ANN ARBOR, Mich.---Ever since a forward-thinking trio of physicists identified the phenomenon known as self-organized criticality---a mechanism by which complexity arises in nature---scientists have been applying its concepts to everything from economics to avalanches.
Now, researchers at the University of Michigan and the University of Toledo have shown that clusters of ant nests on a coffee farm in Mexico also adhere to the model. Their work, which has implications for controlling coffee pests, appears in the Jan. 24 issue of the journal Nature.
The basic idea of self-organized criticality often is illustrated with a sand pile. As you trickle sand onto the cone-shaped pile, the cone grows and grows until it reaches a "state of criticality" where it stops growing. Add more sand, and the grains just slide down the sides in mini-avalanches.
"What physicists have done---both mathematically and physically---is look at how many grains of sand actually fall with each avalanche," said John Vandermeer, the Margaret Davis Collegiate Professor of Ecology and Evolutionary Biology and one of the Nature paper's authors. "What they find is that most avalanches involve one or two sand grains, and relatively few avalanches involve hundreds of sand grains." Such a pattern---with small versions of a phenomenon being more common than big ones---characterizes what's known as a power law, a sort of fingerprint of systems that exhibit self-organized criticality.
What do avalanches have to do with ants" Vandermeer and co-author Ivette Perfecto, a professor at the U-M School of Natural Resources and Environment, have been studying ants and other associated insects in a 45-hectare (111-acre) plot on an organic coffee farm in southwestern Mexico for three years and wondered whether the spatial distribution patterns they observed could be explained through the concept of criticality. With Stacy Philpott, then a U-M graduate student and now an assi
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University of Michigan