Understanding the factors that contribute to extinction risk is essential for predicting the response of species to environmental change. For many extant and extinct taxa, intrinsic biological factors play a critical role, but their relative importance is poorly known. Using the Paleogene fossil record of marine mollusks from the Gulf and Atlantic Coastal Plains of the eastern United States, I present new methods for unveiling rare diversity and a series of multivariate analyses of the direct and indirect effects of intrinsic biological factors on extinction risk through the early Cenozoic. I show that combining museum, literature, and field data using a modeling approach can provide a more comprehensive estimate of taxonomic richness and abundance without substantial increase in current sampling effort. I then assess the contributions of abundance, body size, and geographic range to the duration of bivalve species and find that geographic range has the strongest direct effect on extinction risk and that an apparent direct effect of abundance is explained entirely by its covariation with geographic range. The influence of geographic range is broadly manifest, explaining variation in extinction risk in three ecologically-disparate bivalve clades. Body size also contributes significantly to extinction risk, but in opposing directions in different clades, such that it has no net effect for bivalves as a whole. Using structural equation modeling, I reveal indirect effects of both abundance and body size on extinction risk via their positive influence on geographic range size. Lastly, I evaluate the stability of intrinsic biological correlates of extinction risk over the early Cenozoic by comparing a model in which these effects were invariant over time with several time-dependent models. I find that geographic range size always had a significant positive effect on extinction resistance but its strength varied over the early Cenozoic in tandem with variation in extinction intensity and clade diversity. My dissertation provides a new understanding of the interacting forces which drive extinction in ancient communities, and offers an explicit methodological framework for assessing general versus specific controls on extinction risk over the variable history of Earth and life.
|Commitee:||Kidwell, Susan M., Lidgard, Scott, Wagner, Peter J., Wootton, J. Timothy|
|School:||The University of Chicago|
|School Location:||United States -- Illinois|
|Source:||DAI-B 70/08, Dissertation Abstracts International|
|Subjects:||Ecology, Geology, Paleontology|
|Keywords:||Extinctions, Fossils, Macroecology, Multivariate, Rarity|
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