Genetic variation on the rocks - the impact of climbing on the population ecology of a typical cliff plant.
Rock climbing enjoys enormous popularity world-wide. As a consequence, the anthropogenic pressure on the vegetation of formerly undisturbed cliff ecosystems is continuously increasing. The impact of rock climbing on population structure and genetic variation of the rare plant species Draba aizoides was investigated representatively for many other typical central European cliff plants. Populations from eight climbed and from eight pristine cliffs were compared through the use of vertical transect analyses and molecular markers. Population structure differed between climbed and pristine cliffs. Individuals of D. aizoides were significantly smaller and less frequent on climbed compared with pristine cliffs. On plateau sites, the species' occurrence was unaffected by climbing activities; it was significantly less frequent on the faces, but more frequent on the tali of climbed in comparison with pristine cliffs. Genetic variation was greater in populations from climbed compared with pristine cliffs, and genetic differentiation was stronger between subpopulations from pristine cliffs than between subpopulations from climbed cliffs. Synthesis and applications. Rock climbing clearly affects population structure and genetic variation of D. aizoides. Seed dispersal is presumably enhanced by rock climbers but climbers remove and drop plant individuals from cliff faces, which causes a downward shift in population structure. This shift in turn reduces genetic differentiation between upper and lower subpopulations. In mountain regions that attract sport climbing, conservation management plans should therefore always ensure the provision of completely unclimbed cliffs to protect the native vegetation.