Mobility and emigration in butterflies

Abstract: Because of its implications for the survival of many species, dispersal plays a key role in conservation biology. A good knowledge about the different factors that influence dispersal decisions is crucial for the understanding of inter-population movements. One factor that can inhibit dispersal is the presence of non-preferred matrix habitat surrounding suitable patches. We found that for Melitaeini butterfly species, which prefer open and sunny habitats, even a small shady area can severely restrain patch emigration. To answer questions about the determinants of dispersal decisions, the main topic in my work has been conspecific density and how it influences patch suitability, movement behaviour, interactions among conspecifics and the evolution of dispersal. By studying within-patch flights in different conspecific densities for both Melitaea cinxia and Melitaea athalia, we found that social interactions, such as males pursuing and courting females, increased with conspecific density. For M. cinxia we also found emigration rates to increase with conspecific density, even in a surplus of resources. This suggests that social interactions can be used by M. cinxia as a cue of conspecific density and thereby indirectly trigger dispersal. To further investigate the generality of our results on the influence of conspecific density on emigration we have analysed the evolution of dispersal in a theoretical model that compared six different situations, differing in the kind of information individuals have about both conspecific density and habitat quality. According to our model, in unpredictable environments, species with no information about habitat quality or conspecific density will employ a highly dispersive strategy, even when dispersal is costly in terms of dispersal mortality. Allowing the organisms to use information about either habitat quality or conspecific density (or both) reduced emigration rates. Further, density-dependent dispersal evolved in all cases of unpredictable environments, provided that individuals had information about conspecific density. Information about both habitat quality and conspecific density will thus have effects on the evolution of dispersal.