rosette.
Length and weight
Wild Komodo dragons reach sexual maturity regardless of gender with a total length of about 150 cm. Adult animals on Komodo have an average head-torso length of 92 cm with a total length of about 196 cm and an average weight of 23 kg, as shown in a study on the largest 15% of 226 individuals. On islands rich in prey, dominant individuals, especially males, also regularly reach overall lengths between 225 and 260 cm. Sporadically, the latter even achieve total lengths of around 300 cm. The largest male seriously measured so far comes from Loh Liang on Komodo and had a head-trunk length of 154 cm with a total length of 304 cm and a weight of 81.5 kg. The largest female comes from the Wae Wuul Reserve on Flores and had a head-to-trunk length of 135 cm with a total length of 267 cm and a weight of 42 kg. The longest measured specimen of the black tie monitor ( Varanus salvator ) exceeds the length of the Komodo dragon at 3.21 m, but the significantly heavier and stronger Komodo dragon is generally referred to as the largest recent lizard.
distribution and habitat
The Komodo dragon lives in Indonesia on the Lesser Sunda Islands : Komodo , Rinca , Gili Dasami , Gili Motang and in coastal areas in the north and west of the western part of the island of Flores . According to the local population, Komodo dragons also live in the northwest of West Flores and also on East Flores; however, these occurrences are not confirmed.
Komodo dragons can be found almost everywhere on the mountainous islands of Komodo and Rinca. They prefer to inhabit savannahs and seasonal monsoon forests , as well as grasslands, almost evergreen forests and sections of beach rich in vegetation. The population density is highest in the lowlands and is significantly lower around above sea level. Isolated individuals could even be detected on Komodo up to above sea level. On Gili Dasami, the species is mainly found in the seasonal green monsoon forests that are predominant there. On Gili Motang, monsoon forests also dominate the landscape, but the Komodo dragon also lives in savannahs in the coastal areas in the north and south-west. On Flores, the species also lives in a wide variety of vegetation forms, including in particular savannahs, grasslands, various dry to moist monsoon forest types and mangrove forests. In general, transition zones between denser and more open landscapes are important for Komodo dragons for optimal adaptation to daily climatic fluctuations and the seasonal climatic fluctuations caused by the long dry and short rainy periods. Overly open or dense and humid areas are avoided.
Way of life
Young Komodo dragons are excellent climbers and stay almost exclusively on trees. The main reasons are foraging, good hiding places, sunbathing areas and protection from large cannibalists. With increasing size, climbing becomes slower and more deliberate, but animals under 150 cm are still able to climb trunks vertically up to a height of 10 m. With a size of around 100 cm, they expand their activity space more and more to the ground and, from a total length of around 150 cm, switch to a ground-dwelling way of life. Adult Komodo dragons only live on the ground because their size and mass no longer allow them to climb. Komodo dragons are very active. Apart from digestive breaks, large individuals cover an average of 450 to 960 m daily, sometimes even up to 5.5 km at a speed of around 4.8 km / h. Movements of the Komodo dragon are strongly influenced by the search for partners in the mating season as well as carrion. In the event of danger, they can run at a speed of 14 to 18.5 km / h, pretty much regardless of their height, and maintain this speed for more than half a kilometer in an emergency. They are mediocre swimmers who move with their legs snuggled under water with undulating body movements and can sometimes dive up to 4 m deep. Unlike many monitor lizards, however, they rarely swim, mostly only over short distances, a maximum of about 450 m to the small islands off the mainland.
The species is diurnal from sunrise (at 6 a.m.) to sunset (at 7 p.m.). This pattern of activity remains essentially the same throughout the year, especially since Komodo dragons do not have a seasonal rest period. In the rainy season from January to March, activity is concentrated in the warmest hours of the day around noon. In the drier rest of the year, the animals warm up in the morning in the open from around 28 ° C to 40 ° C, rest in cool hiding places around hot midday and show increased activity in wooded areas from 1.30 p.m., and again around 5 p.m. in more open terrain. As a shelter during the hottest hours of the day and at night, adult Komodo dragons prefer one of their numerous, 0.75 to 3.2 m long and self-dug structures with their front legs, as well as caves of mammals or dense vegetation. Young animals hide in knotholes, tree hollows or under loose bark.
Komodo dragons are opportunistic hunters who locate their prey by flickering and rely on their visual sense at close range. Young animals feed primarily on small lizards and insects, which they actively track down under tree bark, and more rarely in the grass. Komodo dragons up to a total length of about 100 cm are also still active hunters, some of whom pursue their prey for up to 15 seconds. They prefer to eat rodents, which they dig up from their duct systems, as well as ground-dwelling birds and their eggs. Adult individuals mainly prey on large vertebrates, which preferably weigh half or as much, but regularly weigh twice as much as the monitor lizard itself. The most common prey animals are young maned deer and small wild boars , as well as macaques , feral dogs, domesticated goats, various poisonous and non-poisonous ones Snakes , sea turtles and their eggs, ground-dwelling birds and their eggs, calves of water buffalo and sambar and foals of feral domestic horses . Even prey animals over 100 kg are rarely attacked, and in unusual cases even water buffalo weighing up to 320 kg are overwhelmed. Furthermore, especially in places with a high population density, young conspecifics are also eaten ( cannibalism ).
