Summer drought shapes grassland butterfly-flower networks more than management type in an Austrian conservation area

Summer drought shapes grassland butterfly-flower networks more than management type in an Austrian conservation area. Flower-butterfly net- works on three grassland types in the National Park Neusiedler See – Seewinkel were analysed, viz. (1) a fenced pasture grazed mainly by Przewalski’s horses at low densities, (2) pastures grazed by non-stationary cattle and (3) meadows maintained by mowing. Sampling took place in June and July 2021 during a drought period. We observed 4,160 flower-butterfly interactions involving 27 butterfly and 59 plant species, including 147 interaction pairs not previously recorded. Species diversity and composition of interacting communities varied across the three grassland types and two survey months, with highest diversities on mown meadows. Nectar flower abundance did not differ between grassland types, but decreased from early to high summer. Network specialization H2’ and modularity Q did not vary systematically between grassland types, but decreased in response to drought. All observed flower-visiting butterfly species visit multiple nectar plant species, but average species-level specialization d’ was higher on meadows than on pastures and further decreased with summer drought. This suggests that partitioning of nectar sources among butterflies is more effective at times of high supply, while overlap in resource use increases during drought. These results suggest that grassland butterflies in the study area respond opportunistically to shortages in nectar flower abundance caused by summer drought, whereas extensive management by grazing vs. mowing left a rather minor signature on these ecological networks. Due to their higher nectar flower abundance mown meadows are important for maintaining butterfly diversity in this large conservation area.