Biogeographic, Functional, and Phylogenetic Consequences of the Pliocene to Modern in the Western Atlantic

Restricted (Penn State Only)
Christie, Max Lawrence
Graduate Program:
Doctor of Philosophy
Document Type:
Date of Defense:
June 08, 2017
Committee Members:
  • Mark E Patzkowsky, Dissertation Advisor
  • Mark E Patzkowsky, Committee Chair
  • Peter Daniel Wilf, Committee Member
  • Timothy Bralower, Committee Member
  • Todd C Lajeunesse, Outside Member
  • Pliocene
  • Pleistocene
  • Mollusk
  • Coastal Plain
  • Plio-Pleistocene Extinction
  • Phylogenetics
  • Functional Ecology
  • Biogeography
There is no historical analog for the concentrations of CO2 in Earth’s atmosphere – to find one, we must turn to the geologic record. The mid-Pliocene (~3 Ma) is the last interval when pCO2 matched today’s value of 400 ppm. As our climate moves back to a more Pliocene-like state, studying the Pliocene allows us to forecast potential changes in Earth systems. We use Pliocene to modern mollusks to understand how climate change affected ecosystems in three ways: the biogeography of species and genera, the taxonomic and functional patterns of the extinction, and the evolutionary consequences of extinction and range restriction. Using these, we hope to predict large scale patterns of biotic change as climate warms. We compiled a dataset of fossil and modern species and genera from the literature to reconstruct biogeography from the Pliocene to modern. We found that a prominent feature of modern biogeography, the biogeographic boundary near Cape Hatteras, North Carolina, was established in the Pleistocene in response to the deflection of the Gulf Stream Current near Cape Hatteras. This caused a sharp temperature break, leading to the exclusion of southern-affiliated taxa north of Cape Hatteras. We also collected a new dataset of mollusks from Plio-Pleistocene sites north of Cape Hatteras to assess the taxonomic and functional patterns of extinction. We found that while species turnover is large across the Plio-Pleistocene, functional communities remain similar across the extinction. This contrasts with the Plio-Pleistocene transition in the Caribbean, where major functional changes occurred. This is likely because habitats north of Cape Hatteras did not change greatly after the Pliocene, suggesting that large functional changes would occur if there was a shift in habitats. Lastly, we used molecular and morphological data to create a phylogeny of extinct and extant members of the bivalve family Luciniade. Our results showed that more lucinid phylogenetic diversity was lost in communities north of Florida, which is important because high values of phylogenetic diversity are associated with ecosystem stability. We also showed that the lucinids were range restricted after the Pliocene, and would be expected to expand north when climate warms.