Species-abundance models: An ecological approach to inferring paleoenvironment and resolving paleoecological change in the Waldron Shale (Silurian)

The Silurian Waldron Shale preserves a diverse marine fossil assemblage dom inated by epibenthic suspension feeders. Three paleocommunities, distinguis hed from one another by taxonomic composition, relative abundance of taxa, and fossil distribution, are represented in the Waldron. The Biohermal Community exists above storm-wave base and has the greatest t axonomic richness and evenness. Species-abundance data for non-strophomenid brachiopods most closely fit a log-normal distribution. The Inter-reef Com munity occurs below storm-wave base,: contains fewer species, and is less e ven in abundance distribution. Rank-abundance data for the non-strophomenid brachiopod fauna most closely fit a log-series distribution. The Deeper Pl atform Community exists below storm-wave base, and may have experienced low er oxygen concentrations. The community has low species richness and abunda nce, and is dominated by strophomenid brachiopods. This community cannot be fitted to either the log-series or log-normal distributions, but resembles a broken stick distribution. In all three Waldron communities, water depth, habitat heterogeneity, bioti c interactions, and disturbance may have played important roles in determin ing biodiversity. General environmental conditions predicted by species-abu ndance models are congruent with paleoenvironmental conclusions drawn from sedimentological and paleontological data,, suggesting that some paleoenvir onmental and paleoecological conditions can be inferred from the ecology of a fossil indicator taxon. Many of the factors controlling diversity in bio logical communities may have remained the same over much of Phanerozoic tim e, possibly making analysis of the link between the Recent and the Paleozoi c a viable foundation for predictive models far some aspects of community d ynamics.