Relatedness and the composition of communities over time: evaluating phylogenetic community structure in the late Cenozoic record of bivalves

Understanding the mechanisms that prevent or promote the coexistence of taxa at local scales is critical to understanding how biodiversity is maintained. Competitive exclusion and environmental filtering are two processes thought to limit which taxa become established in a community. However, determining the relative importance of the two processes is a complex task, especially when the critical initial stages of colonization cannot be directly observed. Here, we explore the use of phylogenetic community structure for identifying filtering mechanisms in a fossil community. We integrated a time-calibrated molecular phylogeny of bivalve genera with a spatial dataset of late Cenozoic bivalves from the Pacific coast of North America to characterize how the community that was present in the semi-restricted San Joaquin Basin (SJB) embayment of present-day California was phylogenetically structured. We employed phylogenetic distance-based metrics across six time bins spanning 27-2.5 Ma and...