Genetic variability and minimum viable populations in the Vancouver Island marmot (marmota vancouverensis)
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AbstractFrom 1987 through 1989 I studied four colonies of Vancouver Island mannots (Marmota vancouverensis) to assess genetic variability and population viability in this species. Six family groups at two natural colonies remained remarkably stable throughout the study. Seven family groups at two logging-slash colonies displayed greater turnover of individuals, and comparatively short-term use of burrows. Females produced average litters of 3.2 young (n= 13) every second year, although one bred in consecutive years. Litters of four were more common in "slash" colonies. M. vancouverensis appears to be essentially monogamous, and in other respects exhibits a social structure similar to that of M. olympus. Reproductive and survivorship rates varied dramatically with year, family group, and colony. Marmots using established burrow systems in natural habitats did comparatively well; marmots using new burrow complexes did either very well or very poorly. Most mortality apparently occurred during winter hibernation. Sampled M. vancouverensis (n=44) were neither genetically destitute nor highly inbred. Electrophoresis revealed levels of genetic variability comparable to M. flaviventris and M. monax (n=22 scorable loci, estimated %polymorphic loci P=0.18, average expected heterozygosity H=0.073). Small but significant genetic differences were found between two colonies less than 20 kilometres apart, illustrating the importance of founder effects and infrequent dispersal. Effective population size Ne of the known population is close to 50 (estimates of 34.6 to 64.4). M. vancouverensis is well-adapted to a "meta-population" lifestyle, in which a patchwork of colonies experience periodic extinctions and recolonizations. Small colonies of M. vancouverensis are vulnerable to extinction through random demographic and environmental events. Most known colonies are small. Toe entire population inhabits a geographically confined area, is insufficient to maintain long-term evolutionary potential (Ne=500), and is very close to the size necessary to prevent short-term loss of genetic variability through inbreeding and drift (Ne=50). Toe full effects of humancaused landscape alteration on marmots are not yet understood: I hypothesize that logging-slash may provide attractive summer habitat but poor conditions for successful hibernation, and may therefore act as a "sink" for dispersing marmots from higher elevation natural colonies. I conclude that the known population of M. vancouverensis is not "viable" using existing criteria. Long-term survival of M. vancouverensis requires that additional metapopulations be found or established, and that adequate gene flow between individual colonies be maintained. A three-pronged recovery plan is proposed. Objective #1 is to maintain current numbers and distribution, and to answer basic questions of population biology. Objective #2 is to establish a second meta-population of approximately 200 animals. At this time the species should be downlisted to "threatened" status. Objective #3 is to establish a third meta-population (of approximately 200 animals), at which time the species should be downlisted to "vulnerable" status. Additional research (on hibernacula, dispersal, and survivorship) and inventory efforts are needed. Discovery of new meta-populations could dramatically reduce the need for recovery efforts, but is unlikely.
Bibliography: p. 82-89.