Environmental change and the structure and functioning of invertebrate communities

Land-use change and climate change are considered to be the greatest threats to biodiversity globally. The conversion of natural habitats into agricultural land with remnant patches of the original habitat left embedded within an anthropogenic matrix is one of the main land-use changes. This has been shown to alter species richness and abundance, depending on factors such as remnant area and isolation. Climate change has caused species to shift their distributions, alter their phenologies or risk going extinct. The interaction of habitat fragmentation and climate change exacerbates these problems when the lack of suitable habitat within a species dispersal limits prevents a species from tracking changing climates, forcing its adaptation or extinction. One method attempting to remedy this is to restore habitats in a network across landscapes in order to reduce the isolation between natural communities and increase connectivity across landscape. These areas have been largely assessed using a species-centred approach. In this thesis I investigate these elements of environmental change, and the potential mitigation process of habitat restoration, using a food web and functional approach to assess how these factors affect the structure and functioning of invertebrate communities.
In Chapter 2 I describe the results of a landscape scale study into the effects of habitat fragmentation on sub-tropical rainforest communities in Australia. Using cavity-nesting bees, wasps and their parasitoids as a study community I show that fragmentation effects such as fragment area, isolation and edge effects can impact different trophic levels to different extents, but that this does not necessarily result in a change to the ecosystem function of parasitism.
Using a field-based manipulative experiment, In Chapter 3 I investigate the effects of altered rainfall regimes which may be a consequence of climate change on host-parasitoid food webs and parasitism in a temperate grassland. I show that changes to precipitation regimes disrupts host-parasitoid synchrony between a common grassland leaf-mining insect Stephensia brunichella and its parasitoid Pholetesor arisba. These changes do not cause food web changes at the scale studied, but demonstrate the potential for climate change to alter host-parasitoid synchrony and hence the ecosystem service of parasitism.
Utilising a long-term experiment into the effects of different grazing regimes on the restoration of lowland calcareous grassland in the UK on former arable land, in Chapter 4 I address the impacts of restoration on quantitative food web structure and parasitism. I show that although grazing regime can affect trophic level composition differentially, this does not translate into overall changes in food web structure or parasitism at the field scale studied.
Using the same field experiment, and a novel method for assessing soil ecosystem feeding activity by invertebrates, I investigate the impacts of seasonal grazing regime on soil ecosystem function (Chapter 5). I show that the season of grazing has an impact on the vertical profile of soil ecosystem functioning. I discuss the potential implications of this novel finding for the future of restoration studies and the importance of including below ground processes in ecological studies of environmental change.
This thesis shows that research into the effects of anthropogenically induced environmental change can benefit from a food web and ecosystem functioning approach. However, experimental field studies at larger spatial scales and the inclusion of species traits are needed to fully address these questions.

Advisor: Morris, R
Lewis, O