Weak non-linear influences of biotic and abiotic factors on invasive macrophyte occurrence

Aquatic plants (macrophytes) are important components of freshwater ecosystems and serve numerous functions, both physical and biological, that help to structure aquatic communities. However, invasive macrophytes may negatively alter ecosystem properties. Non-native invasive species have been identified as a major cause of biodiversity loss and the increasing prevalence of invasive species has prompted studies to help understand their impacts and to conserve biodiversity. Studying mechanisms of invasion also gives ecological insight into how communities are structured and assembled. This study examined a set of potential factors influencing invasion including biotic resistance, exposure, and water depth using mixed-effects models on macrophyte survey data collected from twenty-nine lakes across the United States. The results of this study indicated that biotic resistance measured from native species richness, exposure due to fetch, and water depth interact, often in non-linear ways to influence probability of invasive species occurrence at a given location; however, models explained a relatively low percentage of variation in probabilities. It is likely that strong predictive principles governing macrophyte invasions do not exist, at least among comparisons across a range of ecosystem types and environmental conditions. However, ecologists should continue to search for general patterns within definable ecosystem units to increase understanding about factors contributing to invasibility.