Leanne Martin, a recent graduate of EEB, and Brian Wilsey recently tested how exotic grassland species altered beta diversity (diversity caused by species turnover from place to place) in 42 grassland sites along a latitudinal gradient from Minnesota to central Texas. The paper was published in the journal Ecology.
It has long been hypothesized that exotic species lower beta diversity and homogenize the flora, and Martin and Wilsey found that this indeed was the case within sites. However, beta diversity was higher across exotic-dominated grasslands than across native-dominated grasslands along the entire latitudinal gradient. This was due to high local dominance, and changing identity of dominant species across exotic sites, suggesting that interpretation of homogenization effects should consider spatial scale.