Investigation of Darwin’s naturalization hypothesis in invaded macrophyte communities

Although native macrophytes are beneficial in aquatic ecosystems, invasive macrophytes can cause significant ecological and economic harm. Numerous studies have attributed invasiveness to species’ characteristics, whereas others attribute invasion to biotic and abiotic characteristics of the invaded community. It has been suggested that studying the link between invader and invaded community is key to understanding invasiveness, and that invasions can be understood through the framework of community ecology theory. Charles Darwin hypothesized that introduced species would be less likely to naturalize in areas containing closely related species [Darwin’s naturalization hypothesis (DNH)], suggesting competition between closely related species could limit naturalization potential (phylogenetic repulsion). The goal of this research was to test DNH using two species of highly invasive aquatic plants, Myriophyllum spicatum L. and Potamogeton crispus L., and assess whether results were consistent at small and large scales. Twenty-nine lakes containing invasive macrophytes were surveyed between 1997 and 2011. Invasive P. crispus occurred in 15 lakes and M. spicatum occurred in 19 lakes. There were 15 native Potamogeton species and 4 Myriophyllum . We used generalized linear mixed models with congeneric species richness data to estimate probability of invasive P. crispus or M. spicatum occupying a given sampling location. Contrary to predictions of DNH, the relationship between congeneric richness and presence of P. crispus at point and lake scales was positive. Unlike models for P. crispus , native Myriophyllum genera richness was not a significant model parameter. These results do not support DNH (the expectation of a negative relationship); furthermore, models had relatively low determination coefficients indicating very little explained variation. Although this study found no evidence for DNH, there is still a need to investigate how community assembly processes influence species invasions.