Daniel Lauer, QBioS Thesis Defense

In partial fulfillment of the requirements for the degree of

Doctor of Philosophy in Quantitative Biosciences
in the School of Biological Sciences

Daniel A. Lauer

Will defend his dissertation:
Responses of African Mammals and Ecosystems to Environmental Change Across Space and Time

30 June 2023
9:30 AM
EBB 4029
https://gatech.zoom.us/j/91958154979

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

Annalise Paaby, Ph.D.
School of Biological Sciences
Georgia Institute of Technology

Xiuwei Zhang, Ph.D.
School of Computational Science and Engineering
Georgia Institute of Technology

Michelle Lawing, Ph.D.
Department of Ecology and Conservation Biology
Texas A&M University

ABSTRACT:
Africa is home to some of the most biodiverse mammalian assemblages on Earth, but their diversity is threatened by human activities and rapid climate change. If we are to conserve Africa’s mammals, we must understand how they and their surrounding ecosystems respond to changing environmental conditions across space and time. I explored these responses in this dissertation, as I investigated the mechanisms through which species, communities, and ecosystems persist or become imperiled in the face of environmental change. In Chapter 1, I examined how past biodiversity losses in herbivorous megafauna may have impacted the fundamental relationships between megafaunal functional traits and environmental conditions. I adapted traditional methods in the field of ecometrics to evaluate if trait-environment relationships were disrupted over the past 7.5 Ma (million years). I found that while biodiversity losses have occurred since 5 Ma, only those after 2 Ma coincided with such a disruption. Before 2 Ma, biodiversity losses resulted from megafaunal adaptations to expanding grasslands. After 2 Ma, conversely, losses occurred as landscapes became arid and mismatches arose between megafaunal traits and environmental conditions. Consequently, past environmental change-induced biodiversity losses may have varied in their impacts on megafauna. For Chapter 2, I moved forward to modern times and disentangled the theory that heterogeneous environments constrain species’ geographic range sizes. Specifically, I compared the influences of habitat heterogeneity (variation in habitat types across space) versus topographic heterogeneity (variation in physical elevations) on mammalian ranges. Using statistical models, I found that only the former constrains species ranges, while the latter has no influence whatsoever. Such a distinction adds nuance to prior ecological theory, and it suggests that we must conserve range-limited mammals in regions of high habitat heterogeneity. I remained in modern times for Chapter 3 but shifted my focus to the ecosystems in which mammals live. I investigated the under-explored idea that ecosystems exhibit a tradeoff between their ability to withstand disturbance events (resistance) and their capacity to recover from them (stability). Statistical models revealed that such a tradeoff exists across African protected areas, as the characteristics of more resistant ecosystems oppose those of more stable ecosystems. This tradeoff may therefore be a widespread phenomenon, and consequently, a balance between the two must be struck if ecosystems are to endure future disturbances. Finally, I looked to the future in Chapter 4, as I combined insights from the fields of ecometrics and landscape connectivity to inform future mammalian conservation efforts. Using ecometrics, I determined that trait-environment relationships will weaken in >90% of herbivorous megafaunal communities across Africa. Such communities may require changes in their species compositions if they are to maintain their ability to function. I therefore built landscape connectivity models to assess where landscapes may facilitate or impede future movements of species between communities. Based on model outcomes, I provided recommendations for where conservation efforts should protect species either in situ or by facilitating their movements. Overall, my dissertation introduces new perspectives and re-evaluates conventional wisdom to advance our understanding of mammalian responses to changing environments.