Taxonomic and phylogenetic composition show biotic resistance to exotic invasion in acid seep springs

Abstract

Background: Few studies have incorporated the evolutionary insights provided by analysis of phylogenetic structure along with community composition to assess the effects of exotic invasion on freshwater wetlands. Here, we assess the taxonomic and phylogenetic relationships among acid seep springs to investigate the potential homogenization or resistance of communities due to invasion of an exotic grass. Results: Multivariate community analyses indicated differences in community and phylogenetic composition and dispersion among acid seep springs, associated with gradients in soil moisture, canopy cover, and phylogenetic diversity. By contrast, univariate analyses showed differences in taxonomic diversity but not phylogenetic diversity among acid seep springs. Conclusions: Despite exotic invasion, individual acid seep springs remained taxonomically and phylogenetically distinct from each other. Taxonomic and phylogenetic diversity metrics revealed different aspects of composition, reinforcing the importance of including both in analyses of plant communities for understanding community assembly following exotic invasion and for management purposes. Within acid seep springs, taxonomic and phylogenetic composition appear to be driven more through environmental filtering by light and moisture than by the competitive effects following invasion of an exotic grass in support of Elton’s biotic resistance hypothesis.