Population biology of two rare fern species: long life and long-lasting stability.

Premise Of The Study: This study describes the population dynamics of two rare fern species and evaluates the prospects of their survival. This is the first detailed demography study of ferns using transition matrix models. The study species, Asplenium adulterinum and A. cuneifolium, are restricted to serpentine rocks and differ in ploidy level and partly in habitat requirements. Both species are of interest in nature conservation. •

Methods: Single life-history traits were evaluated and transition matrix models were used to describe the dynamics of the populations. Population growth rates, elasticity values, and life-table response experiments were used to compare the dynamics between species, years, and different habitat types. Predicted population performance based on models was compared with real data on population growth. •

Key Results: All populations of both species are growing. Stable stage distribution based on stochastic simulation corresponds to current stage distribution. The most critical phase of the life cycle is stasis of large adult plants. Reproduction is of low importance. Extinction probability of small populations is low. Mean life span of individuals of both species is 30-50 yr. When compared with real data, the model successfully predicted population performance over 10 yr. •

Conclusion: Populations in the study region are not endangered, and current population dynamics are stable. Differences in life-history traits between species, probability of extinction between species and habitat, and different ploidy-and, thus, probably different dispersal ability-suggest the existence of metapopulation dynamics.