"How diverse the ecosystem is and how a particular species interacts with the rest of the system is perhaps more important than the actual number of species," said Mathew Leibold, an associate professor in the department of ecology and evolution, and co-investigator of the study, which is published in the April 25 issue of Nature.

Most previous studies have shown a "saturating" effect, which suggests that an ecosystem can lose a major portion of species before it harms the remainder of the biota. That is, the system doesn't break down until it's too late.

"But we found that there is a much bigger effect initially," Leibold said. "When you start losing species, you start losing productivity right away."

"This is not an extremely surprising result," said lead author Amy Downing, a former U. Chicago graduate student who currently is an assistant professor of zoology at Ohio Wesleyan University. According to Downing, most previous studies focused on the effects of biodiversity in much simpler ecosystems.

In this study, the researchers used a more complex system, involving a larger portion of the food web. On average, ponds have four main "trophic" levels: plants (such as algae), herbivores (such as zooplankton), carnivores (insects or fish) and top carnivores (predators of other carnivores).

In the past, scientists have studied single trophic-level systems, mainly focusing on plant communities. Leibold and Downing used three of the four trophic levels in their study.

"We added a little bit of realism to our study," Downing said. "We don't have worlds that just consist of plants. We have worlds that have plants, those plants have
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Contact: Catherine Gianaro
cgianaro@uchospitals.edu
773-702-6241
University of Chicago Medical Center
24-Apr-2002