Dispersal To The Indonesian Islands Biology Essay


The Varanus Komodoensis, commonly referred to as the Komodo Dragon is a species found on the Indonesian islands. These islands include: Komodo Island, West Flores, Rintja (most reside on these three islands), Padar, and Nusa Mbarapu. They are also found on islands near Indonesia including the lesser Sunda, Bali and West Timor (Quammen 137). They are endemic to most of these islands. There are about 3,000-5,000 V. Komodoensis' on the Earth (Harlow et al. 339). V. Komodoensis is important to maintain population control within their islands. Varanids, commonly known as monitor lizards, first appeared in southeast Asia, and then Australia when the two continents collided about fifteen million years ago. The V. Komodoensis was then thought to evolve and colonize on Indonesia, when Australia and Indonesia were closer than they are today due to continental drift (Auffenberg 77-80). The V. Komodoensis can tolerate biomes of tropical savannah forests, open lowland habitat, beaches, and dry riverbeds (ibid 15). The restricted range of the V. Komodoensis, the largest carnivore to be so restricted, is still a topic of debate. This and their dispersal and range on the Indonesian (and surrounded islands) will be discussed in this paper.

Dispersal to the Indonesian Islands

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The Varanids genus first appeared in Asia at least 90 million years ago when the dinosaur era was ending. This genus then continued to colonize South East Asia and eventually made their way to Australia (Pianka 402). This was possible because they travelled to Australia before continental drift separated these two continents further apart than they were fifteen million years ago. About two million years later, it is thought that a second lineage spread through Indonesia, which included the V. Komodoensis. Like the previous colonization between Asia and Australia, Indonesian islands and Australia were thought to have come into contact during the Miocene thus closer together at the time making this transition to the islands possible (shorter distance to travel) (Auffenberg 45-46). It is also thought that the lineage formed in Indonesia when sea levels were low, thus making it possible for them to swim and colonize the islands, which were also closer together before drifting apart. Furthermore, the sea levels were thought to rise up again after this travel from Australia thus isolating the species to the islands and accounting for their low dispersal rates throughout the world (ibid.). The large size of the V. Komodoensis was thought to be due in part to their evolutionary history of large varanids (Pianka 401) but primarily to their lack of predators, making them an apex species, and their status as a "specialist hunter" of the pygmy elephants in which a large size would be necessary in hunting such a large species (Stegodon) (ibid 39).

Disputing claims of arrival to Indonesian islands

While the notion is that the second lineage of Varanus species, including the V. Komodoensis, evolved in Indonesia, this notion was disputed by a team of Australian scientists, led by palaeontologist Scott Hocknull. Hocknull argued that the V. Komodoensis actually attained its gigantism from its evolutionary traits (Meiri et al. 96) passed down from V. salvadorii, V. varius and Varanus prisca. Thus the morphology of the V. Komodoensis is not usual to its genus; rather it was passed down its evolutionary tree (Hocknull 1-2). The scientists also argued that the V. Komodoensis actually evolved in Australia before travelling to Indonesia. The study indicates that "the fossil record suggests that giant varanids evolved independently on mainland Asia and the island-continent of Australia during the Pliocene. This is because many fossils were found on Australia that appeared to be identical to V. Komodoensis in size and make up. They appear to have evolved along with many other large lizards around 3-4 million years ago (ibid. 10).

This conflicting information may be due to the fact that the V. Komodoensis was not discovered until 1910. Their isolation made it difficult to be studied prior to this time, so the research about their history is relatively limited.

Distribution on the Indonesian Islands

Before the Indonesian islands and surrounding islands experienced drift, they were fairly close together, if not attached. At this time the V. Komodoensis were able to disperse across the land, which then turned into various islands. The V. Komodoensis can tolerate biomes of tropical savannah forests, open lowland habitat, beaches, dry riverbeds. Indonesian islands tend to be tropical and hot, thus suited for the V. Komodoensis (Auffenberg 15). Younger komodo dragons stay in trees to avoid predation from older komodo dragons that eat young dragons. As they grow older they go to ground level and hunt for larger mammals (Jessop et al. 465). Since V. Komodoensis eat almost any species, including their own, they can be found on any part of the island looking for food. A map of the dragons' nests can indicate where they are usually found, as seen in Figure 1 (Jessop et al. 465).

