Spatial ecology of ground-dwelling squirrels

Golden-mantled ground squirrels (Callospermophilus lateralis)  are a small-bodied species (150-300 g) and as such are presumed to be asocial and territorial, with non-overlapping home ranges that individuals defend through aggression. However, this classification was supported by sparse data that did not take into account kin relationships among adults. Moreover, evidence of philopatry (females tend to stay where they're born) and home range overlap suggests that golden-mantled ground squirrels either are not territorial, or that territoriality is influenced by density.

I combine field observations, spatial mapping, and modeling to quantify spatial organization in this species (home range size, overlap among neighboring squirrels), as well as how that organization may change as a function of varying population density. Preliminary results show significant spatial overlap among females, with an apparently higher degree of overlap during years of greater population density. This suggests that this species may be facultatively territorial.

In addition to researching population-level trends in space-use, studying spatial patterns on the individual level can help us to better understand how behavior may scale up to influence population or even species-level trends. For example, I am calculating whether consistent individual differences in behavior, or personality, may influence individual movement patterns. I also studied litter relocation behavior, in which a female moves her offspring to a new location as a form of maternal investment. That work, which provided the first detailed description of this behavior in yellow-bellied marmots (Marmota flaviventer) and golden-mantled ground squirrels, found that costs associated with moving offspring are likely not as great as the benefits, such as decreased risk of predation or improved habitat quality.

Screen Shot 2019-09-17 at 21.53.33.png

Home ranges of individual golden-mantled ground squirrels during two high density years (purple polygons) and two low density years (orange polygons). Spatial overlap among squirrels appears to vary as a function of density, suggesting this species may be facultatively territorial.

Screen Shot 2019-09-17 at 21.36.44.png

Home ranges (95% minimum convex polygons) of adult female golden-mantled ground squirrels over the course of one active summer season at the Rocky Mountain Biological Laboratory, Colorado.

Individual-level variation in movement speed is captured through this visualization of 6 squirrels moving across the study site, where, for example, the individuals depicted by the blue and yellow tracks don’t move as far within a given period of time as do the squirrels depicted by purple and orange tracks.

Screen Shot 2019-09-18 at 14.30.41.png

 A  schematic representation of total distance moved by a female yellow-bellied marmot when relocating her litter of four from natal burrow A to new burrow B. The marmot shuttles pups individually to burrow B, before returning to burrow A to obtain each subsequent member of the litter.