Effects of population size on genetic diversity, fitness and pollinator community composition in fragmented populations of Anthericum liliago L.

The genetic and fitness consequences of habitat fragmentation on the dry grassland species Anthericum liliago L. (Anthericaceae) were examined. We used random amplified polymorphic DNA (RAPD) markers to determine the distribution of genetic diversity within and among 10 German A. liliago populations, ranging in size from 116 to over 2 million ramets. The genetic diversity of an A. liliago population was highly positively correlated with its population size. The overall differentiation among populations (Phi-ST = 0.41, P < 0.0001, AMOVA) was considerably higher than expected for a species with a mixed breeding system. No strong correlation (P < 0.01) was detected between fitness parameters and population size and genetic diversity. The reproductive output (seeds per ramet) was only highly correlated (P < 0.001) with the proportion of flowering ramets in a population which could be caused by a more effective pollination in large populations which are more attractive to specialized pollinators. The specialized A. liliago pollinator Merodon rufus (Syrphidae) and high abundances of solitary bees could only be found in A. liliago populations with more than 10,000 individuals. Genetic differentiation among the investigated A. liliago populations may have been caused by limited seed and pollen dispersal and a mixed mating system permitting a high selfing rate. The differentiation among the small and isolated populations lacking main pollinators seems to be caused by genetic drift.