BEYOND MOLLUSKS: A MULTI-TAXIC EVALUATION OF THE FIDELITY OF BETA DIVERSITY

Beta diversity (β) is used to explore spatiotemporal components of biodiversity within and across habitats. While widely used in paleontological studies, applications of β rely on the assumption that quantitative measures of β, when applied to time-averaged and inherently biased fossil or recently accumulated death assemblages, represent a meaningful ecological metric. Recent studies suggest that, although biased, β diversity patterns may be preserved in the fossil record. However, direct fidelity tests in present-day environments are few, and limited to one higher taxonomic group: mollusks.

Here we examine the fidelity of β-turnover (change in composition from one sampling unit to another along a gradient) and β-variation (within-habitat heterogeneity in community composition) using multiple higher taxonomic groups of modern marine invertebrates from shallow continental shelf environments (Onslow Bay, North Carolina, USA). By adding taphonomic filters to live survey data, replicating common types of paleontological data, comparisons can be made between the patterns observed in (1) the live community, (2) the preservable portion of the live community, and (3) robust mollusks.

β-turnover generally increased with increasing difference in depth and onshore-offshore distance between localities, suggesting that depth-related habitat variation is a driving factor controlling marine community turnover in the sampled coastal region. The overall pattern of spatial variation is preserved in both types of restricted datasets, suggesting that the fossil record can provide meaningful estimates of β. However, β decreases as data are restricted based on preservation potential, with the lowest turnover rates observed for the robust mollusk dataset.

Lower β for preservable taxa and mollusks may result from preservation biases that restrict data to a specific subset of taxa present in the original communities. Despite such biases, fidelity between the living community and simulated death assemblages is high, consistent with previous work on live-dead comparisons of mollusks. These results support the applicability of metrics of β diversity to the fossil record and also suggest that death assemblages in present-day habitats may provide a useful baseline for conservation and resource management.