4.1 Species richness and functional diversity
The results of this study demonstrate the potential of newly-established grasslands to promote ant species richness in agricultural landscapes, but only if preserved over long periods of time. Cumulated ant species richness was comparable between old and new grasslands, and significantly higher compared to surrounding cereal crops. However, even though ant species richness and abundance had already increased to high levels after three years of establishment, the new grasslands had not yet assembled ant communities of the same complexity as seen in old grassland.
Species loss or nestedness accounted for almost 50% of the variation in species composition among the habitat types, indicating that new grasslands and cereal crops habitats comprise a poor selection out of the species pool present in old grasslands. These results were supported by ordination analysis, showing that the ant community composition of new grassland transects was mostly shaped by ubiquitous agrobiont species, such as L. niger and a few Myrmica species, which are known to be resistant to anthropogenic disturbance and also inhabit cereal crops (Seifert, 2018). After three years, new grasslands were still in earlier stages of ant community succession (Dauber & Wolters, 2005), and lacked habitat specialists such as L. fuliginosus, L. alienus agg. and S. cunicularia . Colonies of these species require a constant supply of food resources and take several years to establish, grow and reproduce (Dauber & Wolters, 2005; Seifert, 2018).
The time lag in the colonisation of newly established grasslands by ants was also reflected by the results for the functional trait space, biocontrol experiments and biocontrol related traits in new grasslands. Principal component analysis showed that the functional richness of new grasslands was determined by three common agrobiont species (L. niger, S. rufibarbis, M. rugulosa ), which were also present within cereal crops habitats. However, this fraction out of the local species community already provided three functional traits essential for biocontrol services, namely a predatory diet, the ability of workers to organize mass recruitment and large colony sizes. Interestingly, the extension of the functional trait space covered by ants in old grasslands was determined solely by the species L. fuliginosus , which is highly distinctive for many traits among the Central European ant fauna. These ants obligately nest inside tree stems, maintain massive trail systems, attain by far the largest colony sizes of all encountered species, and, as a socially parasitic species, they depend on other ants as hosts for colony foundation.
These findings suggest that accumulating woody elements and allowing more advanced stages of vegetation succession (Dahms, Lenoir, Lindborg, Wolters, & Dauber, 2010) will help to promote functional richness and biocontrol related traits of ant assemblages in new grasslands, and thus to prevent the loss of biodiversity and associated ecosystem services in agricultural landscapes. In account of the high biocontrol potential of species such as L. fuliginosus , new grasslands would thereby not only extend the range of suitable foraging and nesting sites for ants (Armbrecht, Perfecto, & Vandermeer, 2004), but further increase the contribution that ants (and other common predators such as carabids and spiders) in such habitats may provide to agroecosystem functioning in their surroundings.