Effect of Early Seral Forests on Grizzly Bear (Ursus arctos) Food Supply, Habitat Selection, and Tradeoffs with Mortality Risk Associated with Roads via an Individual-based Model
Creators: Souliere, Christopher Michael
Publisher: name: University of Alberta Library
Year: 2023

<p>Large-scale disturbances can shift the distribution, abundance, and quality of animal food resources, which in turn, can influence how habitat is used by individuals. This not only increases competition among conspecifics, but can also lead to lower survival since individuals are more likely to encounter humans in human-dominated landscapes. A key challenge for wildlife managers is therefore to understand how to best minimize the effect of large-scale disturbances – which can be partly anthropogenic in origin – while simultaneously enhancing their positive effect. In this thesis, I explored the effects of large-scale disturbances and distribution of food resources on grizzly bear (Ursus arctos) habitat supply, including the tradeoff between individual health, via body condition, and survival, via mortality risk as it relates to road density, in a human-modified landscape. First, I tested whether harvested areas can act as surrogates to wildfires with respect to grizzly bear food supply by comparing and quantifying key fruit-bearing and herbaceous grizzly bear foods among post-harvest and post-fire disturbance types and at relatively early stages of forest regeneration (5, 20, and 60 years). I found no significant differences between digestible energy available from fruit and forbs when comparing between post-harvest and post-fire stands within any age-class. These results provide evidence that harvested areas can potentially act as surrogates to wildfires in relation to grizzly bear food supply and could thus be used as a means to support ongoing population recovery efforts if human-caused mortality can be controlled. Next, I explored the degree to which grizzly bears may trade off foraging strategies (food resource heterogeneity, defined as both the distribution in digestible energy and variability in digestible energy quality, and homogeneity, defined as digestible energy density) depending on how food resources are spatially allocated and investigated these patterns on seasonal habitat selection for food resources. In general, models that included heterogeneity coupled with homogeneity were most supported and best explained grizzly bear habitat selection across all seasons. Most importantly however, results suggest that bears may alternate between foraging strategies (heterogeneity vs. homogeneity) given they were more likely to use high contrast areas (patchiness) when digestible energy (food) is more widely distributed, and conversely, use resource dense areas when digestible energy distribution is constrained. Finally, I built a novel spatially explicit individual-based model (IBM) that simulates the interaction between grizzly bear agents, a spatiotemporal dynamic landscape of key grizzly bear foods, and differing road density levels for a threatened grizzly bear population in Alberta, Canada. Results suggest that a tradeoff between health and survival may be occurring given the survival rate of bear agents peaked at body condition index values near zero (i.e., when survival was influenced by both road density and low body condition index values). Bear agents that tended to be located in resource poor areas had higher survival rates (areas of low human disturbance) yet were in lower body condition, whereas the opposite pattern occurred in resource rich areas. Lastly, the model showed that the relationship between displacement and body condition index was contingent on whether bear agents foraged in resource rich or poor areas. Collectively, the findings of this thesis contribute to a growing body of literature showing that by shifting the quality, abundance, and distribution of food resources (via landscape change and large-scale disturbances), such disturbances may benefit a threatened bear population by increasing access to high-quality foods in human-modified areas. In turn, this can influence overall health, and ultimately reproduction and fitness, if mortality risk is lowered. Further, the results of this thesis could be used and expanded upon to inform grizzly bear management practices in Alberta, especially under persistent landscape change.</p>