Genetic analysis of movement, dispersal and population fragmentation of grizzly bears in southwestern Canada
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AbstractI studied dispersal and inter-population movement of grizzly bears near the southern extent of their North American range in southwestern Canada and northwestern U.S.A. This area represents the interior portion of the southern edge of grizzly bear distribution following 100 years ofrange contraction. Fragmentation, as a result of the increasing human presence, is influencing ecosystems around the globe. I address whether anthropogenic fragmentation has affected grizzly bear populations in this vulnerable area. Human attitudes toward grizzly bears, and large carnivores in general, have experienced a paradigm shift from active persecution towards tolerance and respect. However, major forces underpinning range contraction including human-caused mortality and fragmentation, may be still operating, albeit, more subtly and less intentionally. Checking further range contraction requires specific knowledge of the processes at work. Improvements have been made in managing and monitoring human-caused mortality, however, besides the obviously isolated populations ( e.g. Yellowstone National Park), the status of fragmentation in this region was largely unknown. My goals were to use genetic analyses to explore bear movement and dispersal within and between the relictually occupied mountain ranges in southwestern Canada. I genetically sampled and generated 15-locus micro satellite genotypes for 83 5 bears across approximately 100,000 km2 in immediately adjacent geographic areas. I used population assignment techniques, parentage analysis, cluster analysis, multiple linear regression and several matrices of population genetics. I present evidence of natural and human-caused fragmentation, identify fragmenting forces, establish population and sub-population boundaries in the region, identify small vulnerable sub-populations, describe dispersal behaviour, and discuss factors that make bears susceptible to fragmentation. Female movement was restricted by human transportation and settlement corridors, and male movement appeared to be reduced in some areas. Fragmentation by north/south oriented major human-settled valleys and the major east/west transportation corridors have left much of the area a partially :fragmented set of local sub-populations varying in size and intensity of fragmentation. I found one small isolated population (n < 100) in the southern Selkirk Mountains, several small sub-populations (n < 100), including several "female demographic islands" and several population sub-units that were relatively large (n > 300). Through multiple linear regression, I implicate human settlement patterns, human-caused mortality, and traffic volumes as inhibiting rates of inter-population movement. I also measured dispersal distances of grizzly bears and found that males, on average, dispersed approximately 46 km and females 14 km, a result similar to previous radiotelemetery findings for the region. Because several fragmented sub-units are small, maintaining regional connectivity may be necessary to ensure persistence. Despite grizzly bear vagility, their conservative dispersal behaviour and difficulty in living close to humans, make maintenance of regional connectivity challenging.
Bibliography: p. 131-147