G) was recorded on all plants sampled along two 100 m transects.Appendix B. A detailed escription of the parameter estimation.
The main parameters for G. pneumonanthe are derived from Oostermeijer et al. (1996) . They studied 35 transition matrices from annual collections at 10 different sites seven times over the period 1987–1993. Some parameter estimates were adapted to the parameterization of our model. Plant fecundity and breaking dormancy were higher than in Oostermeijer et al. (1996) , because in our model they correspond to optimal values at the beginning of succession. Entry into dormancy is higher because it corresponds to optimal values at the end of succession. The rate of succession parameter, k, was chosen to fit the pattern observed in the field (Oostermeijer et al. 1994) as assumed in Chapman et al. (1989). The threshold density Gmax was chosen so that the maximal density obtained in the simulations corresponded to maximum densities observed in the field (Oostermeijer et al. 1994) . The average number of flower buds per plant was measured in France (Sarthe) in 1992 in the site where the three species of the community module were present. The area chosen is a grassland of 8500 m2 without any particular management except irregular mowing. The total number of seedpods (G) was recorded on all plants sampled along two 100 m transects.
Descriptions of some M. alcon parameter estimations are given by Thomas et al. (1989, 1991), Thomas and Elmes (1998, 2001), and Schönrogge et al. (2000), but many others (F,
1, 2) have been measured between 1992–1995 in the field from Myrmica scabrinodis-using populations of M. alcon in France (Sarthe). The proportion of caterpillars surviving the first weeks following recruitment into ant nests (3) was chosen by comparison with data available for Maculinea rebeli (Hochberg et al. 1992) . The proportion of caterpillars surviving parasitism by Ichneumon fulvicornis (4) was obtained from rearing M. alcon pupae excavated in the field on 2 sites (Spain, Poland) in mid July.
Myrmica scabrinodis colony growth rates (
A ) has been estimated a posteriori using a modified version of HCET model (Belrose and Hochberg, unpublished results) and the densities of G. pneumonanthe, M. alcon, and Myrmica scabrinodis found in the sites in France (Sarthe) in 1992. The rate of decrease of Myrmica scabrinodis with successional stage, h, was chosen to fit observed field trends (J. A. Thomas, personal observation). Thomas (2002) describes methodology and results in quantifying the mean potential area of worker ant search from Myrmica sabuleti nests (
) and caterpillar recruitment. The threshold density of ant nests was chosen such that realized population size of Myrmica scabrinodis corresponded to values observed in the field ( Dufour 1992; J. Mercier, personal communication; J. A. Thomas, personal observation). Values for the average number of caterpillars per ant nest (A ) were obtained in the field by excavating and dissecting entire Myrmica colonies on two Myrmica scabrinodis-using M. alcon sites in Spain and one in Poland (Thomas and Elmes 1998) , supplemented by laboratory-rearing experiments using techniques described by Elmes et al. (1991) . The strength of parasitism by M. alcon was chosen so that realized population size of Myrmica scabrinodis and M. alcon corresponded to values observed in the field ( Dufour 1992; J. Mercier, personal communication; J. A. Thomas, personal observation).
LITERATURE CITED
Chapman, S. B., R. J. Rose, and R. T. Clarke. 1989. The behavior of populations of the marsh Gentian (Gentiana pneumonanthe) - a modeling approach. Journal of Applied Ecology 26:1059–1072.
Dufour, C. 1992. Approche théorique et expérimentale de la dynamique des populations de Maculinea. Laboratoire d'écologie, U.R.A 258. Master Thesis. Ecole Normale Supérieure, Paris, France.
Elmes, G. W., J. A. Thomas, and J. C. Wardlaw. 1991. Larvae of Maculinea rebeli, a large-blue butterfly and their Myrmica host ants: wild adoption and behaviour in ant-nests. Journal of Zoology 223:447–460.
Hochberg, M. E., J. A. Thomas, and G. W. Elmes. 1992. A modelling study of the population dynamics of a large blue butterfly, Maculinea rebeli, a parasite of red ant nests. Journal of animal ecology 61:397–409.
Oostermeijer, J. G. B., R. Vantveer, and J. C. M. Dennijs. 1994. Population-structure of the rare, long-lived perennial Gentiana pneumonanthe in relation to vegetation and management in the Netherlands. Journal of Applied Ecology 31:428–438.
Oostermeijer, J. G. B., M. L. Brugman, E. R. DeBoer, and H. C. M. DenNijs. 1996. Temporal and spatial variation in the demography of Gentiana pneumonanthe, a rare perennial herb. Journal of Ecology 84:153–166.
Schönrogge, K., J. C. Wardlaw, J. A. Thomas, and G. W. Elmes. 2000. Polymorphic growth rates in myrmecophilous insects. Proceedings of the Royal Society of London B 267:771–777.
Thomas, J. A. 2002. Larval niche selection and evening exposure enhance adoption of a predacious social parasite, Maculinea arion (large blue butterfly), by Myrmica ants. Oecologia 132:531–537.
Thomas, J. A., and G. W. Elmes. 1998. Higher productivity at the cost of increased host-specificity when Maculinea butterfly larvae exploit ant colonies through trophallaxis rather than by predation. Ecological Entomology 23:457–464.
Thomas, J. A., and G. W. Elmes. 2001. Food-plant niche selection rather than the presence of ant nests explains oviposition patterns in the myrmecophilous butterfly genus Maculinea. Proceedings of the Royal Society of London Series B-Biological Sciences 268:471–477.
Thomas, J. A., G. W. Elmes, J. C. Wardlaw, and M. Woyciechowski. 1989. Host specificity among Maculinea butterflies in Myrmica ant nests. Oecologia 79:452–457.
Thomas, J. A., M. L. Munguira, J. Martin, and G. W. Elmes. 1991. Basal hatching by Maculinea butterfly eggs - a consequence of advanced myrmecophily. Biological Journal of the Linnean Society 44:175–184.