Flexible resource use strategies of a central-place forager experiencing dynamic risk and opportunity

Abstract

Background: Movement decisions made in space and time define how wildlife meet competing extrinsic and intrinsic demands to maximize fitness. Differential selection of resource patches provides one example of how to measure how animals balance conflicting demands. We hypothesized that individual spatial selection of patch types between dynamic seasons would signify flexible strategies used to minimize risk and optimize foraging efforts.

Methods: We used data collected from GPS loggers on golden-mantled ground squirrels (Callospermophilus lateralis) to model selection or avoidance of resources in two seasons of seed availability and one season in which no seeds were available. Movement decisions were measured in short-term discrete time intervals using high resolution location data. Selection or avoidance of specific resource features that entail fitness consequences were then assessed using resource selection functions.

Results: Seasonality of food availability, food type, and spatial distribution of food largely influenced how individuals selected resources within their home ranges. Overall, when seeds were available, individuals mediated risks of predation and loss of food by using patches closer to refuge and selected intermediate distances to the burrow. When food was not available, individuals minimized exposure to heightened risk by staying close to the burrow and avoiding riskier patch types.

Conclusions: Results indicate that individuals used flexible, dynamic strategies to select habitat patches which may allow them to balance conflicting seasonal demands. Advances in GPS technology for research of small mammals provide greater insight into how prey species in high risk environments differentially use resources to minimize risk and maintain fitness.

Keywords: GPS; High-resolution; Movement behavior; Resource selection; Small mammal; Trade-offs.

Fig. 1

Model generated beta estimates with 85% confidence intervals from an analysis of resource selection by Callospermophilus lateralis relative to three seasons of food availability: bitterbrush, interval (no seeds available), and pine. Selection for parameters along the y-axis are represented by positive values along the x-axis whereas avoidance of parameters along the y-axis are represented by negative values along the x-axis. Study was conducted July 15–September 30, 2014, in the Whittell Forest and Wildlife Area, NV, USA

Fig. 2

Density plots of GPS logged points from Callospermophilus lateralis depicting distance traveled from the burrow (m) during three seasons of food availability: a) Bitterbrush, b) Interval (no seed available), and c) Pine. The dark gray indicates used points (gained from GPS loggers) and the light gray indicates randomly generated available points. Study was conducted July 15–September 30, 2014, in the Whittell Forest and Wildlife Area, NV, USA

Fig. 3

Density plots of GPS logged points from Callospermophilus lateralis depicting distance traveled from the refuge (m) during two seasons of food availability: a) Bitterbrush and b) Interval (no seed available), and c) Pine. The dark gray indicates used points (gained from GPS loggers) and the light gray indicates randomly generated available points. Study was conducted July 15–September 30, 2014, in the Whittell Forest and Wildlife Area, NV, USA