Partial migration behavior is common across taxa despite evolutionary logic that differential demographic consequences could fix for particular strategies in each system. Woodland caribou in the Canadian Rockies exhibit genetic evidence of mixed lineages of diverged Beringian-Eurasian migratory caribou and North American sedentary caribou subspecies. While both behaviors remain in Canadian Rockies populations, the selective balance between sedentary and migratory strategies may be subject to recent alteration by anthropogenic habitat fragmentation, as mediated by predation. We used Cox proportional hazards modeling to assess the relative impact of migratory behavior, genetic signature, and habitat fragmentation on survival of a sample of >300 radio-marked caribou from 1998-2008.
Results/Conclusions Migratory caribou in these populations exhibited westward seasonal shifts to alpine summer ranges, theoretically to reduce predation risk relative to sedentary individuals that remained year-round in lower-elevation foothills. Human disturbance from wood, oil and gas extraction industries has fragmented forests disproportionately on caribou winter ranges. Fragmentation was correlated with decreased survival over both time and space. While survival probabilities were initially lower for migratory individuals, this balance shifted throughout the study period. Annual survival probability decreased for all caribou across the study period, but this decrease was proportionately greater for sedentary individuals. Spatial population structure was predictive of survival, and trends in local population viability were correlated with the degree of fragmentation. These effects have implications on the long term persistence and behavioral plasticity among threatened woodland caribou populations.
