PS 11-95 - Effects of resource availability and variability on seasonal space use and resource selection of feral ungulate populations

Background/Question/Methods

Space use and resource selection derive from habitat conditions and animals’ requirements, which both change over time and lead animals to adjust their habitat selection patterns accordingly. Because energy expenditure associated with searching for resources is lower in more productive and homogenous environments, animals have the smallest ranges in such conditions. Using a small and consistent range should result in constant habitat selection patterns when resource heterogeneity (i.e., variability in space and time) is low, and availability is high. In contrast, in seasonal and heterogenous environments, we expect to detect variable patterns of space use and habitat selection across time. We tested the effects of habitat availability and heterogeneity on seasonal space use and resource selection of two feral burro (Equus asinus) populations in the United States: one in a subtropical Sonoran Desert ecosystem of Arizona and the other in a temperate high desert pinyon-juniper ecosystem of Utah. The two ecosystems have different topographic features, annual precipitation, availability of surface water, vegetation communities, and level of human activity. We used GPS locations of female burros (n = 50 in the Sonoran Desert, n = 24 in pinyon-juniper high desert) to delineate seasonal home ranges and evaluate seasonal resource selection patterns.

Results/Conclusions

We found Sonoran Desert burros had smaller home ranges and constant patterns of seasonal resource selection across a year, likely due to the presence of a freshwater lake in the area which made water a non-limiting resource. In the temperate pinyon-juniper ecosystem, we found larger seasonal home range sizes and more fluctuating patterns of resource selection compared to the Sonoran Desert population, due to less water availability, seasonal variation in resource availability, and lower predictability of resources from year to year. Human presence was the most important factor affecting home range size of burros in the Sonoran Desert ecosystem in which burros selected for areas near human recreation. Feral burros are descendants of domestic donkeys and as such can acclimate to humans. In contrast, spatiotemporal variation in vegetation biomass and distance to surface water significantly affected home range size of burros in the temperate high desert ecosystem, which had almost no human recreation activity. Multiple factors influence feral burro resource selection in the two ecosystems we investigated. We note that the donkey ancestor, African wild ass (Equus africanus) in their native environments are dependent on surface water, which strongly influences their distribution and behavior, like feral burros in our study.