The coprophagous guild

Coprophages are animals that utilise dung as a food resource, and are easily manipulated in experiments designed to investigate the relationships between species and guilds, with ecosystem processes. This allows scientists to make predictions concerning the effect of habitat management and community structure on ecosystem functions and services. Changes in assemblage characteristics through human impacts such as habitat disturbance, management, or natural processes such as grazing, may have important consequences for the ecosystem services provided by biodiversity (Loreau et al., 2001). Interspecific variation in resources processing, intraspecific interactions, and impacts on the physical environment are potential mechanisms by which species richness may affect functional processes (Larsen et al., 2005). Herbivores such as deer are able to indirectly influence processes such as nutrient cycling and decomposition through their quantitative and qualitative control of resource inputs such as dung (Harrison and Bardgett, 2003a). Deer produce large quantities of dung which attracts a diverse range of coprophagous invertebrates, the most conspicuous of which are dung beetles in the genera Geoptrupidae and Scarabaeidae (Stewart, 2001). In the Letterewe oak woodland extensive pitfall trapping revealed that while diverse, the

coprophagous Coleoptera fauna was most conspicuously represented by one species Geotrupes stercorosus. Dung feeding beetles are highly sensitive to changes in dung resources (Nichols et al., 2008) and anthropogenic disturbance (Scheffler, 2005). In the UK, two nationally scarce species are specifically associated with deer dung, certain Staphylinidae prey on invertebrates found in dung, and a distinct dipteran fauna also utilise this resource. In many woodlands, deer are the primary or sole source of dung, and the widespread use of avermectins to control intestinal parasites of grazing livestock mean that deer dung may provide refugia for coprophagous invertebrates on which these chemicals have a detrimental impact (Stewart, 2001). Invertebrates found in association with dung provide an important component of the diet of predatory vertebrates at crucial times of the year. Dor beetles (Geotrupid and Typhoues spp.) accounted for more than 50% of prey items in the winter diet of tawny owls Strix aluco due to a temporal scarcity of small rodents in the New Forest, Hampshire, while Aphodius spp. have been found to comprise an important alternative food source for the threatened greater horseshoe bat Rhinolophus ferrumequinum between July and October, a period when females are under severe physiological stress as lactation progresses, (Stewart, 2001). Dor beetles are also utilised by this species during periods of emergence from winter hibernation, while several other species of bats are also thought to make use of insects associated with dung.

5.1.1.1 The ecology of dung removal

Through manipulation of faeces during the feeding process, removal of dung can provide valuable ecosystem services such as biological pest control, soil fertilization, bioturbation, plant growth enhancement, secondary seed dispersal and parasite control, as well as playing a more limited role in pollination and trophic regulation (Shepherd and Chapman, 1998;

Andresen, 2003; Nichols et al., 2008). The excreta voided by vertebrates contains a substantial proportion of the nutrients that were consumed, and the redistribution of these throughout the plant growth cycle is an important limiting factor on primary production. The removal of waste below the soil surface by dung beetles allows micro-organismal and chemical breakdown of the nutrient rich material, making resources available to plants (Nichols et al., 2008). Tunnelling species of dung beetle displace and mix sediment particles contributing to bioturbation that can influence soil-dwelling organisms and plant productivity by increasing soil aeration and water porosity (Nichols et al., 2008). There is much evidence reporting significant yield increases as a result of dung beetle facilitated nutrient mobilisation of dung in agricultural systems, although there is a lack of evidence in natural, particularly

tropical forest conditions (Nichols et al., 2008). Other influences include parasite suppression, for example by reducing the abundance of helminth eggs that pass through the gut of the beetle, parasite dispersal through the action of transporting dung-borne pathogens either internally or externally, and control of flies through direct competition for dung resources, mechanical destruction of dipterous eggs, and predation of flies by mites phoretic on dung beetles (Nichols et al., 2008). Lastly, some dung beetles are unique in having roles in trophic regulation, through predation of leaf cutter ant queens of the genus Atta, a principle herbivore in the Neotropics, and although rare, some species have obligate pollinator roles for decay-scented flowers (Nichols et al., 2008).

5.2 Aims

The hypothesis that the ecosystem modifying processes brought about by deer grazing may alter habitat conditions such as vegetation architecture and species diversity, which in turn affect the availability of resources to invertebrates, such that different invertebrate guilds will respond to deer exclusion in distinctive and possibly contrasting ways, was tested. The aim was to examine these effects on functional traits of the hoverfly, epigeal arthropod, and parasitoid assemblage of the Letterewe oak woodland, which will provide a useful tool with which to examine the impact of grazing management on biodiversity. The aims of this chapter are:

• To assess the role of fencing to exclude grazing as a red deer management practise in impacting functional responses of invertebrate diversity in the Letterewe oak woodland.

• To determine the factors affecting the variation in guild responses in the Letterewe oak woodland.

• To quantify the contribution of geotrupid dung beetles, and the influence of grazing exclosures on the removal of red deer dung pellet groups, and discuss the potential consequences for ecosystem functional processes.

• To make recommendations for planning and management of the Letterewe oak woodland to maintain guild composition.

The hypotheses that guild structure does not vary between grazed and un-grazed woodland plots, and shows no association with habitat variables, and that there is no effect of geotrupid beetles, or grazing treatment, on removal rates of experimental dung pellet groups were tested. By identifying the primary components that determine guild composition and function

in the Letterewe oak woodland, it will be possible more effectively to assess the consequences of management practises and grazing policy for biodiversity in red deer habitats.

5.3 Methods

Epigeal invertebrates, syrphids and parasitoids were sampled using both pitfall traps and malaise traps, in grazed and un-grazed exclosure plots ranging in age from one to fifteen years, in the Letterewe oak woodland in 2007 and 2008. Details of the study site, general sampling methods and habitat survey methods can be found in Chapter Two.