268 research outputs found
Crab Burrowing Limits Surface Litter Accumulation in a Temperate Salt Marsh: Implications for Ecosystem Functioning and Connectivity
No full textBurial of aboveground plant litter by animals reduces the amount available for surface transport and places it into a different environment, affecting decomposition rates and fluxes of organic matter to adjacent ecosystems. Here we show that in a Southwestern Atlantic salt marsh the burrowing crab Neohelice granulata buries aboveground plant litter at rates (0.5–8 g m−2 day−1) comparable to those of litter production (3 g m−2 day−1). Buried litter has a low probability (0.6%) of returning to the marsh surface. The formation of burrow excavation mounds on the marsh surface is responsible for most litter burial, whereas litter trapped in burrows was an order of magnitude lower than rates of burial under excavation mounds. Crab exclusion markedly increased surface litter accumulation (3.5-fold in just 21 days). Tides with the potential to transport significant amounts of surface litter are infrequent; hence, most litter is buried before it can be transported elsewhere or decomposes on the surface. Crab litter burial can account for the observed low levels of surface litter accumulation in this ecosystem and likely drives organic matter transformation and export. The impacts of ecosystem engineering by this crab species are therefore substantial and comparable in magnitude to the large effects found for tropical crabs and other litter-burying organisms, such as anecic earthworms.Fil: Gutierrez, Jorge Luis Ceferino. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales; Argentina. Cary Institute of Ecosystem Studies; Estados Unidos. Grupo de Investigación y Educación en Temas Ambientales (GrIETA) - Estación Biológica Las Brusquitas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Jones, Clive G.. Cary Institute of Ecosystem Studies; Estados UnidosFil: Ribeiro, Pablo Damián. Grupo de Investigación y Educación en Temas Ambientales (GrIETA) - Estación Biológica Las Brusquitas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencia Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; ArgentinaFil: Findlay, Stuart E. G.. Cary Institute of Ecosystem Studies; Estados UnidosFil: Groffman, Peter M.. Cary Institute of Ecosystem Studies; Estados Unidos. City University of New York; Estados Unido
On the osmotic signal and osmosensing mechanism of an ABC transport system
No full textWat verandert er in het zenuwstelsel als een dier iets leert? Hoe worden herinneringen opgeslagen in de hersenen? Hieraan ten grondslag ligt het vermogen
van het zenuwstelsel om zich aan wisselende omstandigheden aan te passen, of, met andere woorden, plastisch te zijn. Zoals elk orgaan zijn onze hersenen opgebouwd uit afzonderlijke cellen, de hersencellen ofwel neuronen. De werking van de hersenen berust op de communicatie tussen de neuronen. De communicatie vindt
plaats op plaatsen waar de membranen van neuronen heel dicht bij elkaar liggen, de zogenaamde synapsen...
Zie: Chapter 8
Estimating the Demand for Union-Led Learning in Scotland
No full textThis research paper was commissioned and funded by the Scottish Trade Union Congress (STUC). It is being disseminated through the TUC’s unionlearn High Road project. The project is part of a community programme called Equal – a European Social Fund initiative that tests and promotes new means of combating all forms of discrimination and inequality in the labour market. The GB Equal Support Unit is managed by ECOTEC. Unionlearn is the TUC organisation that supports union-led strategies on learning and skills. It helps unions open up learning and skills opportunities for their members and to develop trade union education for their representatives and officers.
‘The art of salvation is but the art of memory’ : soul-agency, remembrance and expression in Donne and Shakespeare
No full textThis thesis examines how the dislocation of old beliefs in post-Reformation England affected perceptions of the soul in the work of Donne and Shakespeare. The introduction, using Augustinian discourses on the tri-partite soul, explores how the soul is imagined in post-Reformation England. Current debates on interiority, the climate of anxiety that surrounds religious upheaval, historical readings of the composition of the soul and the problems of its actual representation on the page and stage are discussed. The patterning of Augustine‟s tri-partite model of Reason, Will and Memory is examined, and the regenerative power of concordant Memory that can bind together a harmonic trinity is offered as a solution to the fractured soul. The first part of the thesis concentrates on writings that represent Donne‟s anxieties over the fate of the soul as he contemplates conversion from Catholicism to the new religious order. Chapter One is an enquiry into his unpublished works from 1601 to 1611 and examines the idea of the wandering soul, from The Progresse of the Soule, to the Divine Poems and finally to the redeemed soul seen in the form of Elizabeth Drury in the Anniversaries. In this chapter, I argue that Donne is searching for an alternative Marian aesthetic as he leaves behind his Catholic past, a new image of divine intercession for the Protestant world that might offer him comfort and a route to salvation. Chapter Two explores his very public sermons after he enters the ministry until his death. Here, a pattern of redemption is argued through the salvic properties of the living Word of the sermon that is relayed through the performative power of the preacher. The preacher‟s working space and the power of the Word to viscerally transform the congregation are central here to the soul‟s salvation. The second part examines how Shakespeare explores the „journey‟ of the soul through a selection of his plays, but where the limits of genre impose restrictions on Shakespeare‟s development of an image of redemption. Chapter Three examines the wandering soul in The Merchant of Venice and Othello. Through the trope of marriage, the fate of the souls of Jessica and Othello are explored as they find themselves marginalized in an inhospitable Venice, while their pasts have been forgotten in the attempt to convert to Christianity. Chapter Four explores the use of the female character as an image of