Reproductive success does not decline in fragmented populations of Leucochrysum albicans subsp albicans var. tricolor (Asteraceae)

Fragmentation and isolation of plant populations can affect demographic pro cesses such as seed production and cause reductions in fitness, but their r elative effects are likely to depend on the life history of the species con cerned (i.e. breeding system, dispersal syndrome and longevity). In 14 isol ated, remnant populations of the short-lived Leucochrysum albicans subsp. a lbicnns var. tricolor (Astcraceae), where reproductive population size diff ered from 74 to over 50,000 flowering plants, seed set and germinability wa s determined for one flowering season. The breeding system was determined i n a hand-cross versus self-pollination experiment in the glasshouse, whilst mating system parameters were determined by molecular methods for four sir es spanning the range of reproductive population sizes. Leucochrysum albicn ns subsp. albicnns var. tricolor is a self-incompatible species and outcros sing rates were uniformly high (> 90%) in the populations observed. Seed pr oduction was not linearly associated with log (population size), although t here was substantial within and between-population variability. Seed germin ability was rapid and substantial(> 80%) in all populations and not linearl y associated with log (population size). This study suggests that (previous ly identified) short-term factors, such as the maintenance of habitat and s afe sites for regeneration, are of immediate importance to the persistence of all L. albicans subsp. albicans var. tricolor populations. To uncouple t he effects of population size and within-site factors on plant demography i n fragmented plant populations, more research effort should be directed at quantifying the significance of the local-scale interactions that occur bet ween individual plants, pollinators and site environmental factors. (C) 200 1 Elsevier Science Ltd. All rights reserved.