Adult Komodo dragons hunt from ambush by lying in wait at the edge of deer passages, surprising their prey while they sleep, or slowly stalking their prey. From a distance of about 1 m, the prey is grabbed by suddenly rushing forward. Smaller prey animals are then crushed to death with their snouts on the ground, shaken to death or simply killed by a simple bite. Large prey is grabbed by the hind leg, buttocks or neck, wrestled to the ground by violent pulling and shaking, fixed, further deep wounds are bitten and the intestines torn out, which leads to bleeding to death. It usually takes 2.5 to 4 minutes from attack to death. The Achilles tendons of a very large prey are bitten through and gradually brought down and overwhelmed by further biting and pulling. Occasionally, such attacks fail, so that the injured prey flees and sometimes only dies from the poisoning days later.
In addition, semi-adult (adolescent) and adult Komodo dragons eat carrion whenever possible . You can perceive this by flickering at a distance of around 3 km, and under optimal conditions even from a distance of 11 km. The monitor lizard then follows the scent trail to the carcass. In rare cases, up to 17 individuals gather at larger prey. During such a feed aggregation, large individuals wait within a radius of about 1.5 m from the food resource until the animal above them in the hierarchy leaves the place saturated. Smaller individuals have to wait until they can get their move.
As with all monitor lizards, the prey is swallowed whole or in large chunks. Jerking the body back and forth and hitting the floor disarticulates bones and jerks the flesh with the sawed teeth. The prey is almost completely eaten, with larger carcasses only about 8%, with very large carcasses a maximum of 30% cannot be used. Komodo dragons can eat up to over 70% of their own body weight at mealtimes. For example, a 42 kg animal is able to cut up a 30 kg wild boar within 17 minutes and eat it almost completely. Digestion takes three to six days, parts that are difficult to digest such as hair, feathers, claws, hooves, teeth and larger bones are regurgitated in advance. The success rate of larger Komodo dragons in active hunting and carrion hunting is quite low, which is why they only come to a larger prey about once a month. Younger Komodo dragons, on the other hand, eat smaller meals more often and at more regular intervals.
Role of poison and bacteria in hunting behavior
The Komodo dragon has poison glands in the lower jaw, which consist of a clearly defined cavity ( lumen ) and passages that open between the teeth of the lower jaw into the oral cavity. As with all reptile poisons , the active components of the poison are a mixture of different proteins , with the Komodo dragon kallikrein , phospholipase A 2 (PLA 2 ), natriuretic peptides , proteins of the AVIT family and CRISP proteins. The poison causes unconsciousness through a rapid drop in blood pressure ( arterial hypotension ) and excessive sensitivity to pain ( hyperalgesia ) as well as inhibition of blood clotting ( coagulopathy ) with accelerated bleeding to death under volume shock . The poison optimizes the hunt, which may be the only way to overpower large prey. First biomechanical studies on the skull of the Komodo dragon indicate that the skull is essentially only well aligned when pulled from the front. In addition, the jaw has only a low bite force of 39 Newtons (N) ( saltwater crocodile with a comparable body size: 252 N). The initial poisonous bite can therefore compensate for the skull's lack of resilience and make it easier for the prey to be brought down. In comparison, other large predators such as big cats have much more resilient skulls for attacking large prey.
It used to be assumed that larger, bitten prey would die of bacterial sepsis (blood poisoning) days later after a failed attack . In fact, various pathogenic bacteria are found in the Komodo dragon's saliva , which can cause death from sepsis over time. It is assumed, however, that these bacteria usually play a subordinate role in the death of escaped prey and that the main reason for the rather rapid death is to be ascribed to the effect of the applied poison.
Poison glands are not limited to the Komodo dragon in the "lizards" ( scaled reptiles , exclusive snakes (Serpentes)), but are likely to be found in all monitor lizards and all members of the taxon Toxicofera , to which the monitor lizards also belong. As with all monitor lizards, it also seems likely with the Komodo dragon that the poison with components such as PLA 2 also supports digestion.
