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Date of Award

12-2024

Document Type

Restricted Thesis: Campus only access

Degree Name

Master of Science in Biology

Department

Biology

First Reader/Committee Chair

Putman, Breanna

Abstract

Competition is a vital interaction that nearly all animals experience. Animals compete for resources within the environment, but these interactions may change as the environment changes. Urbanization is currently one of the most drastic environmental changes affecting resources animals may compete for. Urbanization also may change the composition of competitors, as urban areas have lower biodiversity, but invasive species are commonly introduced into urban areas. Here, we aimed to find if and how urbanization affects competition in animals by quantifying the physiological and behavioral responses of Western Fence Lizards (Sceloporus occidentalis) to competitors. As part of this research, we also aimed to understand whether urbanization affects animal responses to non-native heterospecific competitors, which are common urban residents. We studied Western Fence Lizards from two replicate urban and natural sites located in two different areas of Southern California: San Bernardino and Claremont. We verified that the population densities of lizards at urban sites were higher than those at natural sites, implying that the frequency and/or intensity of competitive interactions may differ between urban and non-urban populations. To quantify behavioral and physiological responses to competitors, we ran trials pairing Western Fence Lizards with either another Western Fence Lizard (conspecific), a non-native Italian Wall Lizard (heterospecific), or no other lizard (control). After each trial, we collected a blood sample from the focal lizard, and then ran assays quantifying their physiological stress responses, measured as plasma corticosterone concentrations. We also filmed the trials to analyze behaviors. Lastly, we considered how urbanization may affect traits related to competitive ability, such as body size, condition, and ectoparasite presence. Overall, urbanization did not impact how fence lizards respond to competitors. Instead, we found that lizards, regardless of where they came from, were the most stressed and performed the most competitive displays when paired with a conspecific competitor. Interestingly, we found that lizards basked less during heterospecific trials, which suggests the fence lizards have a displacement response towards the non-native Italian Wall Lizards and that exploitation competition would occur between these species. Lastly, urban lizards exhibited more information seeking behaviors (head scans and tongue flicks) and had a lower probability of ectoparasite infections than their natural counterparts. Overall, our study offers insight on how animals may respond to different types of competition in urban and non-urban settings. Our study also allows us to gain a deeper understanding of the displacement reactions native species have towards non-native species, demonstrating how invasive species can cause exploitation competition to displace natives from vital resources. Lastly, this study provides a direction of research that is needed to fully understand what magnitudes of urbanization may affect species interactions, and what species may be more susceptible to the effects of urbanization.

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