Intensive grazing alters the diversity, composition and structure of plant-pollinator interaction networks in Central European grasslands

Abstract

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.

Livestock density affects species richness and community composition of butterflies: A nationwide study

“…To stop and reverse abandonment, grazing is often seen as an essential tool for nature conservation purposes ( Kapfer, 2019 , Stewart and Pullin, 2008 ). However, whereas intensifying land use of a nearly abandoned pasture might result in positive effects, intensification of an extensively managed pasture might cause declines ( Rakosy et al, 2022 ). Thus, understanding the consequences of different livestock densities is of major importance ( Batáry et al, 2010 ).…”

“…in immature stages. Moreover, high management intensity has been shown to cause negative indirect effects as well, such as a homogenisation of plant communities and a dominance of grasses, resulting in a loss of food plants and nectar sources for insects ( Rakosy et al, 2022 , WallisDeVries et al, 2016 , WallisDeVries and Raemakers, 2001 ). Although we found a linear negative relationship between species richness and herbivore stocking density, negative effects can be expected on the opposite extreme of the gradient as well, i.e.…”

Pollinator‐mediated effects of landscape‐scale land use on grassland plant community composition and ecosystem functioning – seven hypotheses

“…In temperate grasslands, abundant flower‐visiting insects that play an important role in pollination are mainly social and solitary wild bees (Apoidea: Anthophila) and other hymenopterans, hoverflies (Diptera: Syrphidae) and several other dipteran families, several beetle (Coleoptera) families, as well as moths and butterflies (Lepidoptera) (Forup & Memmott, 2005; Michelot‐Antalik et al ., 2021; Rakosy et al ., 2022). In addition, several vertebrate taxa, and in particular nectarivorous birds, are important pollinators in temperate grasslands [e.g.…”

Utilising affordable smartphones and open-source time-lapse photography for monitoring pollinators

“…It is thus critical to monitor plant-pollinator interactions and to understand the factors that cause these interactions to change across space and time. As many species of pollinating insects cannot be identified on sight, most studies quantifying plant-pollinator interactions capture insects that are observed to visit flowers and identifying them later using microscopy (e.g., Motivans Švara et al 2021; Rakosy et al 2022) or DNA barcoding (Creedy et al 2020). While these methods are accurate and can provide museum specimens that are valuable for a wide variety of research purposes (Rakosy et al 2023), they are time consuming, costly to scale, and require expert knowledge in insect taxonomy or barcoding.…”