Åland Islands

In the Åland Islands in SW Finland, the research is focused on the Glanville fritillary (Melitaea cinxia), its parasitoid wasps and larval host plants. The main Åland Island contains thousands of habitat patches (dry meadows) where at least one of the two larval host plant species, Plantago lanceolata and Veronica spicata, occur, and which are considered to be potentially suitable for the Glanville fritillary.

Each autumn, all known habitat patches are surveyed for the presence of larval groups of the Glanville fritillary and the powdery mildew Podosphaera plantaginis, as well as scored for several habitat patch attributes. The latter include information on the occurrence of the host plants, landscape structure and habitat quality. In the following spring, all patches occupied in the previous autumn are re-visited, and the numbers of larval groups, numbers of larvae and numbers of cocoons of the local specialist parasitoid wasp Cotesia melitaearum are counted. This large-scale monitoring work has accumulated a comprehensive and unique database on the occurrence of the Glanville fritillary and on the habitat patch characteristics. Moreover, all the habitat patches have been positioned with an accurate GPS-machine, which allows analyses of the spatial patterns and properties of the patch network with GIS.

Based on this monitoring work, we know the locations of the vast majority of the suitable habitat patches in Åland, including about 4111 dry meadows. The habitat patches are distributed across the Åland’s land area of 1480 km2, but most of them occur in clusters, typically of tens of patches. The main reason for the aggregated distribution of habitat patches is that the meadows mainly occur within the cultural landscape on rocky outcrops, typically near small villages. The patch-aggregates form well over one hundred habitat patch networks, many of which are occupied by the Glanville fritillary, and where the respective metapopulations have relatively independent dynamics. In 2005, about 769 patches were occupied by the Glanville fritillary.

Occupied (filled) and empty (open) habitat patches suitable for the Glanville fritillary in the Åland Islands in the autumn 2005.