Understanding the interactions between grasses and herbivores is central to the conservation of species-rich grasslands and the protection of our most important crops against pests. This talk will show how and why silica is an effective anti-herbivore defence in grasses, its potential impact on herbivore populations and how silica could be useful in sustainable methods of crop protection in future.

Herbivorous waterfowl move seasonally between aquatic and terrestrial feeding areas, but the factor(s) regulating these switches are poorly understood. We use optimal foraging models to show that seasonal changes in metabolic foraging cost, but not food quantity or quality, determine a mute swan habitat shift between riparian pasture and river. Few studies currently consider such inter-habitat differences in foraging costs.

Using long-term data for red deer and vegetation in Rum, we identify climatic windows explaining most phenological variation in deer demography and vegetation productivity. Our results suggest that most weather effects on deer condition are felt indirectly through variation in plant growth. Nevertheless, the upward trend observed in plant productivity, is not matched by an increase in the deer population. 

Pea aphid facultative symbionts are known to have striking effects on their hosts including changes in colour and protection from natural enemies or heat shocks. In a field experiment, we have found that aphids with or without the symbiont Hamiltonella defensa differ in their effects on plant quality with consequences for the community of other herbivores naturally-colonizing our experimental plots.

The impact of livestock grazing on grass tussock carbon stocks and grass root decomposition was studied in a landscape-scale upland grazing experiment. High sheep densities reduced tussock number and thereby vegetation carbon stocks, but grazing had little effect on root decomposition. The long-term consequences for soil carbon have been modelled.

It has been suggested that natural enemies such as pararasitoid wasps can benefit plant fitness by reducing herbivore damage. However, thus far, evidence supporting this position is scarce. Here in lab and semi-field experiments, we compare seed production and viability in a trithophic system involving a solitary and a gregarious parasitoid and their shared host.

It has been suggested that negative effects of climate change on forest health could be mitigated by planting trees of non-local provenance that are adapted to predicted future climates. We investigate the importance of tree provenance for associated organisms using a model system of gall-forming herbivores (Hymenoptera: Cynipidae) on Sessile oak (Quercus petraea), at an experimental plantation in northwest France.

Although seedling selection by herbivores is linked to constitutive chemical defences, it remains unclear whether herbivores detect these defences prior to attack despite the presumably pressing need to signal defensive capability before tissue is damaged. We show here that olfactory selection of seedling material by snails is strongly related to gustatory acceptability and plant age.