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See detailAn agent-based micro-simulation framework to assess the impact of river floods on transportation systems: implementation trajectory for an assessment in the Brussels metropolitan area
Saadi, Ismaïl ULg; Eftekhar, Hamed ULg; Mustafa, Ahmed et al

in International Journal for Traffic and Transport Engineering (IJTTE) Belgrade 2014 Proceedings (2015)

Several studies were made to assess the direct damage but few studies tackled the topic related to the assessment of indirect damage. This paper discusses the development of a large scale agent-based ... [more ▼]

Several studies were made to assess the direct damage but few studies tackled the topic related to the assessment of indirect damage. This paper discusses the development of a large scale agent-based micro-simulation framework to assess the economic damage caused by river floods. The advantage of this approach is that the economic loss can be assessed at individual level. For that purpose, relationship is established between costs and trips cancelation/duration growth. As the numerical simulations depend largely on the initial demand, the accuracy of the data is fundamental. The model is based upon several disaggregated data related to mobility behaviour of the Belgian citizens. The study area covers the Brussels metropolitan area which was subjected to several floods in the past and may see the risk increasing in the coming decades. [less ▲]

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See detailVoyage(s) à travers le thymus
Geenen, Vincent ULg

Book published by Presses ULg (2015)

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See detailGiven to a Deity? Religious and Social Reappraisal of Human Consecrations in the Hellenistic and Roman East
Caneva, Stefano ULg; Delli Pizzi, Aurian ULg

in Classical Quarterly (2015)

Various cases of human beings ‘dedicated’ to deities are attested in Greek epigraphic evidence. Are these kinds of offerings comparable to the dedication of inanimate objects? Besides, does the fact that ... [more ▼]

Various cases of human beings ‘dedicated’ to deities are attested in Greek epigraphic evidence. Are these kinds of offerings comparable to the dedication of inanimate objects? Besides, does the fact that someone is said to be ‘sacred’ to a specific deity necessarily involve that he went through a process of dedication? This article aims at providing a global picture of different situations in which processes of dedications took place. Among the several issues that are tackled, the cornerstone of this article consists of two questions: for what purposes did some people decide to consecrate a human being to a deity and what were the consequences for the consecrated individuals on religious and social levels? Different categories of persons will be contrasted, in terms of processes through which they acquire their new status but also in terms of the freedom/lack of freedom which is conveyed by this new status. It will also be shown that, as far as method is concerned, it is necessary to complete a lexical analysis with a contextual perspective for a deeper understanding of the problem. [less ▲]

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See detailAn original solver for spillway flow
Goffin, Louis ULg; Erpicum, Sébastien ULg; Dewals, Benjamin ULg et al

Poster (2015)

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See detailQuantitative temperature monitoring of a heat tracing experiment using cross-borehole ERT
Hermans, Thomas ULg; Wildemeersch, Samuel ULg; Jamin, Pierre ULg et al

in Geothermics (2015), 53

The growing demand for renewable energy leads to an increase in the development of geothermal energy projects and heat has become a common tracer in hydrology and hydrogeology. Designing geothermal ... [more ▼]

The growing demand for renewable energy leads to an increase in the development of geothermal energy projects and heat has become a common tracer in hydrology and hydrogeology. Designing geothermal systems requires a multidisciplinary approach including geological and hydrogeological aspects. In this context, electrical resistivity tomography (ERT) can bring relevant, qualitative and quantitative information on the temperature distribution in operating shallow geothermal systems or during heat tracing experiments. We followed a heat tracing experiment in an alluvial aquifer using cross-borehole time-lapse ERT. Heated water was injected in a well while water of the aquifer was extracted at another well. An ERT section was set up across the main flow direction. The results of ERT were transformed into temperature using calibrated petrophysical relationships. These ERT-derived temperatures were then compared to direct temperature measurements in control piezometers collected with distributed temperature sensing (DTS) and groundwater temperature loggers. Spatially, it enabled to map the horizontal and vertical extent of the heated water plume, as well as the zones where maximum temperatures occurred. Quantitatively, the temperatures and breakthrough curves estimated from ERT were in good agreement with the ones observed directly during the rise and maximum of the curve. An overestimation, likely related to 3D effects, was observed for the tail of the heat breakthrough curve. The error made on temperature can be estimated to be between 10 to 20 %, which is a fair value for indirect measurements. From our data, we estimated a quantification threshold for temperature variation of 1.2°C. These results suggest that ERT should be considered when designing heat tracing experiments or geothermal systems. It could help also to assess the geometrical complexity of the concerned reservoirs. It also appears that ERT could be a useful tool to monitor and control geothermal systems once they are in operation. [less ▲]

