( acks only non-host plants such as C. o...)Ants, not evil spirits, create devil's gardens in the Amazon rainforest, study finds

Chemical analysis revealed that the only compound produced by the ants' poison glands is formic acid, a toxin that is common in many ant species and, in fact, got its name from formica, which is Latin for ant. "Treatment of leaves with formic acid induced leaf necrosis on all the plants we tested," the authors write. "To our knowledge this is the first record of an ant using formic acid as a herbicide--although it is known to have bactericidal and fungicidal properties."

The ants employ a very effective system of lethal injection, notes Gordon, associate professor of biological sciences at Stanford. "The system harnesses two fundamental tools:formic acid, which many ant species use for other purposes, and the basic circulatory system of all vascular plants," she says.

A census of the rainforest from 2002 to 2004 revealed that devil's gardens grew by 0.7 percent per year. "Using this growth rate, we estimate that the largest devil's garden in our plot, with 351 plants, is 807 years old," the authors conclude. They estimate that a typical garden is tended by a single ant colony with as many as 3 million workers and 15,000 queens, adding that the presence of multiple queens "undoubtedly contributes to colony longevity."

Niche construction

"The cultivation of devil's gardens by ants is an excellent example of niche construction," Frederickson says. "By killing plants of other species, the ant promotes the growth and establishment of D. hirsuta, thereby gaining more nest sites."

The plants also benefit by increasing their biomass and eliminating the competition, says co-author Michael J. Greene, a former Sanford postdoctoral fellow, now assistant professor of biology at the University of Colorado-Denver. "This work is a truly remarkabl
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Source:Stanford University