Social behavior and spaces for action
Komodo dragons are primarily solitary animals. Dominant individuals claim 258 to 529 hectares of territories that have been retained for years and which they mark with excrement. The territories of the monitor lizards can be divided into a small core area and a large grazing area. Around half of all activities take place in the core area with the preferred sunbathing areas, hiding spots and the most important prey trails. In the also very familiar roaming area, breeding sites, wild animal trails and sleeping areas are searched for potential prey on numerous routes at regular intervals. In addition, dominant Komodo dragons have a much larger area that is more difficult to quantify, which they use to find animal carcasses. In contrast to core areas, grazing areas are not specifically defended and in dominant males overlap on average 35% with the grazing areas of other males and up to 99% with those of females. Young and younger adult animals are migrants, move very carefully over other areas according to rather random patterns and seem to have no territory of their own. These movements could play an important role in population genetics .
The intra-species communication of the Komodo dragons is very well developed for lizards. If several individuals come together at a food resource, if they meet by chance or if they compete for reproductive partners during the mating season, they show different expressive behavior in order to establish a hierarchical relationship. Visual signals are primarily used for this. Threatening gestures include raising the head in increasing levels, spreading the throat vertically, hissing, bringing the tail into a whipping position, opening the mouth, running towards the opponent and biting. Submission is signaled by lowering the head and high-legged in a stiff step, pressing the body on the floor and stretching legs or by running away. Usually the dominant animal gives the inferior a chance to escape. When several animals gather around a food resource, conspecifics are tolerated if they fit into the hierarchical system.
Reproduction and development
The Komodo dragon's courtship and mating season lasts from May to August, but occasionally matings are observed outside of the actual season. Often the sexes meet by chance on a carcass. However, the males often cover long distances when looking for a partner. If the hierarchy among the males is not yet regulated when several monitor lizards ready to mate, these ritualized fights for the females, so-called comment fights, take place . With the Komodo dragon, these are “waran-typical”: the opponents stand up facing each other on their hind legs, support themselves with their tails, grab the opponent's upper body with their front legs and try to bring the opponent down. The winner will have access to one or more females. Females are courted by first flicking them from the tip of the snout to the cloaca. Then the male rubs his head on the female, presses his snout onto the base of her tail, scratches her back with his forelegs, and finally the male rises on her back to mate. During the first phase of courtship, females often show defensive behavior, threaten or bite and tear themselves away, which is why mating usually only succeeds after several attempts.
In the dry season, usually in September, the females lay clutches of a maximum of 33, on average 18 leathery eggs, which are on average 87 × 56 millimeters in size and weigh 125 grams. They are preferred to be buried in brood mounds up to 1.5 meters high that have already been created by large foot fowl. In addition, self-dug nesting trays are also used. Often the eggs of a clutch are spread over several nests in order to increase the chances of survival from nest predators. Females were also observed who visited their clutch at regular intervals or who guarded it almost permanently for three months. The young finally hatch after a very long incubation period of around eight months at the end of the rainy season from March to April. When hatched, they are on average 42 cm long and weigh 100 g. In the first year of life, the young grow to almost double their birth length, after which the speed of growth decreases steadily. Compared to other monitor lizards, Komodo dragons become sexually mature relatively late. In captivity, both male and female animals reach sexual maturity at five years of age at the earliest. The respective age is estimated at around nine years for wild females and ten years for males. It is believed that it usually takes an animal over eleven years to grow to be over two meters in length.
At least two confirmed cases of parthenogenesis of Komodo dragons are known from zoos . Parthenogenesis is the ability of a female animal to give birth to viable young without prior fertilization by a male. With Komodo dragons and other monitor lizards there is also the special feature that in parthenogenetically generated clutches there are only males instead of the usual females. This is related to the ZW system in reptiles: when the female passes on two Z chromosomes , males develop. A young animal with two W chromosomes is not capable of development.
Natural enemies and life expectancy
Larger Komodo dragons have no predators, but young animals are hunted not only by their larger conspecifics but also by feral dogs, civets , wild boars, birds of prey and snakes. Wild Komodo dragons are mainly parasitized by the tick Amblyomma robinosoni , but also by Aponomma komodoense and Amblyomma helvolum . The ticks are usually found on the back and on the flanks, especially above the lateral fold and at the base of the legs. The number of ticks is greatest during the height of the dry season and decreases sharply after the onset of the rainy season. As endoparasites are amoebas of the genus Endolimax and tapeworms of the genera Duthiersa and Acanthotaenia .
Information on the average and maximum ages of individuals living in the wild is unknown. The maximum life expectancy is estimated to be at least 30 years. In the Taronga Zoo in Sydney , a copy was 24 years old.
It was first described in 1912 by Pieter Ouwens , then director of the zoological collection of Bogor (Java). Ouwens used the skin of an adult specimen as a holotype and published photographs as additional evidence. Based on its hemipenis morphology , the Komodo dragon is placed within the genus Varanus in the subgenus Varanus . According to DNA analyzes, Varanus varius is the sister species of Varanus komodoensis . The two species together form the sister taxon of Varanus salvadorii and all three species together form the V. varius group within the Indo-Australian monitor lizards. Sister group of the V. varius group are the small monitor lizards of the subgenus Odatria . Although noticeable genetic differences have been found in the Komodo dragon's distribution area, no subspecies is currently recognized on either a morphological or genetic basis .