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See detailUsing zero-inlated models to predict the relative distribution and abundance of roe deer over very large spatial scales
Bouyer, Yaëlle ULg; Rigot, Thibaud; Panzacchi, Manuela et al

in Annales Zoologici Fennici (2015), 52

In Norway, recovering populations of large carnivores commonly prey on roe deer (Capreolus capreolus). Understanding predator habitat use and ecology requires fine-scaled information on prey distribution ... [more ▼]

In Norway, recovering populations of large carnivores commonly prey on roe deer (Capreolus capreolus). Understanding predator habitat use and ecology requires fine-scaled information on prey distribution and abundance. However, the massive spatial scales at which large carnivores use the landscape presents many practical and statistical challenges for developing functional prey distribution models. Pellet-count data from >1000 km of transects gathered across southeastern Norway from 2005 to 2011 were used to derive a map of relative prey abundance for roe deer. These data were modeled using zero-inflated hurdle models using both environmental and anthropogenic variables. Snow depth and agricultural fields were the most significant variables in explaining both presence and abundance. Internal k-cross validation of the model showed medium accuracy (Spearman r = 0.35), whereas external evaluation carried out on the basis of independently collected snow-tracking data (Spearman r = 0.37) and hunting statistics (Spearman r = 0.88) showed high accuracy. The map generated can facilitate both the study of broad scale processes linking predators and prey as well as roe deer management in southeastern Norway. [less ▲]

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See detailToward a Consistent Application of International Financial Reporting Standards (IFRSs) across Companies and Countries
Yammine, Mira ULg

Doctoral thesis (2014)

International Financial Reporting Standards (IFRSs) were developed to be a single set of high-quality globally accepted accounting standards. They are meant to allow uniformity in financial reporting ... [more ▼]

International Financial Reporting Standards (IFRSs) were developed to be a single set of high-quality globally accepted accounting standards. They are meant to allow uniformity in financial reporting, enhance comparability of financial statements in the midst of economical globalization, and allow companies with international subsidiaries to prepare their financial statements using similar global standards. The objective of the dissertation is to study whether the application of IFRSs is consistent across companies and countries; in particular we tackle the following two questions: -Does the application of IFRSs in the preparation of financial statements lead to consistency? -Does the public enforcement of accounting standards impact the consistent application of IFRSs? To answer the first question we have addressed standard IAS 36 that was developed by the International Accounting Standards Board (IASB) and covering impairment of assets. We found that managers’ opportunism still has an impact on the impairment of assets recognition and magnitude when taking impairment decisions. To address the second question, a survey covering enforcement of accounting standards activities was prepared and sent to public enforcement bodies in a number of countries mandating the adoption of IFRSs. The survey allowed us to construct an index that represents the activities of the public enforcement bodies. We studied the impact of public enforcement on specific applications of the standards, the results show a decrease in earnings management in countries with effective public enforcement. [less ▲]

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See detailGathering and Handling of Granular Materials under Microgravity Conditions
Opsomer, Eric ULg

Doctoral thesis (2014)

When a granular material is driven in microgravity environment, one can assist to the formation of dense and slow regions in the system. Indeed, given the dissipative character of the collisions in the ... [more ▼]

