Population fragmentation and inter‐ecosystem movements of grizzly bears in western Canada and the northern United States

Abstract

Population fragmentation compromises population viability, reduces a species ability to respond to climate change, and ultimately may reduce biodiversity. We studied the current state and potential causes of fragmentation in grizzly bears over approximately 1,000,000 km2 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 primary 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‐factorial correspondence analysis (to identify population divisions or fractures with no a priori assumption of group membership), and population‐assignment methods to detect individual migrants between immediately adjacent areas. These data corroborated 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 mountains of British Columbia (BC) and the Yukon. These results contrasted with the spatial pattern of fragmentation in more southern parts of their distribution. Near the Canada–US border area, we found extensive fragmentation that corresponded to settled mountain valleys and major highways. Genetic distances across developed valleys were elevated relative to those across undeveloped valleys in central and northern BC. In disturbed areas, most inter‐area movements detected were made by male bears, with 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 consider 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‐km2 area in southeastern BC, western 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 linear 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 movement rates dramatically when settlement increased to >20% of the fracture zone. At this same threshold, male movement declined more gradually, in response to increased traffic and further settlement. In highly settled areas (>50%), both sexes had a similar reduction in movements in response 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 populations are not viable over the long term. The persistence of this regional female fragmented metapopulation likely will require strategic connectivity management. We therefore recommend enhancing female connectivity among fractured areas by securing linkage‐zone habitat appropriate for female dispersal, and ensuring current large source subpopulations remain intact. The fragmentation we documented may also affect 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.

Moving in the Anthropocene: Global reductions in terrestrial mammalian movements

“…Future landscape management should include animal movements as a key 309 conservation metric and aim towards maintaining landscape permeability. Ultimately, because of 310 the critical role of animal movement for human-wildlife coexistence (29) and disease spread (30), 311 effects of reduced vagility may go beyond ecosystem functioning and directly affect human well-312 Tables S3 for details We compiled GPS location data for 57 mammalian species, comprising 7 339 376 locations of 803 individuals from 1998 to 2015 (Fig. 1, Supplementary Table S1).…”

Factors influencing detection of grizzly bears at genetic sampling sites

“…) Movements Grizzly bears from the South Rockies of BC have been detected north in Banff National Park, south into Montana and east into Alberta. DNA studies began in this ecosystem in 1996 and several thousand bears have been genotyped since that time (see Proctor et al 2010Proctor et al & 2012 for an overview of these projects). Movements among study areas across years are common however movements between individual simultaneous inventories are not common.…”

“…The grizzly bear population of the southern Rocky Mountains in BC and Alberta connects the grizzly bear population to the south in the Northern Continental Divide Ecosystem of Montana with the continuous population further north because the areas to both the east and west are not occupied by bears (Proctor et al 2012). This population has presented several conservation challenges for population managers because: i) coals mines have removed habitat and create broad scale disturbance which may decrease bear use of the remaining or reclaimed habitats, ii) Hwy 3 and associated settlement and development runs east-west across the area which impede north-south movement and may compromise demographic rescue, iii) mortality of problem bears is high and, iv) the CP railway also splits the area north-south and is an increasing source of mortality.…”

“…Many bears were analyzed at more than 9 loci for a population genetics study (Proctor et al 2012). The above methods ensured that individuals identified based on genotypes were nearly certain to assign to a single individual and not a close relative.…”

Home range, movements, and denning chronology of the Grizzly Bear (<em>Ursus arctos</em>) in west-central Alberta

“…We focused on two genetically distinct Grizzly Bear populations in west-central Alberta (Proctor et al 2012): the Yellowhead population unit (YPu; 53°14'53"n, 117°25'12"W) and the Grande Cache population unit (GCPu; 44°10'19"n, 77°13'44"W). the location of the YPu includes southern Jasper national Park in the Rocky Mountains (Figure 1).…”