Mobility, habitat selection and population connectivity of Lycaena helle in central Sweden : implications for conservation

Abstract: Lycaena helle is an endangered butterfly that is mainly threatened by habitat degradation and fragmentation. For all species with a fragmented distribution, knowledge about mobility, habitat requirements and connectivity is key to developing successful conservation strategies. This study was conducted close to Östersund, in central Sweden, and aimed to investigate the mobility of L. helle, identify remote-sensed predictors of L. helle occurrence, examine the relationship between L. helle density, the abundance of its host plant and vegetation height and to classify local populations according to their importance for the connectivity on a regional level. A mark-recapture study was performed, which found that L. helle is extremely sedentary, faithful to its habitat and appears to be reliant on females for long-distance dispersal. The recorded flight distances were in most cases longer than what has been found in Central Europe. A resource selection function was used to identify important predictors of L. helle occurrence among five variables computed from remote-sensed data; vegetation height, variation in vegetation, solar radiation, slope and aspect. Solar radiation and slope can be recommended for inclusion in future models. Probability of occurrence of L. helle increased at higher solar radiation, as L. helle is dependent on high insolation. helle. Slope had a negative effect and is hypothesized to act as a proxy for wetness, as L. helle is strongly linked to wetland habitats and as low-gradient areas gather water whereas steep areas shed water. Host plant abundance and vegetation height were inventoried and tested for correlations with L. helle density. There was a significant but weak positive correlation between the abundance of the host plant and the density of L. helle. The weak correlation implies that L. helle is either primarily limited by something else than its host plant or that it can only use the host plant when it grows under certain conditions. L. helle density was negatively correlated with vegetation height, likely caused by the late succession stage of most habitat patches in the study area, which induces selection for lower vegetation heights. The connectivity analysis identified so-called stepping stones, i.e. populations that are particularly important from a connectivity perspective and to which conservation efforts should be directed. Retained or improved connectivity is stressed as fundamental for the conservation of the species. Dispersal corridors improve connectivity and are suitable as habitat patches in themselves, meaning that they merit conservation efforts. The timing and frequency of the maintenance of dispersal corridors is crucial and there is a need for better communication with the parties responsible. To improve the long-term viability of the studied metapopulation, it is recommended to make a dispersal corridor to suitable habitats in Tysjöarna nature reserve to increase the extent of the metapopulation. With the onset of climate change, retained connectivity is yet more important since large networks of populations are more viable and have a higher adaptability to new environmental conditions.