Memory that can generate hope, reading Juliet in Romeo and Juliet and Cordelia in King Lear as “soul agents”, whose beneficence can bring about redemptive change. However, the thesis argues that the genre of tragedy examined here limits the soul agent. Chapter Five argues for an alternative genre that opens up the possibilities for the successful portrayal of the soul agent. In the romance plays, the representation of the soul can be seen working successfully to a redemptive conclusion. Romance dramas foreground their slippages in plot and take us into dreamscapes at the centre of which is an essential female influence. Marina in Pericles, Perdita in The Winter‟s Tale, Innogen in Cymbeline and Ariel/Miranda in The Tempest provide a link with Donne‟s presentation of the soul as female in the Anniversaries. Both Donne and Shakespeare suggest the idea of the female in literature as a redemptive figure, away from earlier discourses on the soul that finds itself at the mercy of epistemological wrangling. Donne and Shakespeare re-instate that sacredness and place it within art as an image of Memory, a vital component of Augustine‟s tri-partite soul, but also as an active and vibrant image of possibilit
Impacts of signal crayfish on stream fishes
No full textInvasive species cause biodiversity and economic loss globally. Invasive crayfish have a wide range of effects as a result of their high densities and biomass, feeding at multiple trophic levels, aggressive competition for shelter and ecosystem engineering. In Britain, the invasive signal crayfish Pacifastacus leniusculus has displaced the native white-clawed crayfish Austropotamobius pallipes from much of its former range and occupied previously crayfishfree
habitats. Signal crayfish could affect fish populations by preying upon eggs, juvenile and adult fish and competing for food and shelter. This thesis assesses the extent to which signal crayfish can affect densities of the commercially important brown trout Salmo trutta, and a species of benthic fish of conservation concern, the European bullhead Cottus gobio, in upland streams. This thesis also investigates the extent to which signal crayfish predation could affect salmonid egg survival
through a combination of controlled field and laboratory experiments. Electric fishing was used to estimate fish densities from tributaries of the upper River Tees, north east England. Model selection was then used to determine which factors most affected bullhead and 0+ (less than one year old) brown trout densities. Signal crayfish density
was negatively related to both bullhead density and the density of 0+ brown trout. Substrate composition and flow variables and were also selected as predictors of 0+ brown trout and bullhead densities. Small (10-16.2 mm carapace length (CL)) crayfish and fine material apparently reduced buried sea trout S. trutta egg survival in controlled field experiments. However, in laboratory studies, only larger crayfish were found to significantly reduce the survival of salmon S. salar eggs, and this reduction only affected eggs on the surface of the gravel and not buried eggs. These results suggest that signal crayfish pose a threat to both salmonid and bullhead populations, and that, where possible, the sites chosen for reintroduction or habitat
enhancement for salmonids and sculpins should be free of invasive crayfish. Evidence for signal crayfish predation upon buried salmonid eggs remains equivocal, although this study provides definite evidence that large signal crayfish will prey upon exposed Atlantic salmon eggs. Both egg predation, and other mechanisms by which signal crayfish may affect salmonid and bullhead populations, are worthy of further investigation. Structural equation models should be used to further investigate relationships between the densities of a range of fish and crayfish species
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Inviscid mean flow through and around groups of bodies
No full textGeneral estimates are derived for mean velocities through and around groups or arrays of fixed and moving bodies, in unbounded and bounded domains, which lie within a defined perimeter. Robust kinematic flow concepts are introduced, namely the Eulerian spatial mean velocity u−E in the fluid volume between the bodies, the Eulerian flow outside the group, \bmu(0)E, and the Lagrangian mean velocity of material surfaces or fluid particles as they pass through the group of bodies (u−(S)L, u−(P)L). The Eulerian mean velocity is related to the momentum in the fluid domain, and is mainly influenced by fast moving regions of the flow. The Lagrangian mean velocity weights slowly moving regions of flow and is related to how material sheets deform as they are advected through groups of bodies. When the bodies are well-separated, the interstitial Eulerian and Lagrangian mean velocities (u−(I)E, u−(I)L), are defined and calculated in terms of the far-field contributions from the velocity or displacement field within the group of bodies.
In unbounded flow past well-separated bodies situated within a rectangular perimeter, the difference between the Eulerian and Lagrangian mean velocity is negligible (as the void fraction of the bodies, α→0). Within wide and short rectangular arrays, the Eulerian mean velocity is faster than the free-stream velocity U because most of the incident flow passes through the array and u−E=U(1−α)−1. Within long and thin rectangular arrays (and other cases where the reflux velocity is negligible), the Eulerian mean velocity, u−E=U(1−(1+Cm)α)/(1−α), is slower than the free-stream velocity, because most of the incident flow passes around the array. For a spherical or circular arrays of bodies, the particle Lagrangian mean velocity is u−(P)L=U(1+Cmα)−1 and differs from u−E. These calculations are extended to examine the mean and interstitial flow through clouds of bodies in bounded channel flows.
The new concepts are applied to calculate the mean flow and pressure between and outside clouds of bodies, the average velocity of bubbly flows as a function of void fraction, and the tendency of clouds of bubbles to be distorted depending on their shape
Effects of Microtopography on Hydrology, Physicochemistry, and Vegetation in a Tidal Swamp of the Hudson River
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