Investigating ecological questions at the scale of individual organisms is necessary to understand and predict the biological consequences of environmental conditions. For small organisms this can be challenging because we need tools with the appropriate accuracy and resolution to record and quantify their ecological interactions. Unfortunately, many of our existing tools are only appropriate for medium to large organisms or those that are wide ranging, inhibiting our ability to investigate the ecology of small organisms at fine scales. In Chapter 1, I tested a novel workflow for recording animal movements at very fine spatial and temporal scales. The workflow combined direct observation and the mapping of locations onto high-resolution uncrewed aerial vehicle (UAV) imagery loaded on hand-held digital devices. Observers identified landscape features they recognized in the imagery and estimated positions relative to those features. I found this approach was approximately twice as accurate as consumer-grade GPS devices with a mean and median error of 0.75 m and 0.30 m, respectively. I also found that performance varied across landscape features, with accuracy highest in areas that had more visual landmarks for observers to use as reference points. In addition to sub-meter accuracy, this method was cost-effective and practical, requiring no bulky equipment and allowing observers to easily record locations away from their own location. While this workflow could be used to record locations in a variety of situations, it will be most cost-effective when also using high-resolution environmental data from a UAV. In Chapter 2, I used the workflow described in Chapter 1 to investigate blunt-nosed leopard lizard (Gambelia sila) thermoregulation at fine-scales. Recent research has suggested that the spatial distribution of temperatures is important to consider for ectotherm thermoregulation, but this work has been limited to simple artificial environments. My goal was to investigate this idea in a complex natural system for the first time. I tracked lizard movement and body temperatures at a desert site from May to July 2021. I used machine learning to combine high-resolution environmental data from a UAV with microclimate temperature data to create a model of the spatial distribution of environmental temperatures over time. I found that including information about the spatial distribution of temperatures improved the models of lizard thermoregulatory accuracy and movement rate. Because these response variables are important aspects of ectotherm energetics, this suggests that the spatial distribution of temperatures may be an important, but often overlooked, component of habitat quality. Going forward, identifying better methods to quantify the spatial distribution of temperatures would provide insights into the specific responses of ectotherms to different spatial distributions. In this work I used recent technological advances in UAVs to investigate ecological questions at the scale of a small organism. The methods developed here provide insights into the importance of the spatial distribution of temperatures for a small ectotherm. Further efforts to develop, test and utilize tools for fine-scale ecological research will advance our ability to understand species’ interactions with current conditions and predict their responses to future changes.

Recognizing how climate change will impact populations can aid in making decisions about approaches for conservation of endangered species. The Blunt-nosed Leopard Lizard (Gambelia sila) is a federally endangered species that, despite protection, remains in extremely arid, hot areas and may be at risk of extirpation due to climate change. We collected data on the field-active body temperatures, preferred body temperatures, and upper thermal tolerance of G. sila. We then described available thermal habitat using biophysical models, which allowed us to (1) describe patterns in lizard body temperatures, microhabitat temperatures, and lizard microhabitat use, (2) quantify the lizards’ thermoregulatory accuracy, (3) calculate the number of hours they are currently thermally restricted in microhabitat use, (4) project how the number of restricted hours will change in the future as ambient temperatures rise, and (5) assess the importance of Giant Kangaroo Rat burrows and shade-providing shrubs in the current and projected future thermal ecology of G. sila. Lizards maintained fairly consistent daytime body temperatures over the course of the active season, and use of burrows and shrubs increased as the season progressed and ambient temperatures rose. During the hottest part of the year, lizards shuttled among kangaroo rat burrows, shrubs, and open habitat to maintain body temperatures below their upper thermal tolerance, but occasionally, higher than their preferred body temperature range. Lizards are restricted from staying in the open habitat for 75% of daylight hours and are forced to seek refuge under shrubs or burrows to avoid surpassing their upper thermal threshold. After applying climatic projections of 1 and 2˚C increases to 2018 ambient temperatures, G. sila will lose additional hours of activity time that could compound stressors faced by this population, potentially leading to extirpation. Finally, temperature-based activity estimation (TBAE) is an automated method for predicting surface activity and microhabitat use based on the temperature of an organism and its habitat. In an attempt to lessen impacts on sensitive species and costs, we assessed continuously logged field active body temperatures as a tool to predict the surface activity and microhabitat use of an endangered lizard (Blunt-nosed Leopard Lizard, Gambelia sila). We found that TBAE accurately predicts whether a lizard is above or below ground 75.7% of the time when calculated using air temperature, and 60.5% of the time when calculated using biophysical models. While surface activity was correctly predicted about 93% of the time using either method, accuracy in predicting below ground (burrow) occupancy was 62% for air temperature and 51% for biophysical models. Using biophysical model data, TBAE accurately predicts microhabitat use in 79% of observations in which lizards are in the sun, 47% in the shade, and 51% in burrows. Heliotherms bask in the sun, and thus body temperatures can shift rapidly when the animal moves to a new microhabitat. This sensitivity, makes TBAE a promising means of remotely monitoring animal activity, particularly for specific variables like emergence time and surface activity.

