Different ecological and historical mechanisms are thought to determine the success of nonnative species in native recipient communities (e.g., dispersal dynamics, adaptation, biotic interactions). Charles Darwin posited two alternative hypotheses to explain the success of nonnative species based on their relatedness to incumbent natives: coexistence between them should be (i) more likely with greater relatedness (due to trait similarity that correlates with better matching to the environment), or (ii) less likely (due to biotic interference). The paradox raised by the opposing predictions of these two hypotheses has been termed ‘Darwin’s naturalization conundrum’ (DNC). Here, using plant communities over a long time span and across an experimental fire gradient at Cedar Creek Ecosystem Science Reserve, we aim to evaluate the DNC by explicitly incorporating taxonomic, functional and phylogenetic information. To do so, we apply a novel approach based on ‘focal-species’ that allows describing the taxonomic, functional and phylogenetic structure of species co-occurring with a given focal species in local communities, while species presence and abundance are also taken into account.
Results/Conclusions
Among the 243 species recorded in all permanent plots at Cedar Creek Ecosystem Science Reserve, 26 species were classified as nonnative species. Among these 26 nonnative species, four were classified as highly invasive (rapidly increased in abundance), 16 as increasing (increased in abundance under certain conditions) and six as persisting (abundance relatively stable over time). Overall, we found that co-occurrence patterns of the 26 nonnative species within local communities did not follow a general tendency of phylogenetic clustering or overdispersion—in other words they were not found to occur more with closely or distantly related native species—instead, we found that co-occurrence patterns depended on species-level evolutionary history and functional traits that regulated the colonization and persistence of nonnatives within native communities.