How a Central-Place Forager (Callospermophilus lateralis) Modifies its Movement Behavior to Navigate a Risky Landscape and Maximize Fitness
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Authors
Hefty, Kira
Issue Date
2016
Type
Thesis
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Keywords
behavioral trade-off , optimal foraging , resource selection , spatiotemporal , time local convex hull
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Abstract
All animals need to optimize their foraging efforts to survive. Maximizing fitness, however, is more complicated than simply maximizing the net energy gained from foraging. While individuals move throughout their home ranges, they must also adopt strategies to reduce competition and predation. These conflicting behaviors can affect differential selection of food patches and how much time individuals may spend foraging in safe versus risky patch types. Golden-mantled ground squirrels (Callospermophilus lateralis) are granivorous rodents that are widespread throughout mountainous regions of western North America. C. lateralis primarily depends on the ephemeral availability of seeds to survive the summer and winter torpor. Unlike their scatter-hoarding and pilfering competitors, C. lateralis larder-hoards seeds year-round in a central burrow. C. lateralis cannot always be at the burrow to defend the larder from pilferers, however, because they must leave to participate in other activities such as foraging. Additionally, when away from the burrow, individuals incur the cost of vigilance to avoid predation. Therefore, individuals must balance conflicting behaviors of larder defense, foraging activity, and antipredator vigilance to maximize fitness. I used resource selection functions and time local convex hull metrics to analyze the spatial and spatiotemporal characteristics of movement behavior for 10 C. lateralis individuals in 2014. I used 5 gram GPS loggers which recorded locations on a narrow time interval. Results suggested that seed availability, distribution of available seeds, and current energetic requirements were large factors in predicting where and how individuals traveled throughout their home ranges. Following winter torpor, energetic requirements were highest. The first seeds available existed in distinct clumps, not necessarily close to the burrow. Individuals traveled farther to access those profitable patches and selected matrices that were associated with high predation risk, but low energetic cost of travel. Individuals also spent more time in those high quality patches and less time vigilant at the burrow. When no seeds were available, individuals avoided risky matrices and stayed close to the burrow. Right before winter torpor, seeds were more randomly dispersed and individual movement patterns suggested that individuals gathered seeds closer to the burrow. Individuals may be more likely to stay closer to the burrow at this time of year to defend the larder from pilferers. Spatial analyses provided key insights as to which patches may be important to individuals seasonally, while spatiotemporal analyses indicated how much time and how frequently individuals visited these patches. Both analyses were important for understanding how individuals may be using behavioral trade-offs to maximize fitness in a dynamic and stressful environment. These same questions and analyses can be applied to many animals in many different ecosystems, and could be particularly important when making management decisions regarding species of conservation concern.
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In Copyright(All Rights Reserved)