When a granular material is driven in microgravity environment, one can assist to the formation of dense and slow regions in the system. Indeed, given the dissipative character of the collisions in the media, energy is lost at each particle interaction and the grains begin to clump locally. The phenomenon has been observed for the first time in the late nineties during sounding rocket experimentation by Falcon and his coworkers and has attracted the interest of many scientists since then. However, precise laws describing the formation and the dynamics of such clusters are still lacking. In order to allow an intensive study of the phenomenon, the European Space Agency set up the SpaceGrains project. Small bronze spheres are enclosed in a rectangular cell and vertically driven by to pistons oscillating in phase opposition. Our work consists in the preparation of the SpaceGrains experiment via molecular dynamics simulations and the elaboration of models predicting the behaviour of the system. Before we started our study concerning SpaceGrains, we reproduced and extended Falcon’s sounding rocket experiments. We showed that, in addition to the granular gas and the cluster, another dynamical regime can be observed in the system. Indeed, for higher filling fractions, the entire granular media behaves like one single completely dissipative particle called the bouncing aggregate. Bouncing modes are observed and can be explained considering the bouncing ball paradigm. Moreover, we highlighted the role of the packing fraction φ as well as the size of the particles R on the different observed dynamics. Within the frame of the SpaceGrains device, we studied the impact of all tunable parameters of the experiment on the dynamics of the system. Thanks to an appropriate scaling all transition points that we obtained by varying the driving amplitude A, the packing fraction and the dimen- sions of the cell L fall along a same theoretical curve. The latter is explained regarding the energy transfer from the piston towards the center of the cell. Once the clustering was controlled, we investigated the handling of the agglomerate. By compartmentalizing the container, local trapping can be achieved and a granular pendant of Maxwell’s demon can be observed in microgravity. Based on the measured particle flux between the compartments, we realized a theoretical model predicting the asymptotic steady state of the system depending on the total number N of particles. In a clustered system, we investigated the impact of asymmetrical driving on the system’s dy- namics. We showed that the mean position of the cluster can be fully controlled via the amplitude ratio a. Moreover, the natural fluctuations of the agglomerate around its equilibrium position are dictated by the driving frequency f and the mass of the cluster. Finally, we realized simulations of driven bi-disperse gases and investigated the segregation phenomena in the system. We showed that clustering and segregation are strongly linked and that the size and the mass of the particles impact the segregation dynamics in different ways. [less ▲]

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See detailEtude et Modélisation de la contribution des macrophytes flottants (Lemna minor) dans le fonctionnement des lagunes naturellles
Tangou Tabou, Thierry ULg

Doctoral thesis (2014)

Waste stabilization ponds (WSP) are widely used in the treatment of domestic and industrial wastewaters in industrialized countries and in developing countries including the Democratic Republic of Congo ... [more ▼]

Waste stabilization ponds (WSP) are widely used in the treatment of domestic and industrial wastewaters in industrialized countries and in developing countries including the Democratic Republic of Congo. Several organisms (e.g., bacteria, algae, protozoa, and aquatic plants) are involved in the treatment process occurring in the WSP. Therefore, the performance of such systems strongly depends upon the management of the existing macrophytes (or at least the management of the most dominant species). Indeed, large biomass coverage of floating macrophytes can induce several dysfunctions within the ponds (e.g., second pollution due to the death and the settling of the macrophytes, difficulties in harvesting valuable biomass for animal feeding or pharmaceutical purposes, etc.) and can threaten the surrounding ecosystems (i.e., fauna and flora) through the releases of partially or unpurified waters. This study aimed at investigating the contribution of floating macrophytes, namely that of duckweed (Lemna minor), which are the most common species, in the functioning of natural WSP. Specifically, the objectives were: (i) the modeling of the growth kinetics of Lemna minor based on the key environmental influencing factors (nutrients concentrations, light intensity, pH, temperature); (ii) the characterizations of the stoichiometry of the growth of Lemna minor and the gas/liquid transfers in the ponds; and (iii) the set-up of a mathematical model, i.e. the MLLE (Modèle de Lagunage par Lentilles d'eau) through the mass balances approach based on the Petersen’s matrix. The study of the growth kinetics of L. minor was carried out in a growth chamber (phytotron) using a pilot involving initial fresh L. minor biomass and different set of concentrations in nutrient nitrogen (N) and phosphorus (P), light intensity, pH, and temperature. The growth was monitored using the gravimetric methods and digital images processing. The results showed that the growth of L. Minor was optimum for concentrations of N and P of circa 10 mg N-NH4+.L-1 and 1 mg P-PO43-.L-1, respectively, with a maximum growth rate of approximately 0.09 j-1. However, the growth decreased progressively when the respective concentrations of N and P reached approximately 16 mg N-NH4+L-1 and 6 mg P-PO43-.L-1. A possible inhibition due to the excess of substrates might be the cause of such decrease. Moreover, a light intensity greater than 450 μmol.m-².s-1 was potentially harmful for L. minor surviving (growth rate dropped by 60%), though the mortality rate was low (< 0.05 j-1). Characterizing the stoichiometry of L. minor resulted in the formulation of the plant biomol (C88H163O70N10P) and the description of biochemical processes occurring within the ponds, as well as the determination of the conversion rates substrate-biomass in each of these processes. The Lavoisier's principle (conservation of the matter) also was confirmed for the stoichiometric relationship developed for chemical oxygen demands through our experiments. Furthermore, the aeration test assays revealed the influence of the biomass coverage on the gaz/liquid transfers parameters. An exponential decrease of the transfer coefficients, the oxygenation capacity and hourly inputs was associated with increasing coverage rates in both absence and presence of plants. The hypothesis of a main release (about 80%) of oxygen (consumption of carbon dioxide) toward the atmosphere was also confirmed. The third fold of our study was then undertaken based on our findings on the biochemical processes (kinetics and stoichiometry of growth and mortality of plants) and findings on physical processes (gas/liquid transfer) occurring in WSP. A mathematical model, the MLLE, was thus developed and its validity assessed through the equilibrium of the Petersen's matrix. The impact of key nutrients (i.e., nitrogen and phosphorus) on the growth of duckweed, along with the influence of the release of oxygen (consumption carbon dioxide) by the floating macrophytes (L. minor) can be, therefore, thoroughly assessed based on the state variables of the model. Additional simulations using the West® (World Wide Engine for Simulation, Training and Automation) software could help in further calibrating and/or validating the MLLE, and guide in its implementation for industrial purposes. Keywords: Lemna minor, biomass, image processing, nutrient, biomole, gas/liquid transfer, model [less ▲]

