Abstract (eng)
The flower-butterfly networks of different land use types of grassland in the "National Park Neusiedler See - Seewinkel'' were analysed. The land use types were (1) pastures with mainly Przewalski’s horses grazing there, (2) pastures grazed by ranging non-stationary cattle and (3) meadows maintained without large grazing animals. Data sampling took place in June and July 2021 during a drought period. Overall, 4160 flower-butterfly interactions involving 27 butterfly and 59 plant species, were observed. Besides the description of the overall network structure, network metrics such as specialisation H2 and vulnerability were calculated. At species level, specialisation d’ and species strength were computed for the most often visited plants and butterflies, respectively. Additionally, 15 years of observation data was used to compare the relative abundance of butterfly species with their observed frequency in flower-butterfly interactions. Network specialisation H2 did not correlate with flower supply and varied also not systematically between land use types but was influenced by the interaction of land use type and observation month. Vulnerability decreased with lower land use intensity. Species diversity of plants and butterflies involved in networks was highest on meadows. At all three land use types diversity of interacting species decreased from early to high summer due to drought. No plant or butterfly species in the more detailed analyses showed a high specialisation or strength. Floral colour, nectar amount, and inflorescence type had a significant impact on visitation rate, whereas UV patterns did not have an effect. Overall, butterflies preferred yellow flowers, a high nectar amount, and racemes and composite inflorescences over single flowers. Although the more detailed analysed species Polyommatus icarus, Plebejus argus, Coenonympha pamphilus and Melanargia galathea were opportunistic regarding their flower visits, preferences in colour, corolla tube length and nectar amount were observed. Contrary to the overall trend, M. galathea preferred violet blossoms with a low nectar reward. Coenonympha pamphlilus and Plebejus argus tended to visit plants with corollas under 5 mm, whereas Polyommatus icarus and Melanargia galathea preferred corolla tubes longer than 10 mm.