Examination of the abundance and geographic range of rare taxa: survivorship patterns of Miocene-Pliocene marine invertebrate fauna of the Virginia Coastal Plain

Abstract

The concept of rarity is vital to the understanding of extinction selectivity. Ecological studies have demonstrated that rare taxa (e.g., those with small local abundance and limited geographic range) experience significantly elevated rates of extinction. Past paleontological work supports these conclusions with respect to geographic range and extinction selectivity. However, research to date, does not suggest that the same positive correlation applies when considering abundance-based selectivity in the fossil record. Analysis of the Miocene-Pliocene marine invertebrate fauna of the Virginia Coastal Plain indicates similar variable results with respect to abundance and geographic range during a period of background extinction. An overarching pattern of no selectivity across all taxa is illustrated through both a non-parametric victim-survivor comparison utilizing multiple abundance metrics and a comparison of ? diversity partitioning to abundance-selectivity null models. Examination of solely the gastropod members of the community indicates extinction-selectivity for rare gastropods. The relationship between geographic range and selectivity is highlighted through a non-parametric victim-survivor comparison of geographic range data assembled from past work and quantified by the number of embayments in which particular taxa are found. The finding of rare-taxa selectivity among gastropods is strengthened by a comparison of abundance and geographic range, which indicates that victims tend to have low local abundance or limited geographic range. Therefore, there is an overall implication of both no selectivity and rare-taxa selectivity, suggesting spatial and taxonomic variance in ecological patterns of selectivity during background extinction