Thresholds in the capacity of boreal caribou to cope with cumulative disturbances: Evidence from space use patterns

Boreal caribou, an ecotype of woodland caribou (Rangifer tarandus caribou), are closely associated with the boreal forest, which has been significantly modified by anthropogenic activities over the last century. The species’ response to disturbances has been extensively researched – a reflection of the importance of habitat loss in the decline of boreal caribou. We investigated how female caribou cope with disturbances using GPS telemetry data collected on 48 females in a highly managed landscape in Québec, Canada, between 2004 and 2010, using home-range size as a proxy of caribou space use behaviour. Individuals were found to expand their home ranges as the amount of disturbances in their habitat increased, up to a point where further increase caused home range contraction. The density of major roads and the proportion of clearcuts had an important impact on space use throughout the whole year, but the impact of roads was particularly important during calving, summer and rut, while the impact of clearcuts prevailed in spring, early and late winter. Furthermore, we found that a more convoluted shape of cutblocks amplified the effect of clearcuts on caribou space use. These non-linear responses suggest that there is a limit to the adaptability of caribou in coping with anthropogenic disturbances. Although home range expansion could affect survival through the use of unknown habitats, individuals confined in smaller home ranges could be forced into an ecological trap and be more easily detected by predators, making current disturbance levels in the boreal forest and their cumulative amount in the landscape a major issue for the conservation of these boreal caribou populations.