1 Introduction
European countries are spatially dominated by agricultural landscapes
(Kleijn
et al., 2012), yet the ongoing intensification of their management
dramatically reduces biodiversity
(Brooks
et al., 2012; Cardoso et al., 2020). Even though species diversity and
specific ecological traits are well known as key promoters of ecosystem
functioning
(Borer,
Grace, Harpole, MacDougall, & Seabloom, 2017), ubiquitous ecosystem
engineers, such as ants
(Sanders
& van Veen, 2011), are threatened by destruction
(Hendrickx
et al., 2007) and fragmentation of remaining semi-natural habitats
interspersed between arable land
(Ewers
& Didham, 2006). In order to mitigate severe effects on the maintenance
of ecosystem services provided by ants, such as biological pest control
(Östman,
Bengtsson, & Ekborn, 2001; Tscharntke et al., 2012), biodiversity
restoration in modern cultivated landscapes holds great potential
(Tscharntke,
Thies, Kruess, Steffan-Dewenter, & Klein, 2005; Ekroos, Olsson,
Rundlöf, Wätzold, & Smith, 2014). Extensively managed grassland
ecosystems are among the most species-rich habitats in Northern and
Central Europe
(Krauss,
Steffan-Dewenter, & Tscharntke, 2003) and paramount for the diversity
of ants in temperate regions
(Seifert,
2018). These important semi-natural environments are disappearing
rapidly from European agricultural landscapes due to abandonment,
afforestation and conversion to residential areas
(Dengler,
Janišová, Török, & Wellstein, 2014; Valkó et al., 2018). Set-aside land
and other remnants of semi-natural habitats enhance the edge density in
agricultural landscapes, which fosters the diversity and abundance of
ground-dwelling predators like ants
(Haaland,
Naisbit, & Bersier, 2011; Martin et al., 2019) and correspondingly the
success of biological pest control in adjacent farmland
(Gardiner
et al., 2009). However, yield-enhancing ecosystem services rely heavily
on the ability of predator species to disperse into the agricultural
matrix
(Kohler,
Verhulst, Van Klink, & Kleijn, 2008). The enhancement of perennial
non-crop areas through newly established grassland strips, likely
provides refuge habitat not only for common agrobiont species, but also
for more specialized species, if they persist in the long-term
(Dauber
& Wolters, 2005).
Ants are eu-social insects and important consumers of herbivorous
insects, which makes them a key taxon for ecosystem functioning of
temperate grasslands
(Wills
& Landis, 2018). Many ant species can organize mass-recruitment if
sufficient food sources are available
(Seifert,
2018) and this spatial allocation of predatory workers enables ant
colonies to respond effectively to a dynamic and heterogeneous density
of prey in their environment
(Way
& Khoo, 1992). Yet, the importance of ants as consumers and ecosystem
engineers is often underappreciated
(Wills
& Landis, 2018), even though they are the numerically dominant
invertebrates in certain agricultural landscapes.
Offenberg
(2015) showed that the efficiency of ant-mediated biocontrol is
comparable to chemical pesticides, which designates ants as a relevant
target group towards the development of sustainable management practices
of agroecosystems.
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. Along this line, it
is essential to consider that colonies of all ant species in temperate
regions require multiple years to establish, grow and reproduce
(Dauber
& Wolters, 2005; Seifert, 2018). Hence, in an agricultural landscape
long-term set-aside area and permanent grassland interspersion between
arable field crops is required to keep or bring ants back as ecosystem
engineers.
Understanding the ecological function of a species in a particular
habitat requires knowledge of species-specific traits, their dependence
on environmental factors and ecological niches
(Cadotte,
Carscadden, & Mirotchnick, 2011; Gagic et al., 2015). Moreover,
functional traits of ants, such as colony size (number of individuals),
predation on pest insects (proportion of animal based resources in ant
diet) and recruitment behaviour are closely linked to the biological
control services they may provide
(Perović
et al., 2018). Moreover, ant functional traits are linked to
species-specific responses of ants to habitat alteration and management
intensity of agroecosystems
(Ekroos,
Rundlöf, & Smith, 2013).
This study aimed to document the development of ant community
composition and functional diversity within newly established grassland
strips of three years age and adjacent cereal crops. The results were
compared to reference plots in traditionally used old grasslands, and
control plots situated in the surrounding crops. Pest control potential
was quantified in all habitats through predation experiments with
sticky-cards using fruit flies as baits. Further, vegetation cover of
all habitats was recorded, as a high and dense vegetation supports a
higher supply of food resources
(Kruess
& Tscharntke, 2002; Siemann, 1998) and thus might affect the dependency
of predatory arthropods such as ants to feed on experimentally exposed
fruit flies.
At the start, newly established grasslands are assumed to provide
habitats primarily for common agrobiont ant species
(Dauber
& Wolters, 2005) but they may also be colonized by habitat specialists
if they persist in the long term and offer diverse ecological niches.
Further, social insects such as ant colonies have high and continuous
nutrient requirements and should therefore play a key role as biocontrol
agents in agroecosystems. In account of that, the following research
questions were addressed:
1) How do species richness and community composition of ants compare
between newly established grasslands, old grasslands and surrounding
cereal crops?
2) Are newly established grasslands able to develop the functional trait
space covered by ant communities in old grasslands, and further the
prevalence of traits related to biocontrol services?
3) How do the investigated habitat types and vegetation cover affect
provided pest control services, and can predation efficacy be related to
the aboveground activity of ants?