Chapter 1: Animals can respond to extreme climate by behaviorally avoiding it, or by physiologically coping with it. We understand behavioral thermoregulation and physiological thermal tolerances, but water balance has largely been neglected. Climate change includes both global warming and changes in precipitation regimes, so improving our understanding of organismal water balance is increasingly urgent. We assessed the hydric physiology of endangered Blunt-nosed Leopard Lizards (Gambelia sila) by measuring cutaneous evaporative water loss (CEWL), plasma osmolality, body mass, and body condition throughout their active season. On average, G. sila had low CEWL that is likely desert-adaptive, and high plasma osmolality that is indicative of dehydration. Given that our study was in a drought year, it is reasonable to believe that every lizard measured was dehydrated to a degree. We hypothesized that throughout the G. sila active season, as their habitat got hotter and drier, G. sila would become increasingly dehydrated and watertight. Instead, CEWL and plasma osmolality showed minimal change for females and nonlinear change for males, which we hypothesize is connected to sex-specific reproductive behaviors and changes in food availability. We also measured thermoregulation and microhabitat use, expecting that more hydrated lizards would have higher body temperature, better thermoregulatory accuracy, and spend more time aboveground. However, we found no effect of CEWL, plasma osmolality, body mass, or body condition on these thermal and behavioral metrics. We posit either that G. sila tolerate dehydration to maintain activity during their brief active season, or that because every lizard was dehydrated due to the drought, they all experienced equally constrained thermoregulation and microhabitat use. Finally, G. sila spend considerable time underground in burrows, and we believe burrows serve as essential hydric, not only thermal, refugia. Our findings suggest that these lizards might benefit from artificial humid refugia and supplemental hydration, especially during drought. Chapter 2: Testing acclimation plasticity informs our understanding of functional biodiversity and applies to conservation management amidst our rapidly changing climate. While there is a wealth of research on the plasticity of thermal and hydric physiology in response to temperature acclimation, there is a comparative gap for research on acclimation to different hydric regimes, as well as the interaction between water and temperature. We sought to fill this gap by acclimating Western Fence Lizards (Sceloporus occidentalis) to experimental climate conditions (crossed design of Hot or Cool, Dry or Humid) for eight days, and measuring cutaneous evaporative water loss (CEWL), plasma osmolality, hematocrit, and body condition before and after acclimation under common conditions. CEWL changed plastically in response to the different climates, with lizards acclimated to Hot Humid conditions experiencing the greatest increase in CEWL. Change in CEWL among individuals was negatively related to treatment vapor pressure deficit. Plasma osmolality, hematocrit, and body condition all showed greater changes in response to temperature than to humidity or vapor pressure deficit. CEWL and plasma osmolality were positively related across treatment groups before acclimation and within treatment groups after acclimation, but the two variables showed different responses to acclimation, suggesting that they are interrelated but governed by different mechanisms. This study is among just a small number of studies that assess more than one metric of hydric physiology and that test the interactive effects of temperature and humidity. Such measurements will be essential for predictive models of activity and survival for animals under climate change.