Patterns of biodiversity and co-occurrence of native and nonindigenous species at Great Lakes coastal margins

Studies that assess the ecological processes that allow establishment by a nonindigenous species in the Laurentian Great Lakes can help elucidate general ecological processes. The Great Lakes has such varied habitats that observations of any general patterns in ecological processes, involving both native species and nonindigenous species, likely pertain elsewhere. Studies relating biotic interactions and interaction-neutral processes to invasibility are numerous, but they have been largely inconclusive. This thesis evaluates hypotheses linking biotic interaction (i.e., richness, evenness, and dominance) and neutral-interaction (i.e., dispersal/propagule pressure) processes of several taxonomic groups (birds, diatoms, fishes, macroinvertebrates, and wetland vegetation) to invasibility at various spatial scales and sample sizes. These hypotheses were assessed using synoptic sample collections from various locations throughout the US Laurentian Great Lakes coastal margins influenced by varying types and levels of anthropogenic disturbance. I tested hypotheses relating biotic resistance versus habitat suitability to invasion by a nonindigenous amphipod. Results supported the view that biotic facilitation by dreissenid mussels and distribution of suitable habitats better explain the distribution of the nonindigenous amphipod than anthropogenic disturbance and biotic resistance. I evaluated hypotheses relating richness, evenness, and relative species dominance to invasibility and the occurrence of native and nonindigenous species using data compiled for various taxonomic groups from several hundred locations along the US coastline of the Laurentian Great Lakes. Across taxonomic groups, trends of native and nonindigenous species distributions were inconsistent with regulation by biotic interaction related processes. Regulation by neutral processes, such as propagule pressure or habitat suitability may better explain patterns. Native species distributions were correlated with habitat suitability and habitat hydrogeomorphology, and ranges reflect biogeographic history. The factors that constrain nonindigenous species are arguably a variation of those that constrain native species distributions, thus indicating that similar factors constrain both native and nonindigenous species. The general accuracy of these synoptic findings was assessed by comparing biodiversity estimation performance of data resulting from intensive sampling protocols. A method proposed by Olszewski (2004), which is alternative to rarefaction and statistical estimators for species richness, was also tested. This method uses the evenness component of biodiversity and requires a limited number of samples for estimations. My findings indicated that true biodiversity measures cannot be attained efficiently from surveys. Since such measures are unattainable, interpretation of biodiversity studies would benefit from closer examination of detectable species (i.e., common species) that likely have a stronger impact on community processes, than rare and/or transient species. Nonindigenous species that become widespread and abundant are likely governed by the same factors that regulate common native species. Ecology would benefit from linking studies of the factors that regulate the distribution and abundances of common species, both native and nonindigenous, and the dynamics between biodiversity and ecosystem properties and processes