Interactions between seedling herbivory and life history traits affecting restoration of species-rich grasslands

Background/Question/Methods

Species rich upland hay meadows are of high biodiversity importance and are internationally rare.  In recent decades there has been growing interest in restoring botanical diversity of agriculturally improved sites, but little is known about the effects of invertebrate herbivores.  Previous research involving restoration of upland meadows has identified the optimum farm management regime, and the need to add seed of species absent from the seed bank of improved sites which are drivers of above- and below-ground community-level properties, including the hemi-parasite Rhinanthus minor and a variety of early-colonising fungal-facilitating species.  In view of the possible selective pressure slugs exert on seedling recruitment in the field and the lack of knowledge in this context at grassland restoration sites, the acceptability of seedlings of meadow plants to the generalist slug, Deroceras reticulatum were determined in controlled microcosms.  Slugs were offered seedling monocultures and the percentage damage per seedling was recorded at timed intervals over 14 days. 

Results/Conclusions

The results were analysed using a Generalized Additive Mixed Model and showed D. reticulatum to have clear preferences and dislikes for particular species.  Chemical properties of species influenced acceptability, but physical properties were seemingly less effective in seedlings.  The influence of plant hairs (trichomes) was less clear with some hairy species being eaten readily and others virtually rejected, possibly due to a synergistic effect with chemical defences.  Highly acceptable species were Achillea millefolium, several grass species (Holcus lanatus, Festuca rubra, Cynosurus cristatus, Poa trivilais, Agrostis capillaris) and the legume, Trifolium pratense.  The establishment of some of these species, particularly T. pratense, is important during the early stages of meadow restoration as they are associated with promoting soil fungal populations and reducing high residual soil fertility.  Highly unacceptable species, or those suffering very low levels of damage, were characteristic of species-rich meadows (Geranium sylvaticum, Rumex acetosa, Leontodon hispidus, Anthoxanthum odoratum, Sanguisorba officinalis, Ranunculus acris), indicating that they are highly unlikely to be selectively grazed by slugs during the seedling recruitment phase at restoration sites.  In addition, evidence of the selective grazing of R. minor seedlings by slugs and the potential anti-herbivore defensive properties of R. minor will also be presented.  Investigation of the leaf surface of R. minor (seedlings and mature plants) has identified a diverse assemblage of trichomes.  The potential role of trichomes in anti-herbivore defence is an intriguing direction for future research.