Density-dependent habitat selection and consequences for fitness in a fluctuating ground squirrel population
A habitat map of our study site at the Rocky Mountain Biological Laboratory in Gothic, Colorado. Squirrels have access to five microhabitat types: Aspen forest, Dry Meadow, Spruce Forest, Wet meadow, and Willow community.
Mean resource selection ratios for golden-mantled ground squirrels at two spatial scales: where an individual chooses to place its home range, or the area needed for day-to-day activities (Second Order), and where within its home range it spends most of its time (Third Order). Everything above the dotted red line indicates positive selection.
Habitat comprises a combination of resources (such as food, water, space) and conditions (for example, temperature, absence of enemies) that are critical to an animal's performance, or 'fitness' (the ability to survive or reproduce). However, selection for certain habitat types or features may vary with changing population density. While wildlife management requires understanding these habitat-fitness relationships, access to these data is rare in wild mammal populations.
I explore habitat selection decisions, including the effect of population density on selection and the fitness consequences of non-random resource use, in a population of golden-mantled ground squirrels (Callospermophilus lateralis). My research takes place at the Rocky Mountain Biological Laboratory in Gothic, Colorado, where I trap, mark, and observe individuals over 3-month periods of time as part of a long-term study.
After assessing habitat use on two different spatial scales, results show that golden-mantled ground squirrels preferentially select for dry meadow habitat, and they select against other habitat types, such as wet meadow (Veratrum plant communities) and willow communities. A series of statistical models suggest that squirrels that share space with fewer neighbors, or that have access to a greater number of perches, such as rocks or other vantage points from which squirrels could look out for predators, were more likely to survive from one year to the next. This work furthers our understanding about the causes and consequences of changes in habitat use, providing insight to wildlife management and conservation.
Predictive models show that access to perches, from which golden-mantled ground squirrels can gain predator visibility, influences habitat selection. As the number of perches within a given space increases, preferred use of that space increases.
Golden-mantled ground squirrels hibernate over winter and, because our study site is at high elevation (2900 m), the summer active season is very short. Squirrels only have about 4 months to emerge from hibernation, find a mate, care for young, and then gain enough weight to have sufficient fat stores to be hibernation-ready again by the end of the season. Drawings courtesy of Elsa Cousins.