Make it simpler: Alien species decrease functional diversity of coastal plant communities

Questions (a) Are there differences in abundance-weighted functional trait values between native and alien species in coastal plant communities? (b) Which functional traits are associated with a higher level of invasion in these communities? (c) Do functional diversity patterns differ between native and alien species? (d) Is alien species occurrence linked to small-scale functional homogenization effects on the resident native species? Location N-Adriatic coastal ecosystems (Marano and Grado lagoon, Friuli Venezia Giulia region, Italy). Methods We sampled coastal vegetation within two habitats (foredunes and saltmarshes) along nine belt transects in two sampling sites. Plant species richness and abundance were assessed in 128 plots along with a suite of plant functional traits. We tested for differences in community-weighted means between native and alien species within the two habitats, and Linear Mixed Models provided insights into traits fostering the invasion success among alien species. To check for potential functional homogenization driven by alien species invasion, we explored functional diversity patterns of native and alien species (beta and gamma functional diversity) and the relationship between alpha functional diversity and alien cover. Results Alien species had lower functional diversity than natives and were characterized by lower leaf construction costs coupled with lower drought resistance and higher water transport efficiency. The most abundant aliens were the ones minimizing carbon investment for leaf construction. In addition, we also found evidence for small-scale functional homogenization driven by alien invasion. Conclusions Our results suggested that native species adopt a resource conservative strategy whereas alien species are characterized by a higher resource acquisition capacity (i.e., acquisitive strategy). Our data also confirmed that alien species are less functionally diverse than natives, potentially driving the community towards small-scale functional homogenization, resulting in a loss of species and a reduction in the functional space.