Spatial structure of lemming populations (Dicrostortyx groenlandicus) fluctuating in density

The pattern and scale of the genetic structure of populations provides valu able information for the understanding of the spatial ecology of population s, including the spatial aspects of density fluctuations. In the present pa per, the genetic structure of periodically fluctuating lemmings (Dicrostony x groenlandicus) in the Canadian Arctic was analysed using mitochondrial DN A (mtDNA) control region sequences and four nuclear microsatellite loci. Lo w genetic variability was found in mtDNA, while microsatellite loci were hi ghly variable in all localities, including localities on isolated small isl ands. For both genetic markers the genetic differentiation was clear among geographical regions but weaker among localities within regions. Such a pat tern implies gene now within regions. Based on theoretical calculations and population census data from a snap-trapping survey, we argue that the obse rved genetic variability on small islands and the low level of differentiat ion among these islands cannot be explained without invoking long distance dispersal of lemmings over the sea ice. Such dispersal is unlikely to occur only during population density peaks.