Community invasibility: from pattern to process across multiple spatial scales in an old-field ecosystem

Biological invasions threaten biodiversity, and understanding the factors that influence a community’s susceptibility to invasion informs both management of invasive species and conservation of biodiversity. The biotic resistance hypothesis postulates that communities with greater number of competitors, predators and/or pathogens will resist biological invasions. The underlying mechanism of biotic resistance, in the realm of competition, is that in species-rich communities harbor fewer open niches for introduced species to colonize therefore decreasing the probability of invasion. My dissertation research evaluated the role of native species diversity, as well as other biotic, abiotic and landscape factors shaping exotic species richness at multiple spatial scales in an old-field ecosystem. I found that old-field communities with greater native diversity are more invasible, having greater exotic richness, at multiple spatial scales. Additionally, I investigated the role of native species diversity, biotic and abiotic factors shaping patterns of abundance by an invasive species, Lespedeza cuneata, at multiple spatial scales. Lespedeza is a rank one invasive species in several U.S. states including Tennessee due to its potential ecological impacts. I found Lespedeza abundance to be negatively associated with the abundance of dominant species, as well as with the abundance of other N-fixing species (mostly native to North America). I then conducted two field experiments which addressed the role of dominant taxa identity, in particular, the genera Solidago and Verbesina affecting old-field community structure and invasibility by Lespedeza (i.e. establishment). The second experiment investigated the role of resource availability structuring an old-field community and early establishment by Lespedeza. Overall, my findings suggest that native species diversity, abiotic and landscape factors influence multiple spatial scales.