Relationships Between Climatic Variation and Population Dynamics of the Threatened Mohave Ground Squirrel

Climate change has elevated the intensity and frequency of droughts, affecting wildlife population dynamics. In arid environments, drought can have severe consequences for life history parameters, such as survival and emigration, especially for species of conservation concern. We analyzed a 34-year dataset in a mark-recapture framework to estimate demographic parameters for Mohave ground squirrels (Xerospermophilus mohavensis), a threatened species confronted with climate change and drought. Specifically, we examined the influence of individual-, geographic-, and environmental-related variables on survival, emigration, emigration fidelity (i.e., the probability that an animal that has moved away from the study site will remain away), capture probability, recapture probability, and number of unmarked animals, the latter of which allowed us to estimate population size. We captured 1404 squirrels at four study sites. Overall, male squirrels had lower survival and higher emigration rates than did female squirrels, and juveniles had lower survival than adults. Emigration was lower at the highest-elevation study site than at other sites. Survival of male squirrels increased with higher levels of vegetation greenness. At two of the four study sites, emigration of squirrels of both sexes decreased with higher levels of vegetation greenness. No variables influenced emigration fidelity or number of unmarked animals. Initial capture probabilities were lower for males than for females, and for juveniles than for adults, whereas recapture probabilities were lower for adults than for juveniles. Population size fluctuated over time with several peaks during the study separated by periods of low numbers, which occasionally fell to zero at each site. By the end of the study, adult population size at the two sites with the longest-term monitoring was 70% lower than its peak early in the study. Demography of Mohave ground squirrels was characterized by a large amount of variation, leaving them highly vulnerable to additional stress from climate change. Our findings suggest that conservation management actions, such as prioritizing sites with consistently high levels of vegetation greenness, protecting contiguous areas of suitable habitat, and enhancing emigration success of squirrels, may promote the long-term viability of this species as climate changes. They also illustrate how long-term population monitoring can be used to support management for other conservation-relevant species affected by climate change and drought.