MINNEAPOLIS / ST. PAUL--Invasions by exotic species have bedeviled ecosystems from lawns and farms to prairies and oceans. Recent invaders of North America include zebra mussels, purple loosestrife and Eurasian watermilfoil. In 1958 British ecologist Charles Elton hypothesized that communities with diverse arrays of organisms were better equipped to resist invaders. Now, a study at the University of Minnesota has confirmed the connection between biodiversity and resistance to ecological invasion in a prairie ecosystem. The work suggests that plant communities, whether intact areas of native prairie or plots of land undergoing restoration, will suffer less from exotic species invasions if a diverse mix of species is present. The work will be published in the June 6 issue of Nature.

Elton, who has been called the father of ecology, published a 1958 book on invasions of exotic species in which he proposed his idea, which is known as the Diversity-Resistance Hypothesis. Since then, many scientists have explored the hypothesis, said Theodore Kennedy, a graduate student in ecology and lead author of the Nature paper.

"Researchers studying sedentary marine invertebrates have found that diverse communities make more complete use of the limited space available to them, and this leaves invaders with no place to settle," he said. "But the mechanism by which diverse plant communities keep out newcomers was previously unknown."

Kennedy and his colleagues asked whether land supporting relatively large numbers of prairie plant species would do a better job of excluding plants of Eurasian origin. They studied 147 square plots of land, each three meters on a side, at the university's Cedar Creek Natural History Area near the Twin Cities. Each plot had been planted with either 1, 2, 4, 6, 8, 12 or 24 grassland plant species, and the researchers had already noticed more weedy biomass in the less diverse plots. For two years they ceased weeding and examined rel
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Contact: Deane Morrison
morri029@umn.edu
612-624-2346
University of Minnesota
5-Jun-2002

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