Patch occupancy, population size and reproductive success of a forest herb (Primula elatior) in a fragmented landscape.

Forest fragmentation is expected to affect patch occupancy patterns, population size and population viability of plant populations through changes in both patch area and isolation. We tested the hypothesis that patch area has had a significant effect on patch occupancy and population size of Primula elatior, a common forest herbaceous plant species in Flanders, Belgium. The hypothesis that plants from small populations have lower fitness as reflected by several characteristics related to reproduction was also tested. Finally, the probability of P. elatior colonizing presently empty patches was investigated. Patch area proved to be the most important factor explaining population size. Patch area, spatial isolation and within-patch habitat characteristics all contributed significantly to the explanation of the distribution pattern of P. elatior. Plants from small populations had a significantly lower individual fitness than plants from large populations. Small populations produced significantly fewer seeds per fruit and per plant than did large populations. Individual seed mass decreased with increasing population size, but total seed mass increased with increasing population size. Plant-to-plant variability in the proportion of flowers setting fruit, number of seeds per fruit and number of seeds per plant decreased with increasing population size. Skewed pin-thrum ratios and lower pollination intensity may explain the reduced fecundity in small populations. Geographical isolation had a significant effect on the probability of P. elatior colonizing empty patches. The results show that patch area and isolation may influence regional persistence of plant populations through altered colonization probabilities and reduced reproductive success of small populations.