The effects of invertebrates on the plant communities in upland hay meadows

Abstract

Species rich upland hay meadows are of high biodiversity importance and are internationally rare. There is increasing interest in restoring botanically diverse meadows in the uplands but little is known about the role of invertebrates. The purpose of the project was to investigate the role of (i) slugs as seedling herbivores and (ii) pollinators in affecting the plant communities. Research has revealed important interactions between invertebrates and plant life history traits with implications for grassland restoration. Slugs are known to affect plant communities by the selective seedling removal of more acceptable species, although few studies have considered their impact at restoration sites. A glasshouse feeding trial showed the acceptability of seedlings of different meadow plants to slugs is influenced by plant defensive properties. Field investigations of slug population densities identified a negative correlation with increasing levels of agricultural improvement. This relationship was partly driven by the increase in grass abundance cover in agriculturally improved meadows and may be influenced by the anti-feedant properties of silica-rich grass leaves. A 3-year mesocosm study found evidence that slugs are an important selective force affecting seedling recruitment and community composition. The selective seedling removal of the hemi-parasite and keystone species Rhinanthus minor was a key finding of this study. Use of Scanning Electron Microscopy showed the leaf surface of R. minor to be characterised by a diverse assemblage of trichomes which may play an important role in anti-herbivore defence. Parallel declines in pollinator and insect-pollinated plant populations have raised concerns that smaller populations of important pollinator groups such as bumblebees may be reducing seed set by plants. Survey work showed upland hay meadows to be an important forage resource for common and rare/scarce bumblebees. Bumblebees visited a small number of forage plants, most notably R. minor, Trifolium species and Geranium sylvaticum. Pollen supplementation tests did not find significant evidence that reproductive output of R. minor and G. sylvaticum (a gynodioecious species) was limited by pollination services. Testing of a new system to record pollinator visitors to flowers proved highly effective and offers the potential to significantly reduce time and labour input into the study of plant-invertebrate interactions. The project has shown that invertebrates are an important functional group affecting the success of plant species in hay meadows. The findings provide new and important information to the industry in developing management prescriptions for restoring upland hay meadows and other botanically rich plant communities.