Northern Mountain Caribou (Rangifer tarandus caribou) distributional response to habitat disturbance and altered predator-prey dynamics

Woodland caribou (Rangifer tarandus caribou) across North America are in decline, largely as a result of habitat change that has altered their relationship with other ungulates and their shared predators, a process known as disturbance mediated apparent competition (DMAC). In British Columbia, Northern Mountain Caribou (NMC) are found at the northern limit of expansive human-footprints. Subpopulations at the southern extent of NMC are threatened by habitat disturbance that has led to population decline and has forced caribou into small and isolated alpine areas. At the northern extent of NMC, caribou freely range in large subpopulations in landscapes with minimal anthropogenic disturbance. The contrast between high- and low-disturbance landscapes offered a unique opportunity to study the predator-prey and distribution dynamics of caribou as they relate to habitat disturbance and DMAC. I used Bayesian stable isotope mixing models to understand the diet of wolf (Canis lupus) and grizzly bear (Ursus arctos horribilis), the two main predators of caribou and moose (Alces americanus), their apparent competitor. There was relatively more moose and less caribou in the diet of sampled wolves in the high-disturbance landscapes. That relationship suggested that caribou subpopulations in that portion of the study area were subject to either numeric or spatial DMAC, and that quantitative measure of predator diet may be a useful index of changes in the relative abundance of moose and caribou over time. I used the same contrast in disturbance among landscapes to investigate the relationship between the distribution of 295 GPS-collared female caribou, disturbance, and DMAC. Seasonal home ranges were smaller and caribou used higher elevation habitats when they were confronted with relatively greater area of habitat disturbance. These two results are consistent with observations for other types of mountain caribou and indicate that habitat disturbance and DMAC contribute to range contraction. In total, my study suggests that increases in habitat disturbance will lead to continued range contraction for southern subpopulations of NMC and potentially instigate range contraction in the north. Thus, it is critically important to consider ways to reduce habitat disturbance and proactively safeguard intact habitats across the range of NMC.