Initially it was assumed that the enormous body size of the Komodo dragon had developed after the immigration of a smaller species of monitor lizard to the Lesser Sunda Islands due to island gigantism , perhaps also as an adaptation to the hunt for the now extinct dwarf elephant of the genus Stegodon . According to today's molecular biological and paleobiogeographical findings, the Komodo dragon is part of an Indo-Australian clade of large monitor lizards, which developed their enormous size already during the Pliocene in Australia and which also contained the largest monitor lizard ( Varanus priscus , died out after the Pleistocene ). The Komodo dragon evolved in Australia in the early Pliocene. The fact that sea levels often fell during the last ice ages would have favored further expansion to the southwest in the Indonesian archipelago. The Komodo dragon reached Flores about 900,000 years ago, occurrences at this time are proven by fossil teeth. He probably settled Java 800,000 to 700,000 years ago. It eventually died out, except for the area where it is distributed today. The Komodo dragon can therefore be regarded as the last survivor of an Australian radiation of large monitor lizards.
Existence and endangerment
The IUCN classifies the Komodo dragon since 1996 in the Red List of Threatened Species as endangered ( vulnerable ) a, 2004, however, the proposal has already been made, threatened him as strong ( endangered each). Inventory estimates from 2002 assume around 2000 specimens on Flores, 1700 specimens on Komodo, 1300 specimens on Rinca and 100 each on Gili Motang and Gili Dasami, but the population on Flores may have dropped to 500 by now. The main threats for the Komodo dragon are currently habitat fragmentation and, above all, the decline in the populations of mane deer , wild boar and water buffalo , the most important prey for large monitor lizards. Poaching , fires (partly caused by humans) and clearing, the latter both mainly to gain new arable land, are responsible for the decline . On Gili Motang, the effects of the decline in prey animals were examined in more detail: It was found that the Komodo dragons there remained significantly smaller compared to other populations due to lack of prey, and in 2004 the catch rate of monitor lizards in traps with bait was 63.56% lower than in 1994 The extinction of the Komodo dragon on Padar (also Lesser Sunda Islands) in the late 1970s is also likely due to a lack of larger ungulates. In addition, Komodo dragons often have to compete for carrion with feral domestic dogs.
In 1980 the Komodo National Park was founded to protect the Komodo dragon , later the Wae Wuul Reserve was established in the west of Flores and the Wolo Tado Reserve in the north . The animals are strictly protected in Indonesia. The Washington Convention on Endangered Species lists the Komodo dragon in Appendix I, so any trade in live Komodo dragons or parts of their bodies (e.g. skins) is prohibited without special permits. In Komodo National Park, rangers try to stop poaching, which is partly responsible for the decline in prey. Conservation breeding in captivity can also serve to preserve the species. The first offspring in human care outside their native Indonesia took place in 1992 in the Smithsonian National Zoological Park . The first European offspring succeeded in 2004 in a zoo on Gran Canaria .
Komodo dragons and humans
Behavior towards people
Komodo dragons avoid confrontation with humans. Young animals are shy and sometimes flee quickly to a hiding place at a distance of 100 m when a person approaches. Older animals only retreat in a slow trot at a shorter distance. When Komodo dragons are cornered, however, they react aggressively, opening their mouths, hissing warningly and bringing their tail into a whipping position. If the attacker does not let go, they counterattack by running towards the enemy and finally trying to bite him. There are some reports that Komodo dragons allegedly attacked humans or, in individual cases, even killed and ate them. Of the few seriously verifiable reports, most attacks have been shown to be defensive bites of human threat. Only a few incidents were demonstrably unprovoked. Auffenberg (1981) believes that these attacks can only be traced back to a few abnormal individuals who have lost their fear of people and are unusually aggressive.
In captivity, Komodo dragons can become tame, recognize their keepers and sometimes show play behavior . Like all monitor lizards, they are considered comparatively intelligent.
Relationship with the local population
Komodo dragons are sometimes very unpopular with the local population because they occasionally kill farm animals (especially goats) and eat fish that are hung up or laid out to dry. Komodo dragons are also believed to have dug up freshly buried dead bodies and ate the corpses. On the other hand, as a major tourist attraction , Komodo dragons are an important source of income for the inhabitants of the Lesser Sunda Islands. In 1995/96 monitor lizard tourists spent an estimated $ 1,100,000 partly in the Komodo National Park itself, but for the most part in the two places from which it can be reached; the income from tourism is very important to the population.
In 2018 the local government decided to keep Komodo Island closed to tourists in 2020. Then new trees should be planted and the monitor population should recover. In addition, the entry fees are to be increased significantly.
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