Conclusions:
Grizzly bear population fragmentation corresponded to the presence of settled mountain valleys and major highways. In these disturbed areas, the inter-area movements of female bears was affected more than for male bears. Without female connectivity, small subpopulations of grizzly bears are not viable over the long term.
Thresholds/Learnings:
Females grizzlies reduced their movement rates drastically when settlement increased to >20% of a given area. In highly settled areas (>50% settlement), both sexes demonstrated similar reductions in movement.
Synopsis: Researchers studied the current state and potential causes of population fragmentation in grizzly bears over western Canada, the Greater Yellowstone region of the United States, and southeast Alaska. In less settled northern regions, the study found that spatial genetic patterns of isolation-by-distance (IBD) are caused largely by natural fragmentation from the rugged glaciated terrain. These results contrasted with spatial patterns of fragmentation found in the southern parts of the study area. Near the US-Canada border, population fragmentation corresponded to the presence of settled mountain valleys and major highways. In these disturbed areas, most inter-area movements were recorded in male bears. North-south movements within mountain ranges were more common that east-west movements across settled mountain valleys. In Alberta, fragmentation corresponded to east-west highways. Both males and females demonstrated reduced movement rates with increasing settlement and traffic, however females reduced their movement rates drastically when settlement increased to >20% of the fracture zone. In highly settled areas (>50%), both sexes demonstrated similar reductions in movement. The results of this study indicate that, without female connectivity, small subpopulations of grizzly bears are not viable over the long term. Enhancing female connectivity among fractured areas by securing linkage-zone habitat appropriate for female dispersal is key to guaranteeing the persistence of fragmented metapopulations.
