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Chaos Among Cannibals

Scientists know that chaos is a key force behind weather patterns and stock markets. But when it comes to explaining animal behavior, chaos has been relegated to science fiction--for instance, predicting how dinosaurs go bonkers in the movie Jurassic Park. Now, however, chaos theory has gained a toehold in the natural sciences. In a report in tomorrow's Science,* scientists report the first example of a chaotic pattern in ecology: population growth in cannibalistic beetles.

Biologists Robert Costantino of the University of Rhode Island, Kingston, and Bob Desharnais of California State University, Los Angeles, knew that the flour beetle Tribolium was a good candidate for exhibiting chaotic behavior, a phenomenon hard to measure in the natural world because the data are so noisy. The beetle population is inherently unstable because adults devour their young, resulting in wild fluctuations in numbers from generation to generation.

The biologists teamed up with mathematician Jim Cushing of the University of Arizona and statistician Brian Dennis of the University of Idaho to create a computer model of the population dynamics. The model relied on published statistics on beetle behavior, such as birth and death rates. Their simulations suggested that a beetle population should become less stable as more adults died, which would allow more larvae to survive and breed. The relative numbers of larvae, pupae, and adults would fluctuate, the model predicted, in a chaotic fashion--that is, the system was so sensitive that it would be impossible to predict the size of a population based on initial conditions.

The team tested the computer predictions by putting a population of 4-millimeter-long beetles and their larvae in 24 milk bottles filled with flour and yeast. They found that if they killed almost all of the adults and allowed fewer pupae to survive in one milk bottle, the population size would vary erratically over the 80-week study. Meanwhile, populations left to their own devices remained stable.

Other experts applaud the work. "This brings a deep and theoretical idea into the realm of experimental biology," says ecologist Peter Kareiva of the University of Washington. The findings bear on natural resource management: If other species prove to be inherently unstable, it could complicate efforts to manage populations. "In pest control situations, you would have a problem," says Costantino. Killing a few beetles in your flour jar could give you more than you bargained for.

* Science Online subscribers can link to the full text of the Report.