In a large manipulation of the environment two researchers have used entire islands in the Bahamas to test evolution. The biologists focused on the traits of running and body size of native lizard populations to test whether intra- or inter-specific competition was the greater driver of evolution.
On different islands these researchers alternatively used bird-proof netting to limit predation, introduced snakes to increase predation, or added more lizards to increase competition. They found that predation was essentially random with neither body size or overall speed making much difference to who would be eaten for lunch. On the other hand, when intra-specific competition increased having a larger body size and faster movement allowed certain lizards to access scare resources more effectively. It was this force, the researchers found, that drove the lizards evolution and not the predation.
While this is fascinating research and provides yet more evidence that evolution does actually occur (and within our lifetime) the biologists are quick to point out that this finding may not be replicating in other predator/prey relationships where predation could be more of an evolutionary factor.
Ryan Calsbeek, Robert M. Cox. Experimentally assessing the relative importance of predation and competition as agents of selection. Nature, 2010; DOI:10.1038/nature09020
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