That living on islands makes animals tamer than their mainland counterparts, a theory proposed by Charles Darwin 150 years ago, is supported in a new study.
A team of scientists found island lizards to be much more "friendly" than their mainland counterparts, allowing researchers to approach them more closely than mainland lizards allowed.
The researchers, from the University of California, Riverside; Indiana University; Purdue University, Fort Wayne and George Washington University published their findings in Proceedings of the Royal Society B.
The team calculated the flight initiation distance, the predator–prey distance when the prey starts to flee, against other factors like island area, distance to mainland and differences in prey and predator sizes. They used lizards from five continents and islands in the Atlantic and Pacific Oceans and the Caribbean and Mediterranean Seas.
Tameness in the lizards increased as distance from the mainland increased, meaning that lizards were more approachable the farther the island was from the mainland.
According to Theodore Garland, a professor of biology at UC Riverside, the escape response time reduced on islands because of fewer predators, or the total absence of them. Natural selection led these animals to not waste energy on developing and performing needless escapes.
"When prey are very small relative to predators, predators do not attack isolated individual prey," Garland said. "This results in the absence of fleeing or very short flight initiation distance."
The study seems to have validated a casual observation made by Darwin, while studying animals on the Galapagos Islands and developing his theory on natural selection.
"Our study confirms Darwin's observations and numerous anecdotal reports of island tameness," said Garland. "His insights have once again proven to be correct, and remain an important source of inspiration for present-day biologists."
[Proceedings of the Royal Society B]