Northern boreal caribou conservation should focus on anthropogenic disturbance, not disturbance-mediated apparent competition

Abstract

Understanding the relative importance of threats to species across their range is critical for large-scale conservation planning. Scaling-up localized research to inform the Canada-wide boreal caribou (Rangifer tarandus caribou) recovery strategy epitomizes the challenge. Current policy draws heavily from data obtained at the southern front of range retraction. Here, disturbances benefiting early successional herbivores (e.g., moose [Alces alces]), and hence wolves (Canis lupus) imparts increased predation risk to caribou (via “disturbance-mediated apparent competition” [DMAC]). Anthropogenic linear features (e.g., corridors, roads etc.; LFs) also improve wolf hunting efficiency, exacerbating DMAC, with caribou thereby losing functional habitat. However, ~2/3 of extant caribou range occurs in northern Canadian Shield and Taiga habitat, which contrasts with southern areas in both disturbance regime (fire-dominated) and community assembly (e.g., no deer [Odocoileus spp.]). To test predictions of DMAC and LF-avoidance in a northern caribou population (Saskatchewan Boreal Shield; ~3% of habitat within 500 m of anthropogenic disturbance), we tracked 94 GPS-collared females (2014–2018). Unexpectedly, caribou did not avoid LFs at most scales of observation. Although they responded to vegetation in line with apparent competition, resiliency of conifer-dominated successional trajectories and muted moose-wolf responses to disturbance suggest that poor primary productivity may modulate the strength of DMAC to caribou—including its potential interaction with LFs to influence movements. Before focusing on DMAC as the principal threat to caribou in northern ecoregions, further studies investigating if caribou and predators functionally respond to increasing LF-availability are needed, as it may be most critical for conserving crucial source populations.