Abstract of PhD Thesis

The environmental requirements of Sciomyzidae (Diptera) on turloughs in the west of Ireland with particular reference to the role of Mollusc host / prey communities

Christopher D. Williams, National University of Ireland, Galway (2007)

Turloughs are temporary wetlands unique to the calcarenite bedded limestone in the west of Ireland. As such, many are protected as Special Areas of Conservation (SAC) under the EU habitats directive (1992). A recent review of the literature has revealed that whereas the geology, hydrology and vegetation of turloughs are relatively well known, knowledge of the invertebrate communities is somewhat scanty. The recent work on ground beetles (Carabidae) of Moran (2005) and Regan (2005) has gone someway to redress this. However, only one study to date has considered the dipteran communities of turloughs and only four rather qualitative studies have investigated mollusc communities.

Flies of the family Sciomyzidae have potential as biocontrol agents of snail-borne trematode diseases of man and livestock. They have also been suggested as suitable bio-indicators of habitat quality on wetlands. The aim of the present thesis is to assess the potential of Sciomyzidae and their mollusc host / prey communities as bioindicators of turlough quality. A secondary aim is to take the first steps in quantifying the ecosystem service provided by Sciomyzidae at a turlough under natural conditions.

An intensive study at Skealoghan turlough highlighted the importance of vegetation structure and hydrology for sciomyzid ecology. There was a heavy zonation in fly abundances with neighbouring vegetation zones having quite different faunas. In contrast to studies on carabids at the same site, vegetation structure was the most prominent factor; hydrology occupying an important, but secondary role. A mark-recapture study at Cregaclare turlough gave population estimates of over six flies per square metre and extrapolation of previously reported laboratory studies, indicated that Sciomyzidae could reduce Galba truncatula (Müller) (the host of liverfluke) populations by up to 50%.

Studies of the mollusc communities showed that the mollusc fauna consisted of fully aquatic, temporary wetland specialist and terrestrial wet-grassland species. Sites were more similar to each other later in the season than earlier, but turlough site was a more important grouping variable than time of sampling (though both were statistically significant). Although significantly nested, the mollusc communities showed many site and species idiosyncrasies, which were supported by indicator species analyses and correlations with environmental variables, suggesting that a blanket approach to turlough mollusc conservation is not advisable.

Consideration of Sciomyzidae across a range of sites gave evidence supporting the hypothesis that univoltine species (particularly Ilione albiseta (Scopoli) and Pherbina coryleti (Scopoli)) dominate on temporary wetlands. Analyses gave evidence that species richness and total abundance of Sciomyzidae displayed a unimodal peak at intermediate soil moistures across the full hydrological regime.  Total abundance of Sciomyzidae, however, was highest when vegetation structure was maximal across a range of turloughs in one vegetation zone (Carex nigra zone). However, despite a general preference for long vegetation, smaller species (e.g. Pherbellia nana) prefer shorter swords indicating that a diverse range of management regimes within sites would maximise β diversity and a range of management regimes between sites would maximise γ diversity. A Generalised Linear Model (GLM) Poisson regression of I. albiseta abundance, on the Carex nigra dataset, indicated a negative coefficient for total prey abundance (when other factors were controlled for) highlighting a predation pressure by this species. These results were supported by a classical square-root transformed regression of I. albiseta abundances for the Carex nigra dataset. Finally, the simulation tool was applied to study the auto–ignition behavior of hydrogen in our RCM.