ORIGINAL PAPER Genetic diversity and population differentiation in the endangered Siberian flying squirrel (Pteromys volans) in a fragmented landscape Satu Lampila & Laura Kvist & Ralf Wistbacka & Markku Orell Received: 12 November 2008 / Revised: 18 February 2009 / Accepted: 18 February 2009 / Published online: 4 March 2009 # Springer-Verlag 2009 Abstract Siberian flying squirrel (Pteromys volans) has declined in Finland and it is considered an endangered species. We studied microsatellite variation in four flying squirrel populations in a fragmented landscape in Finland to determine the amount of gene flow and genetic diversity in the populations. Demographic data from these areas suggest that the populations are declining. All the populations are significantly differentiated (F ST =0.23). The most notable result is the high degree of differentiation between two adjacent populations (F ST =0.11) and low genetic variability (number of alleles 3.0) in one of the populations. These findings suggest problems in dispersal and possible fragmentation effects in the landscape where only 10–20% of habitat favorable for the flying squirrel is left. Conser- vation ensuring dispersal should be urgently considered. Future studies should concentrate on the modeling of the population viability and on the effects of inbreeding in these small populations. Keywords Dispersal . Microsatellite . Rodentia . Sciuridae Introduction Habitat loss and fragmentation are a major threat to viability of most of the threatened species worldwide (Baillie et al. 2004), because species adapted to a formerly more connected landscape lack effective migration strate- gies (Hanski 2005). Low colonization ability and narrow tolerance for changes in environmental conditions largely explain decline of many forest species (Hanski 2005). Furthermore, populations living on the edge of their geographical range may be especially vulnerable to frag- mentation because they may not be able to find refuge if the current habitat deteriorates. They are also more likely to face environmental stress than the individuals inhabiting the center of the distribution area. The extinction risk of a species is likely to increase rapidly if habitat availability falls below a general threshold value (Andrén 1994). Hanski (2005) stated that a popula- tion will decline markedly when 10–30% of the original suitable habitat remains. When the amount of suitable habitat is less than 10% of the original, extinction risk will substantially increase. A metapopulation is not viable in a landscape, which is fragmented to small and isolated patches. If the amount of favorable patches decrease, the fraction of inhabited patches tends to decrease as well (Hanski 2005). Population decline reduces genetic variability (Frankham 1996) mainly due to random genetic drift and inbreeding (Garza and Williamson 2001). They have adverse effects on the species’ ability to evolve in response to a changing environment (Reed and Frankham 2003) and many threat- ened taxa suffer from reduced ability to evolve, elevated inbreeding, and reduced reproduction rate (Reed and Frankham 2003). For example, it has been shown that inbreeding depression negatively affects disease resistance Eur J Wildl Res (2009) 55:397–406 DOI 10.1007/s10344-009-0259-2 Communicated by W. Lutz Electronic supplementary material The online version of this article (doi:10.1007/s10344-009-0259-2) contains supplementary material, which is available to authorized users. S. Lampila (*) : L. Kvist : M. Orell Department of Biology, University of Oulu, P. O. Box 3000, 90014 Oulu, Finland e-mail: Satu.Lampila@oulu.fi R. Wistbacka Eteläinen Luodontie 139, 68570 Luoto, Finland