Elton's hypothesis revisited: Can species-rich understory of the longleaf pine ecosystem resist invasion by Imperata cylindrica?

In the 1950s Charles Elton hypothesized that more diverse communities should be less susceptible to invasion by exotic species (biodiversity-invasibility hypothesis). The biodiversity-invasibility hypothesis postulates that species-rich communities are less vulnerable to invasion because vacant niches are less common and the intensity of interspecific competition is more severe. The understory of the longleaf pine ecosystem is characterized as species rich.  We tested Elton’s hypothesis using cogongrass (Imperata cylindrica), a nonindigenous grass invading large areas of the Southeastern United States.  The study was conducted at the Black Water River State forest in northwest Florida over a two year period.  Results indicated no significant relationship between the rate of cogongrass spread and native plant species richness, functional richness, and cover of the invaded community. Increased species or functional richness may increase the use of resources; however, the extensive rhizome/root network possessed by cogongrass and its ability to thrive under shade may allow for its persistence in a diverse community. Underlying reasons for why no relationship was observed may be simply due to the tremendous competitive ability of cogongrass or the narrow range of species richness, functional richness and cover observed in our study.