Abandonment of traditional land use and climate change threaten the survival of an endangered relict butterfly species

Abstract

The decline of butterflies exceeds those of many other animal taxa due to their high sensitivity to habitat alterations driven by land‐use change. Moreover, cold‐adapted species frequently suffer severe range retractions due to rising temperatures at their trailing‐edge range margins. In this study, we aim to identify drivers of occupancy of the post‐glacial relict species Lycaena helle at three spatial scales – (i) landscape, (ii) habitat, and (iii) microhabitat – in one of its last refuges in central Europe. In our study in the Eifel low mountain range (western Germany), the occurrence of L. helle was mainly driven by the (i) isolation, (ii) size, and (iii) quality of habitat patches. Lycaena helle formed metapopulations that were dependent on networks of interconnected but often small habitat patches. Habitat quality within the semi‐natural grasslands was determined by (i) macro‐ and mesoclimate, (ii) host‐plant abundance, and (iii) vegetation structure, which was interrelated with microclimate. Lycaena helle preferred moist, nutrient‐poor grasslands in deep, narrow valleys at the highest elevations of the study area, which were characterised by (i) cold winters, (ii) high abundance of the host plant, and (iii) short and sparse swards providing a warm microclimate in summer. According to these findings, abandonment of traditional land use and climate change are considered the most severe threats for long‐term survival of the species. Hence, conservation measures should aim at maintaining and restoring networks of large and well‐connected habitat patches of high quality, preferably in cold‐air depressions within mountain systems.

Occurrence of an endangered grassland butterfly is mainly driven by habitat heterogeneity, food availability, and microclimate

“…To determine patch occupancy of E. aurinia , each grassland patch was sampled at least once during the peak of the flight period between late May and early June from 9:00 a.m. to 17:00 p.m. under favorable weather conditions (>18°C, sunny weather, hardly windy; Scherer et al ., 2021). Per patch, the occurrence of adults was recorded by walking in loops with a distance of 50 m between each loop.…”

“…To cover all habitat structures, especially of small patches, we varied the starting point of each following survey accordingly. A patch was classified as occupied if at least three adults (as an indicator for an indigenous population) or a larval web was detected (Anthes et al ., 2003b; Scherer et al ., 2021).…”

Rejuvenation and restoration measures foster specialised and threatened carabid beetle species in montane heathland ecosystems

“…Vegetation height was measured with a folding rule at five randomly selected spots within each plot and then averaged. The duration of sunshine in June was recorded using a horizontoscope (Scherer et al, 2021). Data on mean annual temperature were derived from 1‐km 2 grid datasets of Germany's National Meteorological Service (personal communication), which contain 10‐year (2010–2019) mean values.…”

Limestone quarries are the most important refuge for a formerly widespread grassland butterfly

“…The size of the patches varied between 0.2 and 15.8 ha (mean: 2.6 AE 0.3 ha). Connectivity of the patches was measured as the geometric mean of the next three populated patches (Eichel & Fartmann, 2008;Scherer et al, 2021). Edge-to-edge distances from the focal patch to the three other patches were computed using the proximity-analysis tool 'near table' in ArcGIS 10.2.…”

“…Host-plant availability and microclimatic conditions are the most important predictors of butterfly habitat quality (García-Barros & Fartmann, 2009;Curtis et al, 2015). The microclimate within a butterfly habitat is mainly influenced by vegetation structure (García-Barros & Fartmann, 2009;Scherer et al, 2021), which usually depends on land use (Dover & Settele, 2009). Most thermophilous habitatspecialist butterflies require warm microhabitats for oviposition (e.g.…”