Archive for the ‘lizards’ Category

How did Komodo dragons survive?

dragon eats goat

Komodo dragons are the world’s largest lizard.  They are supersized monitor lizards that first evolved in Australia four million years ago.  One million years ago they arrived on the Wallacea Islands, where they fed upon a dwarf species of elephant. That elephant went extinct 50,000 years ago. The mainland Australian population of these lizards went extinct around the same time as those dwarf elephants.  The main prey of Komodo dragons now consists of introduced ungulates that arrived on those islands between 7,000 and 10,000 years ago.

That means Komodo dragons spent 40,000-43,000 years without large terrestrial prey sources, and if that is the case, how did they survive?

Well, a new paper in the journal Global Ecology and Conservation attempts to answer that question.

Apparently, Komodo dragons are an odd mix of the best ectotherms and the best of endotherms.  As ecotherms, they have the ability to rely upon limited food resources, and it just so happens that the oceans around their last island redoubts are quite diverse marine ecosystems. So the dragons would have plenty of marine food that they could scavenge. They also have the ability to reduce their growth rates to compensate for the lack of large prey species on the island, a trait that has been shown in the subfossil record. Remains of dragons that date to these lean millennia show that dragons were significantly smaller then than they are now.

Also, unlike most ectotherms, Komodo dragons, like virtually all monitor lizards, have the ability to adjust their behavior and try new food sources. When tourists scared off the ungulate prey of Rinca Island, the dragons simply started hunting macaques and raiding scrubfowl nests.

Further, the dragons could also live nicely as cannibals. Smaller dragons get eaten by the larger ones, and because the dragons produce far more offspring than could ever reproduce, the excess dragon young could have fed the adults quite well.

Humans also never really thought of these arid and semi-arid islands as good places to set up large scale agriculture, and because these islands were also devoid of native prey species, humans were not widely using them as places to hunt until deer, buffalo, and pigs were introduced.  When humans did settle the islands, there were enough dragons in the population that had “shy personalities” that kept them from causing conflicts with humans. These “shy” dragons are disproportionately female, and they could have passed these more retiring traits onto their offspring, which is why Komodo dragons are not killing people left and right. People likely killed off the bolder males when they first began to settle these islands, and in a species were the sex ratio tends to be biased in favor of males, any trait that would have increased a female’s survival would have definite consequences in the population genetics of the species. That means that the “shy” trait could have easily become expressed in the population, simply because humans would have low tolerance for aggressive behavior.  Dragons today generally avoid people.

Finally, females of this species are capable of reproducing via parthenogenesis. Males in this species are larger, and if conditions became so bad that all the large males died off, some of the females would still be able to reproduce anyway.  Because of how the lizards’ sex chromosomes work, they can only produce male offspring when they reproduce this way, which could be a way to restore males to a population that lost them through a lack of food resources.

Komodo dragons were once quite widespread across Australia and several nearby islands, but now they exist only on the islands of Wallacea. These islands are named for Alfred Russel Wallace, a co-discoverer of evolution by natural selection. Wallace noticed that the native animals of Sunda, which is the Malayan Peninsula and the Malayan Archipelago, are fundamentally different from the native animals of the islands just to their east.  The animals of Sunda generally have an Asian origin, while those of the islands to the east are more of Australian origin. The line between these islands is called the Wallace Line.

The dragons of Wallacea are of Australian origin. Their current main prey sources are all most of Asia origin. So in the Holocene, humans broke down Mr. Wallace’s Line, and the dragons grew back into their larger form. This larger dragon was the same one that hunted the megafauna of the Australian mainland, playing second fiddle to only the larger monitor called megalania (Varanus priscus).

I have often wondered what it would have been like to have seen the mammoths that lived on Wrangel and St. Paul Islands. These mammoths were the last survivors of a species that range over much of Eurasia and North America until 10,000 years ago, but they continued to survive on St. Paul Island for 5,600 years. They died off on Wrangel Island only 4,000 years ago, and they only died out because of a weird genetic mutation similar to the rex mutation in rabbits that made it harder for them to insulate their bodies on that cold island.

But by several accidents of their biology, the Komodo dragons have not undergone the same fate. They still exist as a relict population.

We have a hard time living with large predatory animals. They tend to inconvenience our way of life pretty badly. However, the people of these islands do benefit from the dragons. They attract a lot of tourists and their dollars. There is real economic benefit to having such creatures roaming about.

But I don’t know how long this can last.  Because the dragons have these shy behaviors where they avoid humans, increased tourism on these islands could greatly stress them, making it harder for them to thrive and breed. These concerns came at about the same time of a mass arrest of an animals smuggling ring that had 40 dragons in its possession, which has led the Indonesian government to ban tourists from coming to Komodo Island in 2020.

If the islanders cannot make money from tourists, though, it is very likely they will try to make some money selling the dragons to smugglers, and if authorities are not on top of things, the Komodo dragon might not survive the Anthropocene.

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lirung monitor

Well, we have a new species of monitor lizard: Varanus lirungensis.

This species was just discovered near the village of Lirung on the island of Salibabu, which is part of the Talaud archipelago, which are between Sualwesi and Mindanao, which is part of the Philippines.

German researchers discovered this new monitor species, and after analyzing its DNA and morphology, published their findings in the Australian Journal of Zoology.

This finding is important because “it highlights the high, but poorly known diversity of monitor lizards in Indonesia. Several species of water monitor have been found on Sulawesi and surrounding islands in recent years.”

Just think of the new monitor species that have yet to be discovered in Indonesia!

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