Date of Award

2024-08-01

Degree Name

Doctor of Philosophy

Department

Ecology and Evolutionary Biology

Advisor(s)

Jerry D. Johnson

Second Advisor

Brett M. Seymoure

Abstract

To thrive in an environment, individuals need to be able to forage efficiently and acquire mates. These resources are limited, and their acquisition depends upon the energy and time an individual chooses to allocate to each activity and the environmental conditions, leading to behavioral trade-offs. Different species, or even different individuals within the same population, respond to these trade-offs by employing contrasting strategies, leading to differential life-history outcomes. The overarching goal of this dissertation is to gain a better understanding of the trade-offs cryptic ambush mesopredators are facing using the western diamond-backed rattlesnake (Crotalus atrox) as a model species. Each chapter of this dissertation focuses on different aspects of these trade-offs: personality, predator-prey interactions, and camouflage strategies.In Chapter 1, I investigated personality in wild western diamond-backed rattlesnakes (Crotalus atrox) across five axes: activity, exploration, boldness, sociability, and reactivity. The objectives of this chapter were to develop a protocol to successfully test personality traits in rattlesnakes following these axes and to determine whether Crotalus atrox exhibits repeatable personality traits and behavioral syndromes. To do so, 22 wild rattlesnakes were captured and submitted to a series of captive behavioral trials. Crotalus atrox exhibited individual differences that were repeatable through time across the five previously mentioned axes. Activity was the only axis that was sex-dependent, with males moving more than females on average. Moreover, these axes were grouped into three personality dimensions: reactivity, exploration, and activity-boldness-sociability. This last personality dimension provides evidence for the presence of a behavioral syndrome (i.e., correlation between several personality axes) within this species. This chapter provides a repeatable and ecologically relevant protocol to study personality in rattlesnakes. Crotalus atrox exhibits individual behavioral differences consistent through time and behavioral syndromes comparable to other species. This chapter provides a baseline to answer questions pertinent to personality in rattlesnakes such as conflict management and will help provide insights into the secretive life of serpents. In Chapter 2, I investigated the effect of personality on the spatial ecology of the western diamond-backed rattlesnake (Crotalus atrox) and tested the predictions that bolder, more active and exploratory individuals will move more and have larger territories compared to shyer and less active individuals. I tracked 14 rattlesnakes for one year and then I assessed their personality in captivity across four different axes: activity, boldness, exploration, and reactivity. Bolder and more active individuals traveled more than shy, less active individuals, but only during the non-mating season. Shy individuals increased their movement rate significantly more than bold individuals during the mating season, thus leading to no significant difference in movements between shy and bold individuals during the mating season. Moreover, less bold and less active individuals were more responsive to the change in reproductive status. These results suggest the existence of two different strategies for resources acquisition within the same population, indicating that the pace-of life-syndrome hypothesis (i.e., species or individuals exhibit distinct set of physiological and behavioral traits that evolved with their specific life-history requirements) may be context-dependent. Ultimately, my results show that the existence of different life-history strategies within the same population are dependent upon the reproductive status of these individuals. In Chapter 3, I researched how the landscape of fear affects the foraging decisions of Crotalus atrox by investigating factors influencing detection risk and prey availability. To do so, 30 biologically accurate 3D-printed snake replicas, each associated with a game camera, were deployed at Indio Mountains Research Station for two years to estimate the spatiotemporal factors affecting prey availability and predation risk. Concurrently, 25 Crotalus atrox were radiotracked at the same site to gather activity and microhabitat selection data regarding this species. Random-forest algorithms were trained using data obtained from the game camera and applied to predict the probability of predation and the probability of prey encounter for each radiotracking event. Time of the day, month, vegetation structure, and concealment percentage all had a significant effect on the probabilities of predation and prey encounters. Overall, rattlesnakes chose to be active when and where the probability of prey encounters was significantly higher than the probability of detection by predators, thus following optimal foraging theory. In conclusion, this study showed that the combination of 3D-printed models, game cameras, and telemetry provided effective and non-invasive methods to study predator-prey dynamics. In Chapter 4, I investigated the trade-offs between background matching and thermoregulation in western diamond-backed rattlesnakes (Crotalus atrox). Rattlesnakes were predicted to better match selected microhabitats in terms of color, luminance, and pattern than random microhabitats within their home range. Body temperature was predicted to influence their body coloration with higher temperatures favoring lighter colors. Pictures of 14 radiotracked western diamond-backed rattlesnakes were taken in situ with a full spectrum camera (UV/VIS) and body temperature was recovered from internal temperature-datalogging radiotransmitters. Crotalus atrox matched the color, luminance, and pattern of the background better than a randomly selected background, thus enhancing background matching. Additionally, rattlesnake coloration varied independently of temperature indicating that rattlesnakes are behaviorally modifying crypsis regardless of thermoregulation.

Language

en

Provenance

Received from ProQuest

File Size

122 p.

File Format

application/pdf

Rights Holder

Oceane Da Cunha

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