Abstract
Land‐use intensification is a major driver of local species extinction and homogenization. Temperate grasslands, managed at low intensities over centuries harbored a high species diversity, which is increasingly threatened by the management intensification over the last decades. This includes key taxa like ants. However, the underlying mechanisms leading to a decrease in ant abundance and species richness as well as changes in functional community composition are not well understood. We sampled ants on 110 grassland plots in three regions in Germany. The sampled grasslands are used as meadows or pastures, being mown, grazed or fertilized at different intensities. We analyzed the effect of the different aspects of land use on ant species richness, functional trait spaces, and community composition by using a multimodel inference approach and structural equation models. Overall, we found 31 ant species belonging to 8 genera, mostly open habitat specialists. Ant species richness, functional trait space of communities, and abundance of nests decreased with increasing land‐use intensity. The land‐use practice most harmful to ants was mowing, followed by heavy grazing by cattle. Fertilization did not strongly affect ant species richness. Grazing by sheep increased the ant species richness. The effect of mowing differed between species and was strongly negative for Formica species while Myrmica and common Lasius species were less affected. Rare species occurred mainly in plots managed at low intensity. Our results show that mowing less often or later in the season would retain a higher ant species richness—similarly to most other grassland taxa. The transformation from (sheep) pastures to intensively managed meadows and especially mowing directly affects ants via the destruction of nests and indirectly via loss of grassland heterogeneity (reduced plant species richness) and increased soil moisture by shading of fast‐growing plant species.
Highlights
In temperate Europe, grasslands have been extensively managed over centuries by grazing and low‐intensity mowing
They differ in their effects on biodiversity in grasslands (Simons et al, 2014; Socher et al, 2012), and effects change along the management intensity gradient
We test whether the ant community composition changes along a land‐use intensity gradient and investigate which morphological and life history functional traits are reduced in communities when certain species disappear
Summary
In temperate Europe, grasslands have been extensively managed over centuries by grazing and low‐intensity mowing. Fertilization and mowing are often highly correlated (Blüthgen et al, 2012), and high intensities of both result in the homogenous vegetation structures and reduced plant diversity (Harpole & Tilman, 2007) This leads to overall multitrophic homogenization (Gossner et al, 2016) and a decline in arthropod species richness and abundance (Haddad et al, 2009). Grazing effects are to date not sufficiently studied in temperate grasslands with long grazing history (Pihlgren et al, 2010) It is poorly understood whether grazing affects ants directly due to the destruction of nesting sites by trampling of livestock or indirectly, through increased structural heterogeneity due to selectively removed plant biomass, localized fertilization by feces deposition, altered plant species richness, and reduced plant cover, which increases ground temperature (Boomsma & Van Loon, 1982). We test whether the ant community composition changes along a land‐use intensity gradient and investigate which morphological and life history functional traits are reduced in communities when certain species disappear
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