Rapid selection for increased dispersal rates by the endangered butterfly Phengaris (Maculinea) arion across restored landscapes

Abstract When designing restorations for durable metapopulations of endangered butterflies, it is important to understand how frequently the adults mix between sites and their probability of colonising vacant patches unassisted by human translocations. We analysed 43 examples of natural dispersal by Phengaris arion L. to restored sites in three regions following its reintroduction after extinction to the UK. We compared the years taken to reach restored habitats with the distance from a source colony, the number and density of P. arion on source sites, the size of source sites, the nature of the intervening matrix, summer temperatures, the incidence of drought and whether a more dispersive phenotype has evolved across restored landscapes. Isolation of sites was the most important constraint on the colonisation of new habitats, followed by the number, but not the density, of P. arion on source sites. Emigration was more frequent in warm summers and when the habitat was degraded by drought, but neither factor remained significant in multifactorial analyses. A matrix of woodland between sites was a greater barrier to dispersal than open or mixed terrain, but again insignificant in multifactorial analyses. A more mobile phenotype of P. arion has evolved while it exploited vacant habitat patches during its first 10–12 generations in the UK. Adults now fly twice as far to find new colonies as in the early years. We map the probabilities of linking restored sites with neighbouring populations in three former landscapes in the Cotswold Hills of Gloucestershire, UK.