Metapopulation dynamics of the bog fritillary butterfly: demographic processes in a patchy population

Metapopulation models predicting the persistence of species on the verge of extinction in fragmented landscapes have to include local population dynamics. In this paper, we report on a 9-yr study in which a patchy population of the bog fritillary was monitored each year, with special focus on quantifying demographic parameters. We parameterised various constrained linear models (CLM) with capture-mark-recapture (CMR) data collected in the field each year and we tested the effects of several variables on demographic parameters. Selecting the best CLM, we estimated the mean and the variance of (1) individual parameters (survival and catchability) and (2) population features (population size, sex-ratio and recruitment). Survival was not related to the age of the individual but decreased continuously during the flight period, which means that lifetime expectancy is conversely related to the delay between the moment of the emergence of a given individual as compared to the emergence of the first adult in the population. Survival was lower in males than in females, as a consequence of male mate-locating behaviour. Daily population size fits a parabolic distribution in both sexes, males appearing, reaching their abundance peak and dying before females. Yearly variation in the sex-ratio is the consequence of the between-sex difference in the recruitment curve. Total adult population size shows large variations between years. Analysis of the relation between growth rate and abundance indicates density dependence, probably related to parasitism of the larval stages. Density at the equilibrium is about 200 adults/ha.