Date of Graduation

8-2023

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Biology (PhD)

Degree Level

Graduate

Department

Biological Sciences

Advisor/Mentor

Beaupre, Steven J.

Committee Member

DuRant, Sarah E.

Second Committee Member

Willson, John D.

Third Committee Member

Gifford, Matthew E.

Keywords

Climate; Energy; Lizard; Physiology; Resource; Temperature

Abstract

Climate change poses threats to organisms regarding direct and indirect effects of warming temperatures. Laboratory studies and predictive models are useful for understanding how temperature influences organisms, and the future of species’ life history and persistence. This dissertation expands upon current approaches to thermal studies and climate models, while investigating effects of warming nighttime temperature and altered prey availability on individuals and populations. Lizards in the genus Sceloporus were used as model organisms, as they are broadly distributed with thermally sensitive physiologies. The first dissertation chapter conducted meta-analyses to examine temperature-induced changes in food consumption, activity, and life history. Prominent knowledge gaps were identified on indirect effects of warming temperatures, despite the abundance of climate change models on lizards. Mechanistic studies concerning energy budgets are important for assessing changes in fitness and life history. Rates of food consumption and digestion are the primary drivers determining the size of an individual’s energy budget. Digestive processes are often among the most sensitive traits to temperature changes for many ectotherms and are therefore important for understanding the effects of climate change and local environment on fitness. Thermal sensitivity of physiological processes can vary locally, which many climate models fail to consider. The second dissertation chapter explored variation in thermal sensitivity of digestion, identifying distinct differences among populations of Sceloporus lizards. Additionally, many studies focus on stable temperature treatments, as opposed to daily temperature cycles experienced in nature. Daily temperature cycles, and patterns of temperature experienced, provide more realistic conditions for assessing the effects of temperature, which may improve our current understanding of organismal thermal biology. The third dissertation chapter compared data from stable and cycling treatments, finding differences between methods, which varied among physiological processes. Additionally, processes differed between two daily temperature cycles consisting of different temperature patterns. Together, the first three dissertation chapters identified a need for data on combined direct and indirect effects of climate change, focused on a singular population, and under realistic projected daily temperature cycles. Therefore, the fourth dissertation chapter quantified changes in energy budgets due to warming nighttime temperature (direct effect) and prey availability (indirect effect) prairie lizards (Sceloporus consobrinus). Chapter four identified interdependent effects of warming nighttime temperature and prey on energetics, with the magnitude of change being a prominent factor dictating performance. The fifth dissertation chapter projected the energy budgets quantified in the fourth chapter, in context of reproductive output and population growth rates, among nine potential scenarios. Projections exemplified how warming nighttime temperatures interact with prey availability to reduce reproductive output, and subsequent population growth rates. The current dissertation identified the importance of using methods that replicate realistic conditions to examine mechanistic questions, while considering local variation. Studies on individual energetics and combined abiotic and biotic changes offer mechanistic data to inform population projections. Future studies should consider more taxonomic groups and temperature scenarios, as well as additional factors which may change in tandem with temperature in the future.

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