Island Born Lizards Are Less Prone to Fleeing Than Those Found on Mainlands

One of Charles Darwin's theories was island prey animals are relatively tame when not exposed to predators. No comparative studies had addressed this theory until now and the results confirm Darwin's notion. Biologists William E. Cooper of Indiana University-Purdue University Fort Wayne in Fort Wayne, Ind., R. Alexander Pyron of The George Washington University, and Theodore Garland Jr., of The University of California at Riverside decided to test Darwin's notion that those animals not exposed to predators are less prone to fleeing. Their findings are published in the Proceedings of the Royal Society B.

Marine iguana

Photo by Charlesjsharp/Wikipedia

The Galápagos marine iguana (Amblyrhynchus cristatus albemarlensis) was part of a previous Flight Initiation Distance study that Cooper and his colleagues examined to help confirm Charles Darwin's notion that island prey animals were more approachable than those living on mainlands.


Cooper and his colleagues tested Darwin's hypothesis, looking at previous studies of 66 island and mainland lizard species from five continents and determined that those found on islands without notable predators were tamer than those found on continents. Those studies had data on Flight Initiation Distance (FID), or the distance where a lizard flees to avoid becoming a predator's next meal. Those studies showcased the fact that a human can get closer to lizards that evolved on islands than those found on mainlands, and the further the island is from a land mass, the tamer the lizards become.

"Our study confirms Darwin's observations and numerous anecdotal reports of island tameness. Findings of several studies cited above support Darwin's proposals that escape responses are reduced on remote islands, because predators are scarce or absent there, and natural selection under reduced predation should favor prey that do not waste time and energy developing and performing needless escape," the authors state in their paper. "A similar reduction in response to predators that are absent occurs in isolated aquatic ecosystems, especially freshwater systems, where prey are highly vulnerable to introduced predators."

The full paper, "Island tameness: living on islands reduces flight initiation distance" can be found here.

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