Population dynamics and future persistence of the clouded Apollo butterfly in southern Scandinavia: The importance of low intensity grazing and creation of habitat patches

Abstract

We investigated the population dynamics and future persistence of the last remaining Clouded Apollo butterfly metapopulation in southern Scandinavia. Based on three decades of surveys (1984–2015), we modelled colonization-extinction dynamics and local population sizes using habitat patch characteristics and connectivity, while accounting for imperfect detection and uncertainty in the local population sizes. The colonization probability increased with increasing connectivity and the local extinction probability decreased with increasing local population size in accordance with metapopulation theory. The local population size increased with increasing patch area, and was also affected by grazing intensity. Light grazing resulted in larger local populations compared to heavy grazing or no grazing at all. The butterfly population has decreased considerably during the study period and according to projections of future dynamics the estimated extinction risk within the coming 10years is 17%. However, it is possible to change the negative trends and decrease the extinction risk considerably by conservation actions. By optimizing the grazing pressure in existing patches the extinction risk was reduced to 11% (a reduction with 35% compared to the scenario with no conservation action). If a few new patches are created close to the occupied ones the extinction risk can be reduced further. In conclusion, there is a large risk that the Clouded Apollo butterfly will go extinct from southern Scandinavia within the coming decade. However, conservation measures that are focused to the core area of the current distribution and applied soon can considerably improve the situation for the butterfly.