Bite force: why islanders become giants among lizards

A Skyros wall lizard (Podarcis gaigeae) takes a bite of ecologist Erik Svensson’s finger. Credit, Erik Svensson.

Species evolve quickly on islands. These “natural laboratories” often offer freedom from predators and competitors, isolation, and new foods and resources. Animals on islands tend to be larger or smaller than their mainland relatives. First described by Foster in 1963, this pattern is so striking that it was dubbed “the island rule” by Leigh van Valen ten years later. Many subsequent studies have investigated, debated, and refined Foster’s rule and related

A Skyros wall lizard (Podarcis gaigeae) demonstrates the strength of its bite. Credit, Erik Svensson.

hypotheses explaining the evolution in body size when animals are isolated on islands. In the August 2015 issue of Ecology, Anna Runemark, Kostas Sagonas, and Erik Svensson report that diet has contributed to the development of gigantism of the Skyros wall lizard (Podarcis gaigeae) on islets around the Greek island Skyros. On the main island, Skyros lizards typically eat ants, wasps, and bees. On islets where on harder-to-chew fare like beetles and isopods were more common, and the lizards frequently dined on them, the lizards were larger, with wider heads and a correspondingly stronger bite.

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