The importance of interaction strength for food web dynamics and ecosystem functioning

Global biodiversity is eroding at an alarming rate, through a combination of anthropogenic disturbance and environmental change. Ecological communities are bewildering in their complexity. Experimental ecologists strive to understand the mechanisms that drive the stability and structure of these complex communities in a bid to inform nature conservation and management. Two fields of research have had high profile success at developing theories related to these stabilising structures and testing them through controlled experimentation. Biodiversity-ecosystem functioning (BEF) research has explored the likely consequences of biodiversity loss on the functioning of natural systems and the provision of important ecosystem services. Empirical tests of BEF theory often consist of simplified laboratory and field experiments, carried out on subsets of ecological communities. Such experiments often overlook key information relating to patterns of interactions, important relationships, and fundamental ecosystem properties. The study of multi-species predator-prey interactions has also contributed much to our understanding of how complex systems are structured, particularly through the importance of indirect effects and predator suppression of prey populations. A growing number of studies describe these complex interactions in detailed food webs, which encompass all the interactions in a community. This has led to recent calls for an integration of BEF research with the comprehensive study of food web properties and patterns, to help elucidate the mechanisms that allow complex communities to persist in nature. This thesis adopts such an approach, through experimentation at Lough Hyne marine reserve, in southwest Ireland. Complex communities were allowed to develop naturally in exclusion cages, with only the diversity of top trophic levels controlled. Species removals were carried out and the resulting changes to predator-prey interactions, ecosystem functioning, food web properties, and stability were studied in detail. The findings of these experiments contribute greatly to our understanding of the stability and structure of complex natural communities.

The use of different blood sample preparations in the development of biomarkers for the environmental monitoring of domestic farm animals

The application of biological effect monitoring for the detection of environmental chemical exposure in domestic animals is still in its infancy. This study investigated blood sample preparations in vitro for their use in biological effect monitoring. When peripheral blood mononuclear cells (PBMCs), isolated following the collection of multiple blood samples from sheep in the field, were cryopreserved and subsequently cultured for 24 hours a reduction in cell viability (<80%) was attributed to delays in the processing following collection. Alternative blood sample preparations using rat and sheep blood demonstrated that 3 to 5 hour incubations can be undertaken without significant alterations in the viability of the lymphocytes; however, a substantial reduction in viability was observed after 24 hours in frozen blood. Detectable levels of early and late apoptosis as well as increased levels of ROS were detectable in frozen sheep blood samples. The addition of ascorbic acid partly reversed this effect and reduced the loss in cell viability. The response of the rat and sheep blood sample preparations to genotoxic compounds ex vivo showed that EMS caused comparable dose-dependent genotoxic effects in all sample preparations (fresh and frozen) as detected by the Comet assay. In contrast, the effects of CdCl2 were dependent on the duration of exposure as well as the sample preparation. The analysis of leukocyte subsets in frozen sheep blood showed no alterations in the percentages of T and B lymphocytes but led to a major decrease in the percentage of granulocytes compared to those in the fresh samples. The percentages of IFN-γ and IL-4 but not IL-6 positive cells were comparable between fresh and frozen sheep blood after 4 hour stimulation with phorbol 12-myrisate 13-acetate and ionomycin (PMA+I). These results show that frozen blood gives comparable responses to fresh blood samples in the toxicological and immune assays used.