Understanding population history for conservation purposes: Population genetics of Saxifraga aizoides (Saxifragaceae) in the lowlands and lower mountains north of the Alps

Several alpine species have outlying populations in the lowlands and lower mountains north of the Alps. These small, isolated populations are usually described as either (1) glacial relies, (2) descendants from populations li ving on forelands and moraines during the ice ages, or (3) populations foun ded by long-distance dispersal after glaciation. A floristic survey of the historic and present distributions and an allozyme investigation were perfo rmed on one of these relic species, Saxifraga aizoides. The species was his torically more abundant and had more stations in more regions of northeaste rn Switzerland. The former population structures within regions, nowadays d estroyed, were still reflected in distinct and high regional genetic divers ity and variation. There was weak evidence of increased inbreeding in outly ing populations, but populations did not deviate from Hardy-Weinberg equili brium. No geographic pattern of genetic variation above the regional scale (>10 km) was found. Based on the spatial and genetic structures found, it w as not possible to discriminate between the abovementioned hypotheses. Neve rtheless, the study shows how a thorough evaluation of distribution and abu ndance data aids the interpretation of genetic data with respect to populat ion history, biogeography, and conservation biology.