THE ECOLOGY OF TAXONOMIC TURNOVER: CHANGES IN THE LOCAL ABUNDANCE AND SPATIAL DISTRIBUTION OF TAXA THROUGH TIME

Understanding how the spatial distribution and abundance of individual taxa change as a result of regional or global environmental perturbations can provide important insights into how ecosystems are structured and how they change through time. One approach is to plot for each taxon its mean within-collection abundance against the percent of collections in which it occurs. Within-collection abundance primarily reflects the Peak Abundance (PA) of taxa. For intervals with little taxonomic turnover, percent-of-collections primarily reflects Environmental Tolerance (ET) of taxa. For intervals with high taxonomic turnover, percent-of--collections will also reflect the stratigraphic range in the regional ecosystem. Thus, this simple plot portrays information on both local abundance and the spatial and temporal distribution of taxa and permits the identification of rare taxa that occur in small numbers locally and in only a few collections, taxa that are locally abundant but restricted in occurrence to a few collections, taxa that occur in many collections but are rare to intermediate in their local abundance, and locally dominant taxa that occur in many collections. Plotting these parameters through time can 1) indicate how the local abundance and spatial distribution of individual taxa change through time, and 2) indicate what the ecological characteristics are of taxa that go extinct or invade a region as a result of an environmental perturbation. Here, we examine the ecology of a biotic invasion in the Late Ordovician of the eastern United States. We find that invading taxa fill a wide range of ecological space with respect to their local abundances and spatial distributions. Most notably, several invading taxa are locally abundant, yet occur in few collections and fill in an area of ecological space not occupied in the previous time interval.