When habitat management can be a bad thing: effects of habitat quality, isolation and climate on a declining grassland butterfly

The conservation of most temperate grassland habitats and their characteristic fauna and flora requires regular low-intensive forms of land-use to counteract natural succession. Although many species tolerate moderate disturbance regimes, some are known to be susceptible to grazing or mowing, thereby causing a management dilemma. One of these species is the Woodland Ringlet butterfly, Erebia medusa. In this study, we analysed which environmental factors determine the occurrence of E. medusa in the Diemel Valley (Central Germany). Furthermore, we conducted microclimatic measurements during the winter months to investigate the role of the litter layer as a microclimatic buffer. Patch occupancy in the Diemel Valley was well explained by the amount of litter present in a patch and connectivity to other inhabited patches. The role of local climatic conditions could not be clarified, due to inter-correlations with connectivity. During the winter, the air temperature inside the litter layer was significantly less variable than above it. We conclude that the current distribution of E. medusa in the Diemel Valley is caused by the combined effect of habitat quality and connectivity, and perhaps also by climatic factors. The importance of the litter layer reflects the dependence of E. medusa on low-intensive or absent land-use. In addition, the litter layer possibly constitutes an essential habitat element, as it buffers temperature fluctuations and thus probably reduces the energy consumption of overwintering larvae. Given the species' preference for abandoned grasslands, the conservation of E. medusa requires a low-intensity habitat management, for example, by rotational grazing or mowing of small parts of the sites. On the landscape level, the preservation of well-connected habitat networks is important.