Collaborative Research: Burrows as buffers: do microhabitat selection and behavior mediate desert tortoise resilience to climate change?

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Climate extremes increasingly exceed physiological thresholds for organisms, constraining species distributions and ultimately leading to habitat loss. Resilience to these changes depends on interactions between environmental features, behavior, and physiology that enable species to access suitable microclimates. Ecosystem engineers are species that modify their environment by creating structures, such as burrows, which can provide more stable temperature and humidity, buffering occupants against temperature extremes. The actions of these organisms are important not only for their own persistence but to enable other species to access suitable microclimates. The Mojave desert tortoise is an ecosystem engineer that creates burrows for shelter and nesting and is threatened with extinction, in part due to climate change. The youngest tortoise life stages - eggs, hatchlings, and juveniles - are particularly vulnerable to temperature extremes due to their small size and limited ability to modify their environment. These life stages rely on maternal nest placement or small mammal burrows for protection. This project aims to understand how desert tortoises modify their environment through burrow creation, to characterize how thermoregulation is achieved via burrow use, and to measure the effectiveness of burrows to buffer against rising temperature across life stages, with a particular emphasis on nesting females and early life stages. This research will provide new data on the resiliency of each life stage to climate extremes and will inform life stage-specific models of species distribution under future climate scenarios, identifying sites that may become climate refugia. This work will develop grade-specific educational modules and classroom kits that integrate active desert tortoise conservation research and will implement these modules in local classrooms. This project will also provide training opportunities for K-12 teachers, undergraduate students, a graduate student, and a post-doctoral trainee. This project is being supported via a joint program involving the Divisions of Environmental Biology and Integrative Organismal Systems and the Paul G. Allen Family Foundation.This research takes a mechanistic approach to evaluate the role of behavioral and physiological flexibility in determining resilience to climate change for the endangered Mojave desert tortoise across life stages, an important ecosystem engineer. The research seeks to characterize temperature sensitivity of eggs and maternal nesting behavior; test the effects of temperature and hydric status on juvenile burrow use, burrow morphology, and body temperature; quantify the thermal buffering capacity of behavior and burrows across age classes in wild tortoises; and use respirometry to characterize temperature effects on energy expenditure, water loss and thermal preference. These studies will provide key physiological parameters for life stage-specific mechanistic niche models (MNMs) of response to altered climate to identify optimal habitat for desert tortoises that will persist into the future. Finally, this research will test MNM predictions by collecting environmental data from model-selected sites. By identifying climate refugia and core conservation areas, these models will inform future focal sites for Mojave desert tortoise recovery activities, including restoration and assisted migration. More broadly, results will be relevant for the extended group of burrowing species and commensal organisms that use burrows, and lead to improved empirical and modelling methods for forecasting the impacts of climate change on this diverse group of organisms.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.