This conclusion was, however, based on comparisons of within-species variation among different taxa which probably also differ in other aspects like geographic location, population history, mutation rates and population structure, all of which potentially affect genetic variation (Hague and Routman 2015). In contrast, mitochondrial DNA (mtDNA) variation did not reflect population size, probably as an effect of selection acting on mtDNA. From this comprehensive study they found that nuclear sequence data showed results consistent with the expectation of more genetic variation in abundant species. ( 2006) studied genetic polymorphisms in approximately 3000 animal species. Although the relationship between population size and genetic variability is well-known and supported by empirical data across different taxa (see Frankham 1996 for review), the reality of this relationship may also be questioned (Amos and Harwood 1998 Bazin et al. Thus genetic erosion of small populations has become a major conservation concern, as low levels of variation is considered limiting to the ability for populations to respond to changed environmental conditions as well as threats like diseases, parasites and predators (Amos and Harwood 1998). Population genetic theory predicts that small populations have less variation compared to large populations due to genetic drift and inbreeding (Hartl and Clark 1997).
Among the many possible consequences of fragmentation, is delimited spatial patterns of dispersal and reproduction, which in turn may lead to reduced levels of within-population genetic variation and alterations of spatial genetic structure (Young et al.
Whereas habitat loss has large, consistently, negative effects on biodiversity, habitat fragmentation effects may be subtle, scale-dependent, and can be negative or in some cases even positive (review in Fahrig 1997, 2003, 2013 Tischendorf et al.
Large-scale landscape changes are intimately linked to habitat loss and fragmentation, and pose major threats to biodiversity where many populations are declining, and many species are currently at the brink of extinction (Frankham et al. To sustain viable populations, conservation strategies should focus on genetic connectivity between populations. Our results imply that the genetic structure of Norwegian wild reindeer is mainly driven by recent colonization history, population size, as well as human-induced landscape fragmentation, restricting gene flow and leading to high levels of genetic drift. We found high levels of differentiation among most populations, indicating low levels of gene flow, but only a weak correlation between geographic and genetic distances. This relationship was positive and linear until a threshold for population size was reached at approximately 1500 reindeer. The microsatellite data indicated a relationship between population size and genetic variation. Overall, both markers showed highly varying levels of genetic variation, with reduced variation in the smaller and more isolated populations.
As a basis for future management strategies we assess genetic structure and levels of genetic variation in Norwegian wild reindeer by analysing 12 microsatellite loci and the mitochondrial control region in 21 management units with varying population sizes. The number and continued presence of wild reindeer have been significantly reduced due to accelerating anthropogenic habitat modifications, as well as displacement in benefit of domesticated herds of the species. As a migratory species requiring large living areas, wild reindeer ( Rangifer tarandus) is highly vulnerable to human activity. These changes may further lead to depletion of genetic variation within populations as well as accelerating differentiation among populations. Landscape changes, such as habitat loss and fragmentation, subdivide wild populations, reduce their size, and limit gene flow.
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