MINNEAPOLIS / ST. PAUL--An exotic species or weed trying to establish itself in a new ecosystem will have a harder time if it encounters a diverse mix of resident species rather than just a few species, according to research at the University of Minnesota. Working with prairie plants, the research team found that a rich assemblage of species repels invaders because it is more likely to contain plants occupying a niche similar to what the invader needs, as well as plants that make good all-around competitors. The findings have implications for land managers, suggesting that maintaining the native diversity of species can help keep out weeds and exotic species. The study is published in the current Proceedings of the National Academy of Sciences.

"Our study suggests that invading species that resemble resident species are less likely to get established," said Joseph Fargione, a graduate student in the university's department of ecology, evolution and behavior and first author of the study. "This makes it difficult to predict which exotic species will become problem weeds by studying the weeds alone. Their success actually depends to a large extent on the characteristics of the species already present in the ecosystem."

The researchers worked with nine-square-meter plots of land at the university's Cedar Creek Natural History Area in southern Minnesota. The plots contained between one and 24 species of prairie plants that had become well established, with 20-24 replicates at each level of diversity. The researchers introduced a mix of seeds from 27 other plants, all native to the area, to each plot. All the plants fell into one of four types, or "guilds": warm-season grasses, cool-season grasses, legumes and forbs.

In general, as the species richness of established plants increased. introduced plants from any guild did more poorly. Using statistics to tease out the repellant effects of individual plant guilds, the researchers found that each gu
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Contact: Deane Morrison
morri029@umn.edu
612-624-2346
University of Minnesota
2-Jul-2003

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