| Background and Aim
European butterflies are declining, mostly due to habitat loss and fragmentation caused by modern agriculture practices. The large blue butterfly (Phengaris arion) is threatened and does only have a few strongholds left in Sweden. The large blue has a particularly complex lifecycle since the larvae live as parasites on species of the ant family Myrmica. On Gotland, the P. arion population was almost completely extinct after the drought of 2018, but a small increase in individuals has been observed the last years. By assessing habitat requirements of P. arion and compare occupied sites with randomized sites in the landscape the aim of this study is to determine the crucial habitat factors for the survival of P. arion. By assessing these habitat factors we hope to find new methods for conservation of the large blue.
Methods
I will work with a population near Slite on northwestern Gotland, where patch occupancy has been followed since 2017. During the summer of 2021 I will collect data on site occupancy, oviposition behavior of females and habitat mapping in a hectare grid system. Site occupancy will be conducted through a capture-mark-release study. Where adult butterflies are found, grass height, nectar quantity and tree and bush cover will be assessed. Female oviposition preference will be done by following females to determine habitat characteristics around their preferred host plant. As eggs are found, parameters such as plant height and size, phenology of buds and potential Myrmica nests for larvae will be assessed. If ant nests are found, ant individuals will be collected for later species identification. Hectare grid analysis will be performed in both grid cells where the species has been extinct, where they have been found all years since 2017 and where they have never been seen. Nectar quantity, grass height, Myrmica presence and tree and bush cover will be assessed in these hectare grids.
Aims
By doing this research, I aim to determine
(1) Recolonialization success of P. arion after the drought of 2018,
(2) key habitat factors for adult P. arion on Gotland,
(3) population size of P. arion in the study area,
(4) preference and key habitat factors for female egg laying. |