Aoife Delaney (@Ifa_Dee)
Supervisor: Jane Stout
Title: Do principals of cross congruence apply in a naturally disturbed habitat?
Cross congruence is a measure of the degree to which diversity (number or composition of species) of different taxa follow broadly similar patterns in response to environmental conditions. In situations where cross congruence is strong, measuring the diversity of a single taxon can provide information regarding overall diversity, and this has led to the development of indicator taxa. Indicator taxa may be used to indicate general patterns of biological diversity or environmental conditions, often with the inference that where the environmental conditions are favourable for one taxon, other target taxa will benefit. The use of indicator taxa has obvious economic appeal, but cross congruence has been shown to vary greatly in different studies. Habitat heterogeneity and environmental stress can reduce the correlation of diversity among different taxonomic groups.
Within the EU, states which have signed up to the Habitats Directive (Council Directive 92/43/EEC) monitor the condition of habitats of conservation concern (Annex I habitats) using standard methods and report their results to the European Commission. Indicator species are used as part of this habitat assessment. Dune slacks, an EU Annex I habitat, are temporary ponds in sand dunes which can persist for long periods, many having been formed as part of the initial dune-building phase. Despite being stable physical features, they experience both environmental stress (annual flooding and desiccation) and temporal habitat heterogeneity, and this raises questions: do principals of cross-congruence apply here, and are indicator species effective? This study compared patterns of diversity among three different taxonomic groups, to test whether cross congruence was observed. Communities of plants, snails and water beetles in twenty-four dune slacks in Ireland were compared using diversity indices and ordination techniques. Dune slacks were assessed on the basis of the indicator species used in reporting to the European Commission, and the biological assemblages of sites which passed and failed the assessment were compared. The results of this research will help to evaluate current monitoring techniques which are in use throughout the EU and guide monitoring approaches for dune slacks in Ireland.
Qiang Yang (Marvin) (@ )
Supervisor: Ian Donahue & Andrew Jackson
Title: Stronger perturbations increase the complexity of ecological stability
The stability of ecosystems determines the sustainability of the biological resource and services that nature offers us, and an understanding of mechanisms and drivers of ecological stability has vast implications for the sustainability and management of natural resources as well as the protection and restoration of ecosystems. Much effort has been contributed to understanding the factor that determines the stability of biological communities. A challenging aspect of stability is its many components, including asymptotic stability, resilience, resistance, robustness, persistence, variability and so on, but most of the previous research failed to analyse ecological stability from an comprehensive angle and we know remarkably little about the mechanisms underpinning relationships among components of stability. Therefore, focus on single stability elements may cause an underestimate of the “real stability” of ecosystems. Here in our research, by simulating the dynamics of 13 four-species food webs following perturbations varying in strength, we show that stronger perturbations decouple the relationship between stability components, i.e. that the efficacy of the single stability element in representing the general character of ecological stability becomes lower under strong perturbations. It is therefore necessary to investigate ecosystem stability from multiple angles, especially under strong disturbance frequently shown in real nature. The decoupling effect of perturbations on the multidimensionality of ecological stability is universal across most of the 14 food-web motifs in our research, implying a similar pattern in more complex large ecological networks.
Alewynne McGeever (@)
Supervisor: Fraser Mitchell
Title: Population dynamics of Pinus and Ulmus in Europe during the Holocene.
This work investigates and compares the population dynamics of Pinus and Ulmus in Europe, during the Holocene, at varying temporal and spatial scales, by using recently developed and novel modelling methods. The first component characterises the European-wide post glacial rise and mid-Holocene decline experienced by both genera. Pollen data was extracted from 330 sites on the European Pollen Database (EPD). The depth of rise and decline events for each genus in each site core was defined by applying a spline curve, to remove stochastic noise from the pollen data, and identifying the range of depths along which the pollen values increased or decreased.
The R package Bchron was used to calibrate radiocarbon dates and produce an age-depth model for each site, using stochastic linear interpolation and Monte Carlo methods. The age-depth model data was applied to the event depth range to produce a probability distribution of when the rise and decline events occurred.
The second component characterises Ulmus and Pinus when they were abundant on the European landscape. Depth and magnitude data of maximum pollen values for both genera were gathered from the EPD. The age-depth models were used to determine the age of the maximum pollen value depths.
These data were then plotted on maps and empirical Bayesian kriging was used to interpolate the spatial and temporal dynamics of these population events in the two tree genera. This work, therefore, presents novel techniques to quantifying tree population dynamics, and also provides insight into the specific dynamics of two major tree genera in Europe.
Supervisor: John Parnell & Trevor Hodkinson
Title: Phylogenetics of Camellia (Theaceae) in Indochinese Peninsula
Tea, camellias and oil camellias from the genus Camellia L. (Theaceae) are commercially highly important. About one third of all known Camellia species occur in the Indochinese Peninsula, of which half are endemic. Many new names of Camellia are still being described from this area, which may suggest that it was previously under-collected. Almost no work, however, has focused on the phylogenetics of Camellia in this area. This project aims to address these issues using morphological and molecular approaches. Morphological studies, consisting of a comparison and description of various macro-characters of specimens and palynological analyses, will be undertaken to clarify the boundaries of species in this notoriously variable genus. DNA markers derived from nuclear and chloroplast genomes will be selected to generate molecular sequence data, which will be used to reconstruct a robust phylogenetic tree. A new classification of this genus could then be proposed based on both morphological and molecular data. Species that have potential to supply new traits to the cultivars of tea, camellias and oil camellias could also be identified.
Conor Owens (@ )
Supervisor: Fraser Mitchell & Jane Stout
Title: Biodiversity in willow evapotranspiration systems for wastewater treatment
Constructed wetlands are increasingly seen in Ireland and abroad as a solution to the on-site treatment of wastewater from domestic and other sources in rural areas. They are likely permanent features in our landscape that will proliferate into the future. Willow evapotranspiration systems are a subtype suitable for application in areas with low permeability subsoils. These systems are often promoted as having a beneficial role with respect to biodiversity but this has not been rigorously evaluated. This project aims to assess the plant and invertebrate biodiversity of these systems and the contribution they make to the biodiversity of the wider landscape. The factors driving biodiversity in these systems are being investigated and thus this project will provide management recommendations to maximise this biodiversity. This project involves cross discipline collaboration, drawing on expertise from both the TCD School of Natural Sciences and the TCD School of Engineering.