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See detailHors-cadre : quand le documentaire ne peut pas tout montrer
Hamers, Jérémy ULg

Scientific conference (2014, December 18)

Detailed reference viewed: 15 (1 ULg)
Peer Reviewed
See detailUncertainty in Training-Image Based Inversion of Hydraulic Head Data Constrained to ERT Data: Workflow and Case Study
Hermans, Thomas ULg; Nguyen, Frédéric ULg; Caers, Jef

Conference (2014, December 18)

In inverse problems, investigating the relationship between data and prior models and the uncertainty related to the posterior distribution of model parameters are as important as matching the data. In ... [more ▼]

In inverse problems, investigating the relationship between data and prior models and the uncertainty related to the posterior distribution of model parameters are as important as matching the data. In recent years, many efforts have been done to assess the posterior distribution of a given problem with reasonable computational costs through inversion techniques such as McMC. The derived posterior distribution is always dependent on the prior distribution. However, most of the studies ignore modeling the prior with realistic uncertainty. In this paper, we propose a workflow to assess the uncertainty of inversion of hydraulic heads data through the addition of electrical resistivity tomography (ERT) constraining data. The workflow is divided in three successive steps: 1) Construction of prior: we generate multiple alternative geological scenarios from literature data (architecture of facies) as well as site specific data (proportions of facies). Spatial uncertainty within each scenario is integrated hierarchically through geostatistics (multiple-point statistics simulation of facies constrained by ERT data as soft data). 2) Validation of prior scenarios: we transform prior facies scenarios into resistivity distribution scenarios through forward and inverse modeling. The scenarios are validated by comparison with field ERT data. The comparison is made through distance calculation and projection into a low dimensional space to calculate the probability of each scenario given field ERT data. 3) Matching dynamical data: we use the probability perturbation method, within each scenario, to integrate hydraulic heads to our models. We account for scenario probabilities, calculated in 2, in determining how many models per scenario we have to consider for building a reliable posterior distribution. As an illustration, the method is applied on a field case study in an alluvial aquifer (Belgium) where we consider prior uncertainty related to the type of elements (gravel channels or bars) and to their size. This study shows the importance of considering the uncertainty of the prior in inverse problems as it has a strong influence on model predictions and decision-making problems. [less ▲]

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See detailModélisation des processus physiques et biologiques dans des fosses septiques et voies de valorisation des boues de vidange:Application à Bujumbura-Burundi
Nsavyimana, Gaston ULg

Doctoral thesis (2014)

Dans les pays en développement (PED) en général et au Burundi en particulier, la problématique de gestion des eaux usées et des déchets solides constitue un enjeu majeur pour les spécialistes et les ... [more ▼]

