Sex-biased density-dependent migration in a metapopulation of the butterfly Proclossiana eunomia

Current metapopulation models assume that migration rate remains constant from one generation to the other, leading to a constant population foundation rate. In the butterfly Proclossiana eunomia, the mating behaviour is a main factor affecting individual migration. In a field study, male harrassments induced female emigration at high male density. Simulation, ed away in search of mates at low female density. Simulations of male-female movements based on behavioural data from the field revealed that changes in mate density will induce sex-biased emigration. assessment of migration within a metapopulation in the field during 2 years supported these predictions. Such bias in migration has been reported earlier in other butterfly species with a similar mating system. Consequences of sex-biased emigration on metapopulation dynamics may be spasms in population foundation as these occur only when density 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 between generations may affect metapopulation viability analysis by current models. (C) Elsevier, Paris.