In partial fulfillment of the requirements for the degree of

Doctor of Philosophy in Biology

In the

School of Biological Sciences

Julia A. Schap

Will defend her dissertation

 Integrating Paleobiological Insights to Evaluate Climate Impacts on Small Mammal Communities

22 April 2024

10:00 AM

EBB 4029

https://gatech.zoom.us/j/8018417051

Thesis Advisor:

Jenny McGuire, Ph.D.

School of Biological Sciences

Georgia Institute of Technology

Committee Members:

Lin Jiang, Ph.D.

School of Biological Sciences

Georgia Institute of Technology

William Ratcliff, Ph.D.

School of Biological Sciences

Georgia Institute of Technology

Benjamin Freeman, Ph.D.

School of Biological Sciences

Georgia Institute of Technology

Jessica L. Blois, Ph.D.

School of Natural Sciences

University of California, Merced

Biodiversity is greatly threatened by human-induced landscape changes, with species being forced to quickly adapt to new climates or attempt to track preferable climates along a fragmented landscape. New strategies integrate paleobiological perspectives and conservation biology better inform biodiversity conservation within these changing ecosystems. Small mammals, here rodents and lagomorphs, are a vulnerable group to environmental and habitat changes due to their small home ranges and limited dispersal ability. However, more work needs to be done exploring the shifts in abundance, and resulting functional diversity, of small mammals in response to past climate changes. In this dissertation, I examine the effects of changing climate, particularly precipitation, on small mammal community composition and ecological function. In Chapter 1 I focused on a single fossil site, Natural Trap Cave (NTC), and described multiple diversity metrics including relative abundance, richness, and evenness of microvertebrate taxa from approximately 23 ka to 2.5 ka. I found that most changes in the community were driven by changes in abundance rather than extirpations. I then compared the small mammal data to previously studied sites of similar age to place NTC in an environmental context. After establishing the small mammal community composition at NTC, in Chapter 2 I focused on using the functional traits of the small mammal taxa as a proxy for paleoenvironmental interpretations across the same three time periods as Chapter 1. I focused on tooth crown height as a proxy for precipitation, locomotor pattern as a proxy for openness, diet as a proxy for macrovegetation diversity, and body mass as a proxy for temperature. I then compared the functional trait trends to pollen and carbon isotope proxies from the cave. I found that functional traits were able to help align the timing of previous proxies and provide nuance about environmental conditions. In Chapter 3 I expand my study region and test the competition and coexistence hypotheses in small mammal communities across 11 North American fossil sites since the Late Pleistocene. I used linear models to analyze the correlations of taxon-dependent and taxon-free diversity metrics against environmental variables across three spatial scales: continental, biome, and individual taxon. I found mixed support for each hypothesis depending on the scale of analysis. I found support for the competition hypothesis at the continental scale and support for the coexistence hypothesis at the biome scale. At the individual taxon scale, taxa were grouped into wet-adapted or dry-adapted, and I found significant differences in their responses to changes in the precipitation of the driest month. For Chapter 4, I turn my focus to the small mammals of Africa to examine the trait-environment relationship between tooth crown height, hypsodonty, and annual precipitation. I first built a maximum likelihood model using modern correlations between community-averaged hypsodonty and annual precipitation for 10, 374 communities across Africa. After finding strong correlations in the modern, I generated trait-based estimates of paleoprecipitation for 26 well-sampled fossil localities over the last 5.7 Ma in eastern Africa. I compared precipitation trends temporally and spatially across Ethiopia, Kenya, and Tanzania and found spatial heterogeneity through time.