Migration of the clouded Apollo butterflyParnassius mnemosynein a network of suitable habitats – effects of patch characteristics

Abstract

The clouded ApolloParnassius mnemosyneis a food plant specialist with short but frequent movements between habitat patches. The short average dispersal distances suggest that the probability of colonisation of vacant patches decreases rapidly as the distance between the source and target patches increases, which means that a dense habitat network is needed for the conservation of the species. Both emigration rate and the number of immigrants varied among patches and were not affected only by isolation but also by several other patch characteristics. The model that explained most of the variation in emigration rates among patches included patch area and the number of conspecifics. The area and the population density of the target patch had significant effects on the number of arriving immigrants. Thus, the colonisation of vacant patches is dependent on these patch characteristics. Generally, emigration rates were lower and residence times longer in large patches with many conspecifics. Butterfly density was the most important single factor explaining the variation in the number of immigrants among patches, although the positive effect of the area of the target patch was also significant. As a consequence of the marked positive density dependence caused by conspecific attraction, small patches with higher than average butterfly density, receive more immigrants than could be expected based on the patch area only. Due to conspecific attraction, per capita immigration rates are higher in small than large patches. Thus, immigration may have a more significant effect on the local dynamics of small than large populations.