Giant rodents are often attributed to works of science fiction, but according to a new study, there is more truth to it than mere figments of a writer's imagination.
Researchers at Duke University have discovered that animals, such as mice, rats and gerbils, are 17 times more likely to grow to gigantic proportions when left to survive on an island than anywhere else.
In a study published in the journal Proceedings of the Royal Society B, biologists Louise Roth and Paul Durst examined data collected from over 1,000 populations of rodents representing more than 60 different species from around the world.
The dataset used for the research included hamsters, squirrels, porcupines, mice and rats. The rodents ranged in size from a small 0.2-ounce harvest mouse to a large 50-pound North American beaver.
While there was nothing odd about the size of the capybara, a rodent native to South America that could grow up to 100 pounds, the researchers wanted to find out how other species of rodents could reach sizes beyond the average for their kind over time.
Roth and Durst wanted to know where the largest hamsters or the smallest squirrels in the world live, and the answer was islands.
In the 182 islands the researchers investigated, more than half of the populations of rodents they saw belonged either to the top or bottom 2.5 percent for size for their respective species.
One example is the Coues' rice rat (Oryzomys couesi), which the researchers think arrived at the island of Cozumel from Guatemala and Mexico. Populations of the rodent on the island have grown more than twice as large as their counterparts living in the mainland.
Durst added that the deer mice found on the Gulf Islands off the Vancouver coast are twice the size of those living in the mainland of North America.
The smallest rodents Roth and Durst discovered lived on islands that are dry and hot. Instead of the lush green flora of most islands, these ones were either brown or barren.
The Asian Finlayson's squirrel, for one, has significantly decreased in size after migrating to the island of Ko Lan in Thailand.
Durst said this is because the animals do not have enough resources that they need in order to grow big.
The varying sizes of animals on islands have been a popular topic for scientists.
In 1964, evolutionary biologist J. Bristol Foster studied the trends in sizes for animals living on islands and in the mainland. He observed that large animals that migrate to islands become smaller, while small animals often become larger. Foster's theory was later dubbed as the "island rule."
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