Darwin himself didn't quite state it this way, but it must have crossed his mind that "when the cat's away, the mice will play." Now, biologists at the University of California, Davis, and Washington University in St. Louis have completed a unique study of lizard populations on tiny islands in the Bahamas that shows what happens when a natural catastrophe devastates both the cats and the mice.
On islands devoid of cats, the mice rebound more quickly. Thomas W. Schoener, Ph.D., and David A. Spiller, of the University of California, Davis, and Jonathan B. Losos, Ph.D., professor of biology at Washington University in St. Louis were studying the effects of a large predator lizard species, the curly-tailed lizard, on both its prey, a smaller species called the brown anole, and on the entire food chain on 12 baseball-diamond sized islands in the northern Bahamas. Hurricane Floyd struck the area in the fall of 1999, drastically changing the experiment.
In 1997, just months after introducing the large predatory lizard, Leiocephalus carinatus, to islands on which the smaller lizard, Anolis sagrei, lived, the biologists had been stunned to find that anole populations were just half those on six other islands where the curly-tailed lizard did not exist; this difference presumably was a result of the much larger species eating the smaller one. In late 1999, two months after the hurricane, the researchers found that anole populations on the six islands with the predator were much more greatly reduced from pre-hurricane levels than were no-predator control islands.
One year later, the control populations had all returned to their pre-hurricane numbers, but most of the populations on the predator-present islands had failed to recover and several were extinct.
"The study shows dramatically that the presence of a top predator on an island affects the vulnerability of a prey population to a catastrophic event," says Losos. "The study is rare because it
Contact: Susan Killenberg McGinn
Washington University in St. Louis