Population fragmentation compromises population viability, reduces a species ability to respond to
climate change, and ultimately may reduce biodiversi ty. We studied the current state and potential causes of
fragmentation in grizzly bears over approximat ely 1,000,000 km of western Canada, the northern United States
(US), and southeast Alaska. We compiled much of our data from projects undertaken with a variety of research
objectives including population estimation and trend, landscape fragmentation, habitat selection, vital rates, and
response to human development. Our prim ary analytical techniques stemmed from genetic analysis of 3,134 bears,
supplemented with radiotelemetry data from 792 bears. We used 15 locus microsatellite data coupled with measures
of genetic distance, isolation-by-distance (IBD) analysis, analysis of covariance (ANCOVA), linear multiple
regression, multi-factor ial correspondence analysis (to identify popu lation divisions or fractures with no a prioriassumption of group membership), and population-assignment methods to detect individual migrants between
immediately adjacent areas. These data corro borated observations of inter-area movements from our telemetry
database. In northern areas, we found a spatial genetic pattern of IBD, although there was evidence of natural
fragmentation from the rugged heavily glaciated coast mountain s of British Columbia (BC) and th e Yukon. These
results contrasted with the spatial pattern of fragmentation in more southern parts of their distrib ution. Near the
Canada–US border area, we found extensive fragmentation th at correspo nded to settled mountain valleys and m ajor
highways. Genetic distances across developed valleys were elevated relative to those across unde veloped valleys in
central and northern BC. In disturbed areas, most inter-area movements detected were made by male bears, w ith
few female migrants identified. North–south movements within mountain ranges (Mts) and across BC Highway 3
were more common than east–west movements across settled mountain valleys separating Mts. Our results suggest
that relatively distinct subpopulations exist in this region, including the Cabinet, Selkirk South, and the decades-
isolated Yellowstone populations. Current movement rates do not appear sufficient to consid er the subpopulations
we identify along the Canada–US border as 1 inter-breeding unit. Although we detected enough male movement to
mediate gene flow, the current low rate of female movement detected among areas is insufficient to provide a
demographic rescue effect between areas in the immediate future (0–15 yr). In Alberta, we found fragmentation
corresponded to major east–west highways (Highways 3, 11, 16, and 43) and most inter-area movements were made
by males. Gene flow and movement rates between Alberta and BC were highest across the Continental Divide
south of Highway 1 and north of Highway 16. In the central region between Highways 1 and 11, we found evidence
of natural fragmentation associated with the extensive glaciers and icefields along the Continental Divide. The
discontinuities that we identified would form appropriate boundaries for management units. We related sex-specific
movement rates between adjacent areas to several metrics of human use (highway traffic, settlement, and human-
caused mortality) to understand the causes of fragmentation. This analysis used data from 1,508 bears sampled over
a 161,500-km area in southeastern BC, west ern Alberta, northern Idaho, and northern Montana during 1979–
2007. This area was bisected by numerous human transportation and settlement corridors of varying intensity and
complexity. We used multiple linea r regression and ANCOVA to document the responses of female and male bears
to disturbance. Males and females both demonstrated reduced movement rates with increasing settlement and
traffic. However, females reduced their movem ent rates dramatically when settlem ent incre ased to >20%ofthe
fracture zone. At this same threshold, male movement declined more gradually, in response to increased traffic and
further settlement. In hig hly settled areas (>50%), both sexes had a similar reduction in movements in respons e to
traffic, settlement, and mortality. We documented several small bear populations with male-only immigration,
highlighting the importance of investigating sex-specific movements. Without female connectivity, small pop-
ulations are not viable over the long term. The persistence of this regional female fragmented metapopulation likely
will require strategic connectivity management. We therefore recommend enhanci ng female connectivity among
fractured areas by securing linkage-zone habitat appropriate for female dispersal, and ensuring current large source
subpopulations remain intact. The fragmen tation we documented may also aff ect other species with similar
ecological characteristics: sparse densities, slow reproduction, short male-biased dispersal, and a susceptibility
to human-caused mortality and habitat degradation. Therefore, regional inter-jurisdictional efforts to manage
broad landscapes for inter-area movement will likely benefit a broad spectrum of species and natural processes, particularly in light of climate change. 2011 The Wildlife Society.
