Increasing patch area, proximity of human settlement and larval food plants positively affect the occurrence and local population size of the habitat specialist butterfly Polyommatus coridon (Lepidoptera: Lycaenidae) in fragmented calcareous grasslands

Abstract

Abstract. Which factors influence the occurrence, population size and density of species in fragmented habitat patches are key questions in population and conservation ecology. Metapopulation theory predicts that larger and less isolated habitat patches should positively influence species occurrence and population size. However, recent studies have shown that habitat quality, human activity and permeability of the landscape surrounding habitat patches may be also important. In this paper we test the relative effects of habitat patch characteristics, human settlement and landscape permeability on the occurrence, local population size and density of the Chalk-hill Blue Polyommatus coridon a charismatic butterfly inhabiting calcareous grasslands in a fragmented landscape in southern Poland. Patch occupancy rate (corrected for the butterfly detection probability) was 0.45. Habitat patch area, proximity of human settlement and cover of larval food plants positively affected occurrence of the Chalk-hill Blue. Local population size of the Chalk-hill Blue was positively affected by patch area and proximity of human settlement, and negatively by patch isolation. Local density was higher in patches located close to human settlement. Our study is one of the few showing a positive effect of human settlement on a grassland specialist butterfly although the mechanism hidden behind this phenomenon is unknown and requires further examination. In order to maintain local populations of the Chalk-hill Blue in southern Poland, conservation action should be focused on large, closely connected calcareous grasslands. Moreover, extensive management of this habitat should be maintained by local inhabitants who are better placed to undertake such work.

Biology and biogeography of the chalk-hill blue Polyommatus coridon – insect of the year 2015 for Germany, Austria and Switzerland

“…These results on population genetics are mostly supported by a classical ecological study from the Göttingen region which demonstrated that the population density of P. coridon is mainly dependent on the quantity of its larval host plant, in this case H. comosa, but not on the effect of habitat isolation and habitat quality (Krauss et al 2005). Quite similar results were obtained by Rosin et al (2011) southwest of Kraków (southern Poland); they showed that the best predictors for a potential habitat being occupied or not are its size and the percentage cover by the host plant, in this case S. varia. Hence, the chalk-hill blue is mostly dependent on the preservation of large habitats.…”

Factors affecting road mortality and the suitability of road verges for butterflies

“…Human settlement also increased the number of species on verges. In farmland areas, human settlements often have small gardens with numerous flowers that can provide a supplementary resource for butterflies (Rosin et al, 2011) and this may explain the positive effects of human settlements on species richness found in our study. However, the mechanism leading to the increased proportion of roadkills is difficult to extrapolate.…”

How life history affects threat status: Requirements of two Onobrychis-feeding lycaenid butterflies, Polyommatus damon and Polyommatus thersites, in the Czech Republic

“…The results must be viewed with reservations, however, because only four of the 54 sites surveyed were occupied by P. damon, rendering any inference rather spurious. Still, we found that both butterflies required sites with high host plant density, quite expectably in monophagous species (e.g., Krauss et al 2004;Rosin et al 2011;Roy & Thomas 2003), and both tended to occur at sites with variable management. P. thersites, but not P. damon, also increased with proportional representation of grazing, in accordance with our oviposition patterns observations.…”

“…The fate of particular species depends on a combination of species-specific habitat requirements, supply of potential habitats (area, connectivity) in a given region, and habitat quality, which can be manipulated by management of remnant habitat patches (Krauss et al 2005;Rosin et al 2011;Thomas et al 2001). Because management actions appropriate for one species may directly harm others (Bourn & Thomas 2002;Dolek & Geyer 2002), diversified land management offers the only chance to secure diverse arrays of specialised species both within insular reserves and in surrounding landscapes Morris 2000;Oliver et al 2010).…”