Aim The likelihood of a species successfully passing through all stages of the human-mediated invasion process and becoming established at new locations is often determined by phenotypic characteristics. Among species, phenotypic similarity is negatively correlated with phylogenetic distance, but examples of independent evolution of traits in unrelated taxa do exist. Using marine bryozoans as model organisms we predict that, given the selectivity of the invasion process, the phylogenetic relatedness among established non-indigenous species in a region is either higher or lower than that among the native assemblage, but not the same.
Location Sixteen port and marina environments around New Zealand (the principal sites of establishment of most non-indigenous bryozoans), and coastal habitats of the entire New Zealand coastline.
Methods We use average taxonomic distinctness (avTD) as a measure of phylogenetic relatedness and taxonomic ‘breadth’ of species assemblages. We compare values of avTD between native and non-indigenous bryozoan assemblages at two spatial scales and examine whether assemblages in port environments represent phylogenetically restricted and morphologically distinct subsets of the regional coastal bryofauna.
Results At a nationwide and a local scale, the phylogenetic relatedness among non-indigenous bryozoans was no different from that among members of the native assemblage. However, native bryozoans inhabiting port and marina environments had a significantly reduced taxonomic breadth and higher phylogenetic relatedness than the pool of ‘available’ native bryozoans from surrounding coastal habitats. Non-indigenous species were on average six times more prevalent than native species in ports. There were no differences in morphological characteristics between native and non-indigenous bryozoans from ports and natural environments.
Main conclusion We found no evidence that a successful passage through the stages of the invasion process results in a taxonomically distinct non-indigenous assemblage. However, patterns of relatedness among native and among non-indigenous species may be influenced by the nature of the study environment.