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Figure 1 Black dots indicate nests of V. Komodoensis throughout Komodo National Park on Komodo Island (Jessop et al. 465). Movement and foraging mostly occurs during rainy seasons when it is less humid and the weaker preys are out (i.e. small lizards, rats, deer). They occupy the entire island of Komodo and certain areas of the other islands (i.e. they occupy 400 square kilometres of Flores). The V. Komodoensis can tolerate temperatures ranging from 65-107 degrees Fahrenheit (Harlow et al. 3).

Survival mechanisms

The endemism of the V. Komodoensis is due to its isolation and stability (Cox and Moore 90). The V. Komodoensis is an apex predator. They have essentially no living threats on the islands. This may account for their ability to maintain their large size and ability to survive despite such low distribution (Meiri et al. 90). Poaching and natural disasters are essentially the only threats of extinction of the species. They are responsible for population control of herbivores in their habitat. Without the V. Komdoensis, the herbivores they eat would dominate the ecosystem, who would in turn eat up all the plant life and cause extinction to the plants on the islands. The V. Komodoensis' ability to hunt and kill makes it extremely prone to survival. They also have a slow metabolism so they can go without eating for weeks. Their ability to regulate their body temperature by sitting in the sun if they are cold, or seek shade in order to cool themselves down allows them to tolerate the conditions of the islands at any time of year (Harlow et al. 340). V. Komodoensis' are also excellent swimmers so they can swim short distances to the various islands that they inhabit for various reasons, i.e. food, temperature preference, etc. These reasons all explain their endemism and their adaptability to such a limited distribution of only a few isolated islands (Auffenberg 126).


The V. Komodoensis is very limited in distribution. They are found on Indonesian islands and the surrounding ones (Quammen 137). Their ability to effectively hunt and tolerate the conditions that they live in, year round, makes them likely to survive for a long time despite their low population. Explanations for their isolation include their migration to the Indonesian islands early on and the rising sea levels once they already arrived there (Pianka 402). There has been controversy about their evolution occurred. It has been commonly accepted that they evolved, through a second lineage, on the Indonesian islands. However a study led by Scott Hocknull found that they might have actually evolved on Australia, alongside other Varnsus', before arriving to the islands (Hocknull 1-2). There is also no clear answer regarding their limited distribution to only select islands. V. Komodoensis were discovered relatively late in human history (1910) which may explain the elusiveness about their evolution and their limited distribution, despite their large size. The V. Komodoensis are limited in number but because of their status of an apex predator, biome tolerance and government protection (from poaching, selling skin), they should continue to thrive.


Auffenberg, Walter. The Behavioral Ecology of the Komodo Monitor. Gainesville: Universityes of Florida, 1981.

Cox, Christopher Barry, and Peter D. Moore. Biogeography: An Ecological and Evolutionary Approach 7th ed.. Oxford: Blackwell Publishing, 2005.

Harlow, Henry J., Deni Purwandana, Tim S. Jessop, and John A. Phillips. "Size-Related Differences in the Thermoregulatory Habits of Free-Ranging Komodo Dragons." International Journal of Zoology 2010 (2010): 1-9.

Hocknull, Scott, Philip J. Piper, Gert D. Van Den Bergh, and Rokus Awe Due. "Dragon's Paradise Lost: Palaeobiogeography, Evolution and Extinction of the Largest-Ever Terrestrial Lizards." PLOS One 4.9 (2009): 1-15.

Jessop, T., and Joanna Sumner. "Distribution, Use and Selection of Nest Type by Komodo Dragons." Biological Conservation 117.5 (2004): 463-70.

Meiri, Shai, Pasquale Raia, and Albert B. Phillimore. "Slaying Dragons: Limited Evidence for Unusual Body Size Evolution on Islands." Journal of Biogeography (2010): 89-100.

Pianka, Eric R. "Evolution of Body Size: Varanid Lizards as a Model System." The American Naturalist 146.3 (1995): 398-414.

Quammen, David. The Song of the Dodo: Island Biogeography in an Age of Extinctions. New York: Simon & Schuster, 1997.