Direct and indirect effects of land‐use intensification on ant communities in temperate grasslands

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.

Role of grasslands in pest suppressive landscapes: how green are my pastures?

“…2016) and has been shown to be the most harmful management practice on ant species richness and community composition (Heuss et al . 2019). Not surprisingly, plant‐dwelling arthropods, including true bugs and orthopterans, may be more sensitive to mowing than ground‐dwelling arthropods, such as spiders and ground beetles, due to the direct mortality from mowing and the rapid, widespread removal of plant biomass (Torma et al .…”

“…2016), while ant species richness has been observed to increase under sheep grazing (yet decrease under heavy cattle grazing) (Heuss et al . 2019). Mowing has been found to positively influence the abundance and richness of a range of arthropods in roadside grasslands, including ground beetles, weevils, ants and ground‐dwelling spiders (Noordijk et al .…”

“…2010; Heuss et al . 2019). Considering the abundance of grazing pastures in mixed farming regions (Lloyd et al .…”

“…2018; Heuss et al . 2019). Intensively managed grasslands, on the other hand, will almost always see a decline in beneficial arthropods and their resulting services (Kruess & Tscharntke 2002a; Albrecht et al .…”

Ant community composition and functional traits in newly established grasslands within agricultural landscapes

“…Similar to most other grassland taxa, ants are highly responsive to human impact, such as land use change (Dahms et al 2005;Dauber et al 2006). A recent study highlights that ant species richness, as well as functional diversity of ant communities, decreases with increasing land-use intensity in terms of mowing and grazing of grasslands (Heuss, Grevé, Schäfer, Busch, & Feldhaar, 2019). However, to maintain ant biodiversity and their role as biocontrol agents, not only the underlying mechanisms leading to the aforementioned decreases have to be elucidated, but also how habitat restoration, in terms of newly established grasslands, may affect ant communities.…”