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.