Spatial heterogeneity of buffaloberry (Shepherdia canadensis) in relation to forest canopy patterns and its importance for grizzly bear (Ursus arctos) resource selection

  • Author / Creator
    Denny, Catherine K
  • Spatial heterogeneity inherent in the environment influences how animals respond to their surroundings, especially as it relates to the variability of their food resources. Heterogeneity in specific elements of vegetation, such as the spatial pattern of a single plant species, can be defined based on patch distribution and abundance. Patterns of plant food resources at the landscape-scale will be particularly important for wide-ranging wildlife species that perceive surrounding heterogeneity at a broad spatial extent. Canada buffaloberry (Shepherdia canadensis) is a shrub common to montane and boreal forests of western North America with its fruit being a primary seasonal resource for birds and mammals, including grizzly bears (Ursus arctos). The objectives of this study were first to relate the spatial heterogeneity of buffaloberry shrubs to forest canopy patterns, and second to examine how buffaloberry shrub heterogeneity affected grizzly bear space use (resource selection) during the fruiting season. Forest canopy and buffaloberry shrub presence were measured in the field with line-intercept sampling along ten 2-km transects, stratified to different levels of canopy cover and variability in canopy, in the Rocky Mountain foothills of west-central Alberta, Canada. Effects of canopy on buffaloberry in the understory were scale-dependent, with shrub presence negatively related to evergreen canopy cover and positively related to deciduous canopy cover. The fractal dimensions of both overstory forest canopy and understory buffaloberry shrubs were estimated using box-counting methods to evaluate spatial heterogeneity based on patch distribution and abundance. Buffaloberry patch heterogeneity was positively related to evergreen canopy heterogeneity, but was unrelated to that of deciduous canopy. This demonstrates that evergreen canopy measurements can be used to scale up buffaloberry patch distribution and abundance across the landscape at a spatial extent relevant to bears. Grizzly bear GPS radio-telemetry data for the daytime period were used to estimate resource selection function (RSF) models using predicted abundance and fruit production of buffaloberry at both the patch- and landscape-scales. Measures of surrounding shrub abundance and variability in fruit density were the most important factors explaining habitat selection during the fruiting period. In particular, variability in surrounding fruit density was strongly and positively related to selection of buffaloberry patches by grizzly bears, suggesting the presence of trade-offs between maximizing use of resource patches and the use of complementary resources or cover for day bedding. Clarifying the landscape heterogeneity of food resources and how this influences animal habitat use can provide insight into how consumer-resource interactions may be altered in the future, and can thus inform wildlife conservation and management.

  • Subjects / Keywords
  • Graduation date
    Fall 2016
  • Type of Item
  • Degree
    Master of Science
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.