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 processes such as seed production and cause reductions in fitness, but their relative effects are likely to depend on the life history of the species concerned (i.e. breeding system, dispersal syndrome and longevity). In 14 isolated, remnant populations of the short-lived Leucochrysum albicans subsp. albicnns var. tricolor (Astcraceae), where reproductive population size differed from 74 to over 50,000 flowering plants, seed set and germinability was determined for one flowering season. The breeding system was determined in a hand-cross versus self-pollination experiment in the glasshouse, whilst mating system parameters were determined by molecular methods for four sires spanning the range of reproductive population sizes. Leucochrysum albicnns subsp. albicnns var. tricolor is a self-incompatible species and outcrossing rates were uniformly high (> 90%) in the populations observed. Seed production was not linearly associated with log (population size), although there was substantial within and between-population variability. Seed germinability was rapid and substantial(> 80%) in all populations and not linearly associated with log (population size). This study suggests that (previously identified) short-term factors, such as the maintenance of habitat and safe sites for regeneration, are of immediate importance to the persistence of all L. albicans subsp. albicans var. tricolor populations. To uncouple the effects of population size and within-site factors on plant demography in fragmented plant populations, more research effort should be directed at quantifying the significance of the local-scale interactions that occur between individual plants, pollinators and site environmental factors. (C) 2001 Elsevier Science Ltd. All rights reserved.