SEX-BIASED DENSITY-DEPENDENT MIGRATION IN A METAPOPULATION OF THE BUTTERFLY PROCLOSSIANA-EUNOMIA

Current metapopulation models assume that migration rate remains const ant from one generation to the other, leading to a constant population foundation rate. In the butterfly Proclossiana eunomia, the mating be haviour is a main factor affecting individual migration. In a field st udy, male harrassments induced female emigration at high male density. Simulation, ed away in search of mates at low female density. Simulat ions of male-female movements based on behavioural data from the field revealed that changes in mate density will induce sex-biased emigrati on. assessment of migration within a metapopulation in the field durin g 2 years supported these predictions. Such bias in migration has been reported earlier in other butterfly species with a similar mating sys tem. Consequences of sex-biased emigration on metapopulation dynamics may be spasms in population foundation as these occur only when densit y oversteps a certain threshold. Patterns of colonization in a region where P. eunomia did not occur naturally correspond to this prediction . Variability in the rates of emigration and population foundation bet ween generations may affect metapopulation viability analysis by curre nt models. (C) Elsevier, Paris.