Academic journal article The Science Teacher

Survival of the Fittest

Academic journal article The Science Teacher

Survival of the Fittest

Article excerpt

By using entire islands as experimental laboratories, two Dartmouth College biologists have performed one of the largest manipulations of natural selection ever conducted in a wild animal population. Their results, published online in the journal Nature, show that competition among lizards is more important than predation by birds and snakes when it comes to survival of the fittest lizard.

"When Tennyson wrote that nature is 'red in tooth and claw,' I think the image in his head was something like a Discovery Channel version of a lion chasing down a gazelle," says Ryan Calsbeek, an assistant professor of biology at Dartmouth College and a coauthor of the study. "While that may often be the case, intense natural selection can also arise through competition. Sometimes, death by competitor can be more important than death by predator."

To show this effect, the researchers covered multiple small islands in the Bahamas with bird-proof netting to keep predatory birds at bay. Other islands were left open to bird predators, and on still other islands, the researchers added predatory snakes to expose the lizards to both bird and snake predators. Next, they tracked the lizards over the summer to record which lizards lived and which died on the different islands.

"We found repeated evidence that death by predators occurred at random with respect to traits like body size and running ability" says Robert Cox, a researcher at Dartmouth and Calsbeek's coauthor. …

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