Habitat associations and occupancy patterns of burnet moths (Zygaenidae) in semi-natural pastures in Sweden
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Burnets were surveyed in 100 semi-natural pastures in the province of Ostergotland, southeastern Sweden. We analysed the presence/absence of burnets in relation to habitat characteristics, and species richness of butterflies and plants. Five species were found (Adscita statices, Zygaena osterodensis, Z. viciae, Z. filipendulae and Z. lonicerae), all occurring in 33%-36% of the localities. Among these, four are nationally red-listed. More species were found on (1) large semi-natural pastures, compared with small, (2) low- to medium-grazed semi-natural pastures, compared with heavily grazed, and (3) open semi-natural pastures, compared with wooded. A. statices and Z. viciae had a higher frequency of occupancy at localities surrounded by a large density of pastures, but the occurence of the other species did not rely on this variable. The number of burnet species per locality was positively correlated with the number of butterfly species, and slightly positively correlated with species richness of plants. The difference in species richness among burnets, butterflies and plants may be explained by different responses to grazing pressure; the species richness of burnets and butterflies peaked in localities with a low grazing pressure, while species richness of plants was unaffected by grazing. As burnets are easily surveyed and indicate a high butterfly-species richness, they may be suitable indicators of species richness of pastures. As uniform management with heavy grazing is detrimental for burnets and for many butterflies, it should be avoided at localities with a species-rich fauna.