Grizzly bear populations are facing negative impacts from human activities, according to research published in Wildlife Monographs. These impacts include both top-down factors, such as direct mortality linked to forestry roads (due to conflicts or illegal killings) and displacement from high-quality habitats, as well as bottom-up factors like reduced availability of food resources.
The study, conducted in southeastern British Columbia, involved the radio-collaring and monitoring of numerous grizzly bears over several years. It revealed an intriguing relationship between the most significant bottom-up factor, the availability of huckleberry patches (a critical food resource for grizzly bears), and mortality risks associated with forestry roads (road density and the distance to secure habitats away from roads).
The research demonstrated that top-down influences were not only connected to mortality risk but also limited the accessibility of critical food resources. This limitation had adverse effects on female grizzly bear fitness and population density, essentially mirroring the impacts of habitat loss. The combined negative effects of both top-down and bottom-up factors contribute to the widespread challenges faced by grizzly bear populations in western North America, particularly in areas with high forestry road density.
The study’s findings emphasize the importance of considering both top-down and bottom-up influences when assessing the factors affecting wildlife populations. According to lead author Michael Proctor, PhD, from Birchdale Ecological Ltd., securing critical bear food resources requires some level of human access restriction. These results suggest that the benefits of essential bear foods are not fully realized unless human access to nearby roads is reduced.
In summary, the study underscores the need for conservation efforts that address the complex interplay of factors affecting grizzly bear populations, including both their habitat and the human activities that impact them.
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