Huge Hamsters and Pint-Sized Porcupines Thrive On Islands: Researchers Test 'Island Rule' of Rodent Evolution

ScienceDaily (Mar. 23, 2012) — From miniature elephants to monster mice, and even Hobbit-sized humans, size changes in island animals are well-known to science. Biologists have long believed that large animals evolving on islands tend to get smaller, while small animals tend to get bigger, a generalization they call "the island rule."

A new study by researchers at Duke University and the National Evolutionary Synthesis Center in Durham, N.C. puts that old idea to the test in island and mainland rodents.

"Some of the size changes observed in island animals are pretty dramatic," said Paul Durst, a doctoral student at Duke and the lead author of a study appearing in the April issue of The American Naturalist. The fossil remains of dwarf elephants found on the Mediterranean island of Cyprus, for example, suggest that they shrunk by more than 90 percent over evolutionary time. Island giants are impressive too -- an extinct group of West Indian rodents known as giant hutias are estimated to have weighed up to 440 pounds, or as much as an American black bear.

But some animals still prove a puzzle. "Large animals like elephants and deer have a pretty consistent pattern. They all tend to get small. But it's more complicated for other animals such as rodents," Durst said.

http://www.sciencedaily.com/releases/2012/03/120323134934.htm