MODES OF PHANEROZOIC MARINE PALEOCOMMUNITY TURNOVER: A MODEL-SELECTION APPROACH

A long-running debate in paleoecology focuses on the relative importance of neutral versus niche-based processes in driving ecological turnover on geological timescales. This issue remains unresolved for a variety of reasons including methodological limitations, uncertainties about the patterns predicted by different mechanisms, and the complications of the stratigraphic record. Here we bring both new simulations and new analytic methods to bear on understanding prevalent modes of turnover in the benthic marine fossil record. We use the SedFlux stratigraphic model to simulate turnover patterns in specific facies under different community assembly scenarios, and the PaleoTS R package to evaluate relative support for different modes of change through time (unbiased random walk, directional random walk, and stasis). As expected, ecological drift simulations are generally best fit by an unbiased random walk, though there is a bias towards stasis if the number of timesteps or the sample size is low. For niche tracking simulations, within a single lithofacies, stasis is preferred over unbiased random walks, but only when niche breadths are wide. We also find that the most frequent mode of turnover shifts from stasis in the Paleozoic to random walk in the post-Paleozoic. Although this pattern is consistent with a general decrease in niche breadths through the Phanerozoic, it is confounded by differences in habitat type and in both the length and sampling density of time series. Additional work with longer and higher-resolution time series, as well as simulating interactions between ecological drift and niche-based dynamics, has the potential to shed more light on the drivers of paleoecological turnover.