This dataset contains data on the distribution and abundance of the Glanville fritillary butterfly (Melitaea cinxia), its host plants Plantago lanceolata and Veronica spicata, and its parasitoid Cotesia melitaearum, in the Åland archipelago in Finland. The study species M. cinxia has been surveyed since 1991 in a metapopulation network of circa 4000 dry meadow habitat patches in a study area of circa 50 by 70 km. The presence of one of its specialist parasitoids C. melitaearum was included in 1993. This dataset covers the years 1993-2017. Data are recorded bi-annually by field assistants. First over a two-week period from late August to early September the patches are visited to search for the presence and abundance of the M. cinxia larval over-wintering nests. Second in the following spring, the occupied patches are revisited to record data on overwinter survival of the larval families and on the potential presence of the parasitoid . Before 2010, data were recorded by hand on paper maps and forms and then entered manually to spreadsheets, and later to a database. The locations and shapes of habitat patches were recorded with GPS devices. From 2010 onwards, the data have been systematically collected and managed with the EarthCape database management system (earthcape.com). Earthcape is used in the field on tablet / laptop computers to find the patches and record data with both GPS and topographic maps. The resulting updated database is then checked for errors, cleaned up and merged with the central database, also maintained with Earthcape. The database is relational in structure in order to handle the different levels of data collection. For more details on how the survey is conducted and data recorded, see Ojanen et al. 2013 This dataset contains data on three nested levels: Patch, Locality visit and Nest. The patch-level file has one row per patch, and the variables describe location and geometry for the (habitat) patch. The Locality visit -file has one row per location*survey combination, and the variables describe patch level habitat quality, host plant abundance and quality, total numbers of M. cinxia nests in the patch classified in several different ways, and total numbers of C. melitaearum in the patch for the particular survey. The nest-level file has one row per M. cinxia over-wintering nest, and the variables describe the location*survey when it was recorded, detailed location information, and host plant and dead/alive status of each nest. Over the 25 years of surveying, the exact variables recorded have varied somewhat according to researcher’s needs and the development of theory around the survey (Ovaskainen & Saastamoinen 2018). Certain core variables have been recorded every year and those have been included in this dataset, but we also include some variables that have not been recorded every year and therefore have missing data for some years. The network of habitat patches is temporally dynamic and thus has also changed shape over the years: new habitat patches of M. cinxia host plants can appear and existing ones can disappear. Patches can also change shape as the host plants spread to new areas or when e.g. construction has removed host plants from other areas. The patch-level geometry variable always gives the most recently recorded geometry of the patch, but when the patch shape has changed, the new geometry has been recorded on the Locality visit level for the year in question. Sometimes separate patches merge into a single patch. In this dataset, patch merging has been performed retroactively to facilitate using the data as a long-term repeated survey. When two patches have merged, the data from those two patches has been retroactively merged in all the previous years, as if they had always been a single patch. References: Ojanen, S., Nieminen, M., Meyke, E., Pöyry, J. & Hanski, I. 2013. Long‐term metapopulation study of the Glanville fritillary butterfly (Melitaea cinxia): survey methods, data management, and long‐term population trends. Ecology and Evolution 3: 3713-3737. Ovaskainen, O. & Saastamoinen, M. 2018. Frontiers in Metapopulation Biology: The Legacy of Ilkka Hanski. Annual Review of Ecology, Evolution, and Systematics 49:231-252.

2019