Journal Article

Group-size-mediated habitat selection and group fusion-fission dynamics of bison under predation risk

Beyer, Hawthorne L., Fortin, Marie-Eve, Fortin, Daniel, Duchesne, Thierry, Courant, Sabrina, Dancose, Karine

2009

Overview

For gregarious animals the cost-benefit trade-offs that drive habitat selection may vary dynamically with group size, which plays an important role in foraging and predator avoidance strategies. We examined how habitat selection by bison (Bison bison) varied as a function of group size and interpreted these patterns by testing whether habitat selection was more strongly driven by the competing demands of forage intake vs. predator avoidance behavior. We developed an analytical framework that integrated group size into resource selection functions (RSFs). These group-size-dependent RSFs were based on a matched case-control design and were estimated using conditional logistic regression (mixed and population-averaged models). Fitting RSF models to bison revealed that bison groups responded to multiple aspects of landscape heterogeneity and that selection varied seasonally and as a function of group size. For example, roads were selected in summer, but not in winter. Bison groups avoided areas of high snow water equivalent in winter. They selected areas composed of a large proportion of meadow area within a 700-m radius, and within those areas, bison selected meadows. Importantly, the strength of selection for meadows varied as a function of group size, with stronger selection being observed in larger groups. Hence the bison-habitat relationship depended in part on the dynamics of group formation and division. Group formation was most likely in meadows. In contrast, risk of group fission increased when bison moved into the forest and was higher during the time of day when movements are generally longer and more variable among individuals. We also found that stronger selection for meadows by large rather than small bison groups was caused by longer residence time in individual meadows by larger groups and that departure from meadows appears unlikely to result from a depression in food intake rate. These group-size-dependent patterns were consistent with the hypothesis that avoidance of predation risk is the strongest driver of habitat selection.

• Publisher: Ecological Society of America
• Subject: Animals / Bison / Bison - physiology / Bison bison / Bison bison bison / Buffalo / Canada / conditional logistic regression / Ecology / Ecosystem / exploitative competition / Foraging / free-ranging plains bison / GPS radio collars / group behavior / group dynamics / group effect / Group size / group size effects / habitat preferences / Habitat selection / Habitats / Heterogeneity / Meadows / Models, Biological / National parks / Perceptual localization / physiology / Population Dynamics / Predation / predation risk / predator avoidance / predator-prey relationships / Predatory Behavior / Predatory Behavior - physiology / Prince Albert National Park / Regression analysis / resource selection function / resource selection functions / Risk / Saskatchewan / seasonal variation / Seasons / Snow-water equivalent / Social Behavior / Summer / Time Factors / Vegetation / wildlife habitats / Winter / Wolves / Wolves - physiology