THE ROLE OF ABUNDANCE IN DETERMINING EXTINCTION RISK OF THE LATE NEOGENE GASTROPODS OF WESTERN ATLANTIC

While ecological theory predicts that abundant taxa should have an advantage over rare ones during biotic crises, there is little consensus in the paleontological literature. In the present study, we test the relationship between abundance and extinction risk among marine gastropod genera from the Late Neogene fossil record of Florida, which records a regional mass extinction that resulted in the loss of 70% of Pliocene taxa. Relative abundances of 250 gastropod genera (30,000 specimens) were measured from bulk sampling and combined with data of rare, list-only taxa from literature representing four Pliocene-Pleistocene units. Geographic range (measured as the number of marine sub-provinces occupied by a genus) is also included in our analyses as abundance covaries with geographic range. Following previous work, both non-parametric statistics and logistic regression were used to test the relation between abundance and extinction risk.

Abundant taxa had a significant advantage in survivorship over rare taxa during the late Neogene crisis, even after controlling for geographic range. Although logistic regression has been suggested as the better suited model over commonly used parametric or non-parametric statistical tests, our results suggest that choice of analysis or null hypothesis did not influence the findings. Thus, the late Neogene extinction of Western Atlantic marine gastropods, despite its severity, did not disrupt the macroevolutionary selective regime predicted by ecological theory.