San Francisco State University
The Biogeography of the Komodo Dragon
by Craig Jung, student in Geography 316, Spring 1999
photo source: Ciofi 1999
Species: V. komodoensis
Description of Species:
In Indonesia there is a type of lizard that can reach sizes that you may have thought only existed in fairy tales. These unique reptiles have been able to develop in an area where there is little for large animals to live on. They were there long before humans but like many organisms around the world they are subject to the growing human populations. These monitor lizards are known as Komodo dragons.
The Komodo dragon, also known as Varanus komodoensis, may reach lengths of up to three meters and may weigh as much as 500 pounds. They have claws that may be as long as ten centimeters, teeth that operate like little scalpels and saliva that contains a deadly bacteria, staphylococcus (Cherrington, 1997). These monitors are known to be strong swimmers and may dive down to depths of 15 feet. Most importantly they possess great intelligence, displayed best when they hunt or search out their next meal.
These unique animals are only found on the island of Komodo and three nearby islands in Indonesia. These islands are located in the lesser Sunda, halfway along the Indonesia archipelago, east of Bali and west of Timor. Human populations are small on these three islands. The island of Komodo contains about 1,700 dragons, Rinca has 1,300, and the tiny island of Gili Motang possesses around 100 dragons. Komodo National Park consists of these three islands and various other islets. Around 2000 more Komodos live on the island of Flores located to the east (Ciofi, 1999).
Komodo dragons are one of the largest carnivorous reptiles. These large lizards start out as hatchlings only a foot long. Young dragons live in the trees for protection from larger predators and adult Komodo monitors. Their diets consist of insects and small lizards. When they reach adolescence their diets may consist of rodents, birds, and large mammals occasionally. Adult Komodo dragons can take down large animals fifteen times their size, like water buffalo (Cherrington 1997). When large mammals are not available adult monitors will scavenge or eat rodents. Monitors tend to rely on the element of surprise in order to catch a meal. They will lie and wait in heavy brush waiting for some unsuspecting deer or wild boar to cross their path.
Large prey usually will be struck at the ankles causing them to fall to the ground where they will be finished off by the monitor's powerful jaws. Their deadly saliva causes serious infections with no known cure. Even if the prey manages to escape the initial strike, they inevitably will die from an infection or bleed to death . These large monitors are rather fast for their size, 11 m.p.h., but only for short distances. Adult dragons have voracious appetites and can eat up to 80% of their empty body weight (Diamond 1992). They will eat everything from the bones to the hooves. Yet a 100 pound adult can survive on only 30 pounds of meat a month when it becomes necessary (Diamond, 1992). Their diets today, water buffalo and deer, were introduced by humans.
No distinguishing physical features provide any indications in determining their gender. Males tend to be larger than females but other than that there are no striking morphological differences. One slight difference lies in the arrangement of their scales in front of their cloaca, the cavity that contains their genitalia (Ciofi, 1999). Regardless of our inability to determine the proper gender, Komodo dragons know who is who and what is what. They tend to mate between May and August. Before mating occurs the dominant males battle to determine who will be their mate. They do not fight to the death, but blood is usually drawn. Their tails play an integral part during battle as they get in upright positions and wrestle (Ciofi, 1999). The winner of the wrestling match gets to choose his mate.
Courtship begins with the male flicking his tongue on the female's nose and then over her body. The male must expose a pair of hemipenes from his cloaca before mating can be accomplished. Once this has happened he then climbs on the back of his mate and inserts one of the two hemipenes into the female's cloaca (Ciofi, 1999).
A couple of months after the hot season female dragons will lay their eggs in September. Cooler conditions provide a better environment for the developing eggs. Usually the female monitor will dig out an area on a hill or takeover the nest of a Megapode bird (Ciofi, 1999). During the incubation period she will lie on the nest and protect her future offspring. Once the young hatch the female will tend to the young alone which is common for Komodos.
