EXAMINING PREDICTORS OF INVASION SUCCESS USING A MOLECULAR PHYLOGENY AND THE LATE CENOZOIC FOSSIL RECORD OF BIVALVIA

Darwin's naturalization hypothesis predicts that potential colonizers are less likely to become successfully established if they are more closely related to native taxa, as negative interactions such as competition strengthen with increasing ecological similarity. Alternatively, the presence of closely related native taxa may indicate favorable conditions for potential colonizers that would promote successful establishment. Here, we integrate the rich fossil record of late Cenozoic bivalves along the western coast of North America with a dataset of functional traits and a molecular phylogeny to assess the impact of relatedness and ecological similarity on how biodiversity is established and maintained in novel environments. We examine patterns of colonization from the open ocean, through restricted connections, into the embayment formerly present in the San Joaquin Basin of central California from 27 Ma to 2.5 Ma. By comparing the relatedness of successful colonizers to the native fauna in the basin with the relatedness expected through random assembly, we find that colonization success in the San Joaquin Basin is not strongly linked with unusually close or unusually distant relatedness, suggesting that competition plays a minor role in community assembly at the geographic and temporal scale of our study. Our results highlight the complexity of factors affecting the success of invasion events and demonstrate the potential benefits of integrating phylogenies and fossil data to better understand long-term ecological dynamics.