Species-Abundance Models: An Ecological Approach to Inferring Paleoenvironment and Resolving Paleoecological Change in the Waldron Shale (Silurian)

Abstract

The Silurian Waldron Shale preserves a diverse marine fossil assemblage dominated by epibenthic suspension feeders. Three paleocommunities, distinguished 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 taxonomic richness and evenness. Species-abundance data for non-strophomenid brachiopods most closely fit a log-normal distribution. The Inter-reef Community occurs below storm-wave base, contains fewer species, and is less even in abundance distribution. Rankabundance data for the non-strophomenid brachiopod fauna most closely fit a log-series distribution. The Deeper Platform Community exists below storm-wave base, and may have experienced lower oxygen concentrations. The community has low species richness and abundance, 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, biotic interactions, and disturbance may have played important roles in determining biodiversity. General environmental conditions predicted by speciesabundance models are congruent with paleoenvironmental conclusions drawn from sedimentological and paleontological data, suggesting that some paleoenvironmental and paleoecological conditions can be inferred from the ecology of a fossil indicator taxon. Many of the factors controlling diversity in biological communities may have remained the same over much of Phanerozoic time, possibly making analysis of the link between the Recent and the Paleozoic a viable foundation for predictive models for some aspects of community dynamics.