Ecological mechanisms of invasion success in aquatic macrophytes

Aquatic plants (macrophytes) are important components of freshwater ecosystems and serve numerous purposes that structure aquatic communities. Although macrophytes represent an essential component of stable aquatic communities, invasive macrophytes 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 give insight into how communities are structured and assembled. This paper examined mechanisms that contribute to macrophyte invasion through a literature review. Mechanisms identified with this review included competition, enemy release, evolution of increased competitive ability, mutualisms, invasional meltdown, novel weapons, allelopathy, phenotypic plasticity, naturalization of related species, empty niche, fluctuating resources, opportunity windows, and propagule pressure; and were then placed within the context of the invasion process. Results of this review indicated that many invasion mechanisms have been tested with fully aquatic macrophytes with varied levels of support (i.e., some mechanisms are not supported by evidence in the context of macrophyte invasions). Future research should continue the search for evidence of invasion mechanisms that allow introduced species to establish. It is likely that general principles governing these invasions do not exist, at least among comparisons across ecosystem types. However, ecologists should continue to search for general patterns within definable ecosystem units to increase understanding about factors contributing to invasibility.