The Evolution of 'Island Tameness': How Predators and Isolation Shape Species

More than 150 years ago, Charles Darwin noticed that animals on the Galapagos Islands seemed to be more docile and tame than mainland creatures. While he attributed this to the fact that there are fewer predators on remote islands, scientists are taking a closer look at island tameness.

In this latest study, the researchers focused on lizard populations on 37 Greek islands. They found that as the diversity on an island increases, so does the distance at which small lizards start to flee when they are approached. It's an anti-predator response that scientists call the flight initiation distance. In addition, the researchers found that the longer an island has been isolated from the mainland, on average, the longer the lizards would wait before fleeing from a predator.

What's interesting is that this study reveals that animals living on small, long-isolated islands are more at risk from introduced predators. This means that these types of islands should receive priority in conservation efforts.

"Being so fearless, these populations are extremely susceptible to any novel predator that's introduced," said Johannes Foufopoulos, co-author of the new study, in a news release. "In fact, island tameness has caused numerous island-species extinctions at the hands of human-introduced predators and pets. Determining what factors lead to the loss of effective anti-predator responses is critical because it provides a fundamental understanding of evolutionary processes on islands and also helps conservation managers predict which island species are at most risk."

Yet not all predators were equally important in shaping behavior. Fast-moving predators, such as mammals and hawks, were much more influential than sit-and-wait predators, such as vipers.

"In summary, our results indicate that loss of anti-predator defenses in a serious problem for island organisms and suggest that small, long-isolated island populations stand at highest risk from invasive predators and, as such, should receive priority in conservation efforts," said Kinsey Brock, first author of the new study.

The findings are published in the journal Evolution.

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