Current studies on trophic interactions in biodiversity experiments have largely relied on artificially
sown gradients in plant diversity, but removal experiments with their more natural plant community
composition are more realistic. Slugs are a major part of the invertebrate herbivore community, with
some species being common pests in agriculture. We therefore investigated how strongly slugs are
influenced by grassland management, plant biodiversity and composition. Here we analysed the effects
of cutting frequency, fertilizer application and plant functional group composition on slug densities and
their contribution to herbivory on Rumex acetosa in a removal experiment within a >100-year old
grassland in Northern Germany. The experiment was laid out as a Latin rectangle with full factorial
combinations of (i) plant functional group removal (3 levels) using herbicides, (ii) fertilizer application
(2 levels) and (iii) cutting frequency (2 levels). The resulting 12 treatment combinations were replicated
6 times, resulting in 72 plots. We collected a total of 1020 individuals belonging to three species Arion
distinctus (60.4% of individuals), Deroceras reticulatum (34.7%) and Arion lusitanicus (4.9%) using a cover
board technique and additionally measured herbivore damage to R. acetosa. We found the highest slug
abundance on plots with a low cutting frequency and high food resource availability (increased cover of
forbs and taller vegetation). Fertilizer application had no significant effect on slug abundance, but caused
higher herbivore damage to on R. acetosa, possibly as a result of increased tissue quality. The negative
effect of higher cutting frequency on slug abundance was lowest in control plots with their naturally
developed graminoid-forb communities (cutting reduced slug density by 6% in the control vs. 29% in
herbicide plots). Our experiments therefore support the idea that more natural plant species compositions
reduce the impact of disturbances (e.g. through cutting or grazing) on invertebrates.
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