They share a common past with dinosaurs but are not direct descendants. Both dinosaurs and monitor lizards belong to the subclass Diapsida (Ciofi, 1999). The earliest fossils from this subclass go back to the late Carboniferous period, about 300 million years ago. Monitor lizards are related to Lepidsauria which emerged from Diapsida, about 250 million years ago at the end of the Paleozoic era. About 100 million years ago, during the Cretaceous era, a species related to contemporary varanids appear in the fossil records of central Asia. Marine lizards from this species went extinct, along with dinosaurs, about 65 million years ago. During the Eocene, 50 million years ago, land monitors spread throughout Europe and South Asia. The Varanus genus appeared and evolved about 40 and 25 million years ago in Asia. Varanids made it to Australia about 15 million years ago when Australia collided with southeast Asia. Then 2 million years later a second lineage differentiated and moved throughout Australia and the Indonesian archipelago when the two were much closer. Lower sea levels allowed the dragons to reach their destination. Varanus komodoensis differentiated from its earliest Australian relative about 4 million years ago (Ciofi, 1999). Komodos migrated to the islands of Flores, Rinca and Gila Motang, which were joined about 10,000 years ago. The island of Komodo joined the other islands around 20,000 years ago during the last Ice Age.
Fossil evidence supports the idea that Komodo dragons may be relics of a larger distribution, stretching as far as the eastern portion of Flores to Timor. Fossils from pygmy elephants, stegodont, found on both Timor and Flores suggest that the two islands may have been close enough to allow migration during the Pleistocene era. The existence of large mammals provided an adequate supply of food to feed lizards as large as Komodo dragons and possibly larger. Megalania prisca, a varanid, could have reached lengths up to 23 feet and weighed up to a ton due to the existence of stegodonts or pygmy elephants (Diamond, 1992). These enormous varanids, that have been extinct for 25,000 years, may explain how Komodo dragons evolved to be such large carnivores in an ecosystem that has a limited amount of resources.
There are two routes they could have traveled to reach their present location. They either arrived directly from Asia or came through the island of Java or Australia. The Komodo dragons are endemic to the islands of the Lesser Sunda. Their biomes consist of savanna, tropical scrub forest, and tropical grasslands. They managed to fill a niche on the islands which allowed them to evolve into modern day dragons. Komodo monitors colonized these small islands due to their cold blooded body types, and the conditions of the islands. The island of Komodo falls within the rain shadow of the larger island of Sumbawa (Cherrington, 1997). Komodos are known to go about a month and a half without water in the dry season. As reptiles, Komodo monitors do not require as much energy or food as carnivorous mammals, like tigers. Warm-blooded animals tend to have higher metabolisms that may limit their range to areas with sufficient food supplies. Cold-blooded animals require only one-tenth as much food as a mammal the same size (Diamond, 1992).
Map of Distribution:
Map Source: Ciofi 1999
Other interesting issues:
Deer poaching has created problems for some of the lizards to the point were they have been put on the endangered species list. Poaching combined with human interactions make the Komodo's situation worse. The island of Flores has both of these problems for the monitors. Slash and burn is practiced in the monsoon forest leading to the disappearance of the dragons (Ciofi, 1999). Once again humans are at the heart of some serious environmental problem. The fate of the Komodo dragon lies in the hands of people. Our choices will effect how another species will live or die. Hopefully we will all see the importance of such a rare reptilian species.
A new web site by Tim Spaulding is devoted to komodo dragons. You may want to check it out at http://www.isidore-of-seville.com/komodo/ .
Cherrington, Mark. 1997. "Here Be Dragons." Earthwatch
Ciofi, Claudio. 1999. "The Komodo Dragon." Scientific America 280(3): 84-91. Maps of the
Lesser Sunda came from the web site:www.sciam.com/1990/0399issue/0399ciofi.htm
Claudio Ciofi's article provided valuable information concerning the evolutionary history of Varanids.
Diamond, Jared. 1992. "The Evolution of Dragons." Discover 13(12): 72-80.
Quammen, David. 1996. The Song of the Dodo: Island Biogeography in an Age of Extinctions. New York, NY. Scribner.
Stevens, Jane. 1993. "Facing The Dragon." International Wildlife 23(3): 30-34.
Winters, Chris. 1995. Varanus komodoensis. University of Michigan [online] http://www.http.itd.umich.edu/bio /doc.cgi ...uamata/Varanidae/Varanus_komodoensis.
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