Coexistence between humans and carnivores relies on connectivity to wilderness areas to sustain wildlife populations. Credit: Darryn Epp
Connectivity is deeply embedded in the conservation lexicon. Between efforts to help animals safely cross roads or the creation of regional-scale linkage plans, enhancing connectivity is a fundamental approach to reducing the negative impacts of a changing landscape on biodiversity. But the picture on the ground isn’t so clear, especially when it comes to large carnivores. How exactly does connectivity affect conflict between people and wildlife?
Following decades of suppression, carnivores are now expanding and occupying human-dominated areas (for example, in Europe, the Midwest USA, the Canadian Prairies, and India). This recovery has sparked an important debate regarding the role of wilderness and connectivity in facilitating coexistence with carnivores.
We recently published a paper to add further insights in this debate. We put together a long-term (40 year) and spatially expansive (370,000 km2) dataset including >2,500 brown bears (Ursus arctos), one of the world’s most widely distributed and conflict-prone carnivores. We tracked animal movements, and conducted spatial capture-recapture analyses to document the survival, dispersal, and age-related shifts in nocturnality.
A basin of coexistence for humans and brown bears near Creston, Bristish Columbia, Canada. From Clayton et al. (2020) PNAS.
We document staggering lethality of bears living in human modified landscapes. In rural areas where bears and people regularly co-occur, there was ~ 51 dead bears for every successful coexistor (i.e. bears surviving to age 11, when their probability of survival peaks). In contrast, in a wilderness area only 3.5 bears will die for every bear that lives to age 11. Moreover, we found that coexisting bears must shift to ~80% nocturnality. We document no consistent pattern of nocturnality of bears in wilderness areas.
How do bear populations persist under such high rates of mortality? The answer is connectivity.
Our paper introduces the concept of a ‘basin of coexistence’ – the spatial extent of heightened mortality near human-influenced areas. Coexistence inside the basin requires immigration from areas with lower human activity. As such, wilderness is a vital component of ‘front country’ coexistence.
For bears, the basin of coexistence radiates outwards up to 80 km from towns, roads, and agricultural areas, meaning that the actual impact of people is far greater than the footprint of roads and buildings alone. Indeed, the basin of coexistence influences the behavior and immigration patterns of ~40% of the southern part of the bears’ North American range. There are over a million people living in the brown bears basin of coexistence.
Our study reveals a striking paradox of carnivore coexistence: the mobility of brown bears through the landscape condemns individual animals to death by people, yet rescues populations from extirpation. Unless and until people change the lethality of human-occupied landscapes, connectivity will remain an essential component of coexistence.