Date of Final Oral Examination (Defense)
Type of Culminating Activity
Master of Science in Biology
Jennifer S. Forbey, Ph.D.
Marie-Anne de Graaff, Ph.D.
Lisa A. Shipley, Ph.D.
Animals must balance many risks and rewards when using resources and selecting habitats. Understanding how animals make these choices requires elucidating the functional significance and interactions among habitat features. The criteria an animal uses to determine the functional quality of a resource may differ from those traditionally measured in surveys of habitat quality. Similarly, the relative value of a particular resource may vary with an animal’s physiology or behavior, or the unique combination of the resource’s characteristics. Previous studies have identified a number of specific individual, measurable, habitat parameters that influence habitat selection of a sagebrush specialist, the pygmy rabbit (Brachylagus idahoensis). We used a combination of those parameters to test the hypothesis that pygmy rabbits evaluate habitats differently based on their intended use of those habitats. We measured seven potentially toxic plant secondary metabolites (PSMs) and crude protein levels in sagebrush at and around pygmy rabbit burrows, in addition to the proximity of each plant to the burrow entrance and the concealment from aerial predators offered by each plant. We also quantified two distinct types of habitat use by pygmy rabbits by counting foraging bite marks and fecal pellets. We used model selection to determine which combinations of habitat parameters best predicted each type of use. In general, parameters representing food quality (e.g., PSMs and protein) best predicted foraging (bite marks) and parameters representing safety (e.g., concealment and distance to refuge) best predicted resting and digestion (fecal pellets). These results suggest that pygmy rabbits use different criteria when evaluating habitats for different potential uses. We also used captive feeding trials to evaluate the preference of pygmy rabbits and mountain cottontails (Sylvilagus nuttallii) for five single PSMs in sagebrush compared to a mixture of those same five PSMs. Pygmy rabbits generally showed little preference among single PSMs compared to mixed PSMs, whereas mountain cottontails—dietary generalists—exhibited strong preferences. These results suggest that specialists are better adapted to cope with both high concentrations of single PSMs and mixtures in the foods they regularly encounter than are generalists. We propose that preference for particular PSMs by an herbivore reflect faster detoxification capacity for that specific PSM. The particular parameters used by pygmy rabbits to evaluate their habitats and food resources are important to understand if sagebrush habitats are to be effectively assessed, conserved, managed, and restored. Furthermore, identifying preference for particular components of resources by animals and correlating them with diverse measurements of use may facilitate more nuanced descriptions of habitat selection across taxa.
Nobler, Jordan D., "Risky Business: Tradeoffs Between Nutrition, Toxicity, and Predation by a Specialist Mammalian Herbivore" (2016). Boise State University Theses and Dissertations. 1088.