Paleocommunity response to extinction
Layou, Karen M.
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A regional extinction occurred among marine macroinvertebrate taxa during the Late Ordovician in eastern North America. Previously unexamined changes to the diversity structure of paleocommunities across the extinction boundary were quantitatively addressed through the development of null models of changes in diversity and evenness metrics as functions of percent extinction. The model results were compared to analyses of field censused paleocommunities from shallow and deep subtidal facies within three regions of the Appalachian Basin, including the Jessamine Dome of central Kentucky, the Nashville Dome of central Tennessee, and the Valley and Ridge of western Virginia.The null models show that variations in the evenness metric, Pielou's J, and variations in the relationship between alpha diversity and the highest level of beta diversity within a sampling hierarchy, are unique to different conditions of extinction selectivity with respect to tax on abundance. Field data from the entire basin suggest this extinction targeted rare taxa, however, at some local scales, abundant taxa appear to be more affected. The field data also highlight a number of geographic and environmental variations in paleocommunity response to this extinction. Deep subtidal communities in Virginia were most significantly affected during this event. In general,across the extinction boundary, the diversity and evenness metrics decline, the taxonomic composition of paleocommunities shifts, and relative abundances of taxa within ecological guilds varies. Despite these factors, the extinction led to minimal changes in the relative abundance distribution of taxa within paleocommunities, given the small magnitude of change in diversity and evenness metrics. These quantitative analyses highlight the complexity and variability in paleoecological response to the extinction.