Invasive species present challenges for restorations and insight into factors that make them successful could help reduce management costs and increase restoration success. One avenue of research is propagule pressure (PP) as a predictor of invasive species success. In angiosperms, PP is generally measured as the number of seeds, and sometimes the number of species entering across a season. More seeds provide more chances for individuals to grow (and analogously with the number of species) and so should increase invasive species growth, if they find favorable conditions.
Few studies have investigated whether invasive species affect one another’s establishment success through increasing competition. For species that evolved under similar selection pressure, more closely related species should have more similar niches and so compete more. We thus tested for an inverse relationship between the phylogenetic similarity of incoming invasive species and invasion success. If phylogenetics is a major factor, it could predict potential invasive success without as much research into individual biological traits.
To examine the effects of phylogenetics and PP on invasive species success, we collected invasive species biomass (as a proxy for success) and number of seeds and species across the 2017 spring and summer growing season in 48 experimental tallgrass prairie plots. Phylogenies were constructed using MatK, rbcL, and ITS1 genetic data from GenBank.
Results/Conclusions
Our results indicate that species-specific traits may have a larger effect on a species’ establishment success than the identity of or number of other invasive species. There was a significant correlation between the number of invasive species seeds and invasive species biomass. However, neither the number of invasive species in the propagules nor the phylogenetic diversity of incoming invasive species within said propagules correlated to invasive species end of season biomass. There were only minor correlations when the number of invasive species within a propagule was examined in a phylogenetic context. The data indicated that PP in the form of the number of seeds entering a plot was a major limitation to invasive species establishment. It is also possible that micro-scale environmental factors may play a role in determining species establishment success such that even species that can grow in a nearby region may not be able to establish in a given plot. Future conservation efforts that focus on reducing PP rather than the composition of a group of invasive species may have the greatest effectiveness at least in newly created restorations.