Species diversity and biological invasions: Relating local process to community pattern

In a California riparian system, the most diverse natural assemblages are t he most invaded by exotic plants. A direct in situ manipulation of local di versity and a seed addition experiment showed that these patterns emerge de spite the intrinsic negative effects of diversity on invasions. The results suggest that species loss at small scales may reduce invasion resistance. At community-wide scales, the overwhelming effects of ecological factors sp atially covarying with diversity, such as propagule supply, make the most d iverse communities most likely to be invaded.