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.

Tudor ‘reform’ treatises and government policy in sixteenth century Ireland

During the sixteenth century hundreds of treatises, position papers and memoranda were composed on the political state of Ireland and how best to ‘reform’, ‘conquer’ or otherwise incorporate that island into the wider Tudor kingdom. These ‘reform’ treatises attempted to identify and analyse the prevailing political, social, cultural and economic problems found in the Irish polity before positing how government policy could be altered to ameliorate these same problems. Written by a broad array of New English, Old English and Gaelic Irish authors, often serving within Irish officialdom, the military, or the Church of Ireland, these papers were generally circulated amongst senior ministers and political figures throughout the Tudor dominions. As such they were written with the express purpose of influencing the direction of government policy for Ireland. Collectively these documents are one of the most significant body of sources, not just for the study of government activity in the second Tudor kingdom, but indeed for the broader history of sixteenth century Ireland. This thesis offers the first systematic study of these texts. It does so by exploring the content of the hundreds of such works and the ‘reform’ treatise as a type of text, while the interrelationship of these documents with government policy in Tudor Ireland, and their effect thereon, is also explored. In so doing it charts the developments from origin to implementation of the principal strategies employed by Tudor Englishmen to enforce English control over the whole of Ireland. Finally, it clearly demonstrates that the ‘reform’ treatises were both central to government activity in sixteenth century Ireland and to the historical developments which occurred in that time and place.

The impact of new public management on the roles of elected councillors, management and the community sector in Irish local government: a case study of Cork County Council

The fundamental aim of this thesis is to examine the effect of New Public Management (NPM) on the traditional roles of elected representatives, management and community activists in Irish local government. This will be achieved through a case study analysis of one local authority, Cork County Council. NPM promises greater democracy in decision-making. Therefore, one can hypothesise that the roles of the three key groupings identified will become more influenced by principles of participatory decision-making. Thus, a number of related questions will be addressed by this work, such as, have the local elected representatives been empowered by NPM? Has a managerial revolution taken place? Has local democracy been enhanced by more effective community participation? It will be seen in chapter 2 that these questions have not been adequately addressed to date in NPM literature. The three groups identified can be regarded as stakeholders although the researcher is cautious in using this term because of its value-laden nature. Essentially, in terms of Cork County Council, stakeholders can be defined as decision-makers and people within the organization and its environment who are interested in or could be affected directly or indirectly by organizational performance. This is an all-embracing definition and includes all citizens, residents, community groups and client organizations. It is in this context that the term 'stakeholder' should be understood when it is occasionally used in this thesis. In this case, the perceptions of elected councilors, management and community representatives with regard to their changing roles are as significant as the changes themselves. The chapter begins with a brief account of the background to this research. This is followed by an explanation of the methodology which is used and then concludes with short statements about the remaining chapters in the thesis.

Interaction strengths and net effects in food web models

Understanding how dynamic ecological communities respond to anthropogenic drivers of change such as habitat loss and fragmentation, climate change and the introduction of alien species requires that there is a theoretical framework able to predict community dynamics. At present there is a lack of empirical data that can be used to inform and test predictive models, which means that much of our knowledge regarding the response of ecological communities to perturbations is obtained from theoretical analyses and simulations. This thesis is composed of two strands of research: an empirical experiment conducted to inform the scaling of intraspecific and interspecific interaction strengths in a three species food chain and a series of theoretical analyses on the changes to equilibrium biomass abundances following press perturbations. The empirical experiment is a consequence of the difficulties faced when parameterising the intraspecific interaction strengths in a Lotka-Volterra model. A modification of the dynamic index is used alongside the original dynamic index to estimate intraspecific interactions and interspecific interaction strengths in a three species food. The theoretical analyses focused on the effect of press perturbations to focal species on the equilibrium biomass densities of all species in the community; these perturbations allow for the quantification of a species total net effect. It was found that there is a strong and consistent positive relationship between a species body size and its total net effect for a set of 97 synthetic food webs and also for the Ythan Estuary and Tuesday Lake food webs (empirically described food webs). It is shown that ecological constraints (due to allometric scaling) on the magnitude of entries in the community matrix cause the patterns observed in the inverse community matrix and thus explain the relationship between a species body mass and its total net effect in a community.