Graduate Studies

 

First Advisor

Kate Lyons

Department

Biological Sciences

Date of this Version

Spring 2024

Document Type

Dissertation

Comments

Copyright 2024, Alexandria Brandis Shupinski. Used by permission

Abstract

Understanding how community structure is affected by various ecological, climatic, and environmental changes is a long-standing goal in ecology. However, disentangling human impacts from these other variables is difficult when using short modern timescales and anthropogenically altered communities. The fossil record provides a means to investigate community structure dynamics across critical intervals, excluding humans as a variable. Here, in three studies, I assess changes in North American mammal paleocommunity structure across the last 66 million years (Ma) at multiple temporal and spatial scales. In Chapter 1, I identify changes in mammal functional diversity (FD) locally and continentally, using three independent metrics: functional richness, functional evenness, and functional divergence. I find that the metrics were disassociated within and across spatial scales throughout the Cenozoic, except for the Paleocene when they were changing synchronously. This suggests unique dynamics in community structure, likely due to early Cenozoic mammal radiation. In Chapter 2, I quantify spatial variation in Cenozoic mammal paleocommunities using taxonomic beta diversity and functional beta diversity. I use 5-million-year time slices to assess changes in spatial distributions of taxa and traits and the relationship between taxonomic and functional beta diversity. I find that taxonomic and functional beta diversity are highly correlated, and peak during grassland expansion, likely a result of increased habitat heterogeneity. In my third chapter, I investigate the co-occurrence structure of western North American mammal across the Plio-Pleistocene transition (3-2.5 ma) during the Great Biotic Interchange. By combining co-occurrence analysis with functional diversity, I calculate how the influence of functional roles on patterns of genus associations changed across the transition. Although the functional distance between significantly associated genus pairs decreased and new mammals formed the associations, there was no significant shift in the overall co-occurrence structure. My dissertation deepens our understanding of how ecological, climatic, and environmental events impact the community structure of mammals, providing a baseline for ecological dynamics without anthropogenic influences.

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