A MODELING STUDY OF THE POPULATION-DYNAMICS OF A LARGE BLUE BUTTERFLY, MACULINEA-REBELI, A PARASITE OF RED ANT NESTS

1. The five European species of Maculinea butterflies are among the most endangered invertebrates in the world. To attain a better understanding of the mechanisms which are most influential to their population dynamics, we develop a mathematical population model for one of these species, Maculinea rebeli, based on its dependence on two sequential resources, the cross-leaved gentian, Gentiana cruciata, and a red ant, Myrmica schencki. One of the main objects of this modelling study is to raise questions about the ecology and conservation of this rare and fascinating butterfly. 2. The model has two main biological components: (i) recruitment and competition on the plant for the first few weeks of butterfly life, and (ii) recruitment by and competition within nests of the red ant for the remainder of the butterfly life-cycle. 3. We estimate all of the parameters for the model based in part on data collected at a 4-ha study site in the Spanish Pyrenees, one of the largest known populations of Maculinea in the world. 4. The model is used to evaluate how different ecological processes and densities of the plant and ant resources may affect the butterfly population, including its density, resilience from perturbation. and persistence. 5. The model clearly indicates that, for the Spanish study site, the survival of the butterfly in ant nests is disproportionately more important to its population than is competition on the plant. Changes in the observed population of the plant have virtually no impact on the butterfly population. 6. Future studies should take account for instance of changes in the density of ant nests and the population of a specialist ichneumonid parasitoid.