Complex socio-economic, political and demographic factors have driven the increased conversion of Europe’s semi-natural grasslands to intensive pastures. This trend is particularly strong in some of the most biodiverse regions of the continent, such as Central and Eastern Europe. Intensive grazing is known to decrease species diversity and alter the composition of plant and insect communities. Comparatively little is known, however, about how intensive grazing influences plant functional traits related to pollination and the structure of plant-pollinator interactions. In traditional hay meadows and intensive pastures in Central Europe, we contrasted the taxonomic and functional group diversity and composition, the structure of plant-pollinator interactions and the roles of individual species in networks. We found mostly lower taxonomic and functional diversity of plants and insects in intensive pastures, as well as strong compositional differences among the two grassland management types. Intensive pastures were dominated by a single plant with a specialized flower structure that is only accessible to a few pollinator groups. As a result, intensive pastures have lower diversity and specificity of interactions, higher amount of resource overlap, more uniform interaction strength and lower network modularity. These findings stand in contrast to studies in which plants with more generalized flower traits dominated pastures. Our results thus highlight the importance of the functional traits of dominant species in mediating the consequences of intensive pasture management on plant-pollinator networks. These findings could further contribute to strategies aimed at mitigating the impact of intensive grazing on plant and pollinator communities.

Sampling took place during peak flowering in the middle of June 2018. We chose this point in time because it represents the period when most flowering plants are in bloom, and in the case of the hay meadows it reflects the maximum development of the vegetation before mowing (see also [38]). Within each of the five sites, we established 10 transects (with the exception of one pasture for which we could only place 6 transects), each measuring 30x2m. Transects were placed with a minimum distance of 30m between them, and towards the nearest field margins. In each transect, we visually estimated the percent cover of flowers/inflorescences of each plant species (i.e. [40]). We used the standardized transect walks to also quantify pollinator species and plant-pollinator interactions. One collector walked each transect for an active sampling period of 15 min. We thereby sampled over 3 days in total (for 300 min in pastures and 450 min in hay meadows), with two days in which a pasture and a hay meadow site were sampled in parallel, and a day in which the remaining hay meadow was sampled.

All Hymenoptera, Diptera and Lepidoptera that contacted the reproductive structures of the flowers were treated as potential pollinators and collected using sweeping nets (we hereafter refer to these groups as pollinators for simplicity); easily identifiable species were identified on site and released, while all other individuals were collected and frozen for further processing. All plant species were identified to species level. Among pollinators, 85.5% of all individuals were identified to species level and 99.5% to genus level (see species lists in S2 Table, S3 Table).

Sampling location: Opawskie Mountains, at the border between Poland and the Czech Republic (for co-ordinates see datatable).

Samling period: middle of June 2018. 

Sampling method: Within each of the five sites, we established 10 transects (with the exception of one pasture for which we could only place 6 transects), each measuring 30x2m. Transects were placed with a minimum distance of 30m between them, and towards the nearest field margins. In each transect, we visually estimated the percent cover of flowers/inflorescences of each plant species. We used the standardized transect walks to also quantify pollinator species and plant-pollinator interactions. One collector walked each transect for an active sampling period of 15 min. We thereby sampled over 3 days in total (for 300 min in pastures and 450 min in hay meadows), with two days in which a pasture and a hay meadow site were sampled in parallel, and a day in which the remaining hay meadow was sampled.

All Hymenoptera, Diptera and Lepidoptera that contacted the reproductive structures of the flowers were treated as potential pollinators and collected using sweeping nets (we hereafter refer to these groups as pollinators for simplicity); easily identifiable species were identified on site and released, while all other individuals were collected and frozen for further processing. All plant species were identified to species level. Among pollinators, 85.5% of all individuals were identified to species level and 99.5% to genus level."