Genetic variation and plant performance in fragmented populations of globeflowers (Trolliuseuropaeus) within agricultural landscapes

The management of remnant populations in highly fragmented landscapes requires a thorough understanding of the processes shaping population persistence. We investigated relationships between population characteristics (i.e. size, density and pollinator abundance), offspring performance, genetic diversity and differentiation in Trolliuseuropaeus, a plant with a nursery pollination system. In 19 populations of different sizes and located in north-east Switzerland, an area which has undergone widespread land use changes over the last decades, we assessed neutral genetic diversity (Ntotal = 383) using AFLPs and plant performance in a greenhouse experiment (Ntotal = 584) using competition and control treatments. Overall genetic differentiation was low (FST = 0.033) with a marginal significant isolation by distance effect (P = 0.06) indicating (historical) genetic connectivity among the populations. Mean expected heterozygosity was HE of 0.309 (0.0257–0.393) while inbreeding coefficients (FIS) were significant in only three populations. Genetic diversity was not related to population size, plant density or pollinator abundance. Plant performance was reduced under competition (P < 0.001) but the severity of competition was independent of genetic diversity and population size. In summary, remnant populations of T. europaeus retain genetic diversity and seem capable of persisting under the present conditions within an agricultural matrix. T. europaeus is a perennial herb, thus it may require several generations for the negative effects of fragmentation and isolation to manifest. Our findings indicate that small populations are as important as large populations for the conservation and management of genetic resources.