Dans les pays en développement (PED) en général et au Burundi en particulier, la problématique de gestion des eaux usées et des déchets solides constitue un enjeu majeur pour les spécialistes et les autorités locales. En effet, suite à un manque des stations d'épuration collectives au Burundi, les fosses septiques sont les plus utilisées pour gérer les eaux usées produites. Cependant, les processus qui s'y déroulent ne sont pas encore maîtrisés et la gestion des boues de vidange lorsque ces installations sont remplies, constitue une problématique qui mérite d'être abordée afin de trouver des solutions adaptées, à court et à long terme. Et, suite à une absence des technologies appropriées en matière de gestion des déchets solides, ils sont jetés de manière inadmissible (dans les caniveaux, rivières, places publiques, etc.), et cela peut engendrer à court ou à long terme des nuisances graves, tant pour la santé et l'hygiène publique que pour l'environnement. C’est dans l’optique de contribuer: (i) à l'amélioration de la qualité environnementale; (ii) et à la réduction des risques sanitaires associés à la gestion des déchets liquides et solides à Bujumbura (Burundi), que s’inscrit ce travail de recherche qui porte sur la "Modélisation des processus physiques et biologiques dans des fosses septiques et voies de valorisation des boues de vidange: Application à Bujumbura-Burundi". Différents axes ont ainsi été abordés pour répondre a cet objectif général : (1) la quantification des processus physico-chimiques dans des fosses septiques; (2) la modélisation stœchiométrique, cinétique et mathématique des processus biochimiques; et (3) l'étude des voies de valorisation énergétique des boues de vidange, soit seules (en digestion anaérobie) ou combinées avec des déchets solides fermentescibles (en co-digestion anaérobie). L'étude de quantification des processus physico-chimiques, matérialisables par le phénomène de décantation des particules solides a permis de dégager deux résultats principaux: (i) les effluents d'entrée dans les fosses septiques présentent une bonne décantabilité; (ii) les effluents de sortie de ces ouvrages (107 mg MES/L) ne respectent pas les normes de rejets (30 mg MES/L: cas de la norme Belge). Des dispositifs appropriés pour le traitement des effluents de sortie des fosses septiques (lit filtrant drainé/ou non à flux vertical sur un massif de sable, lit filtrant drainé/ou non à flux vertical sur un massif de zéolithe, lit filtrant horizontal drainé, tertre d’infiltration, tranchée d'épandage ou lit bactérien percolateur) ont été proposés pour palier les insuffisances des puits perdants couramment utilisés au Burundi. L'étude de caractérisation des flux entrant dans des fosses septiques était indispensable pour les modélisations ultérieures (stœchiométrique, cinétique et mathématique) des processus biochimiques et a permis de quantifier, de manière revisitée, la notion d' un équivalent habitant. Ainsi, un équivalent habitant (EH) a été déterminé pour la Belgique et le Burundi en termes de la demande chimique en oxygène (DCO), soit 138,75 ± 20,09 gDCO/EH/j et 117,08 ± 10,09 gDCO/EH/j respectivement. De plus, cette étude a permis de caractériser, par rapport à un équivalent habitant, différents composés chimiques importants contenus dans les flux entrant dans les fosses septiques. Les résultats variaient entre 0,37 ± 0,18 g/EH/j (pour les acides aminés urinaires ) et 43,44 ± 4,35 g/EH/j ( pour glucides), avec des valeurs de 5,00 ± 0,3; 10,15 ± 1,96; 10,6 ± 3,27; 14,7 ± 0,4 et 14,99 ± 1,57 g/EH/j respectivement pour les savons de bain/douche, lipides, azote total, détergent pour lave-linge et protéines. Ces résultats ont contribué à l'élaboration d'une formule "de biomole de substrat complexe" (C23 H49O9N) représentant les eaux usées, utile pour simplifier la modélisation mathématique de fonctionnement des fosses septiques en réduisant le nombre de processus, de variables d’état, d’équations cinétiques associées et des paramètres qui en découlent. La modélisation stœchiométrique des processus biochimiques qui se déroulent dans les fosses septiques, après avoir vérifié que le métabolisme est bien anaérobie, même si des eaux usées éventuellement saturées en O2 entrent quotidiennement dans ce type de dispositifs, a permis de mettre en place un système d’équations qui décrit la stœchiométrie de fonctionnement des fosses septiques. Par ailleurs, dans les pays en développement comme le Burundi, les laboratoires sont moins équipés et ont un accès très limité aux équipements modernes d'analyse usuels (ex., GC ou HPLC ), pour le dosage des acides gras volatils (AGV). A cet effet, nous avons développé et vérifié une nouvelle méthode de dosage des AGV par titrage, efficace et proche de la méthode chromatographique en phase gazeuse. A 99% d'intervalle de confiance, les résultats obtenus à l'aide de cette nouvelle méthode, sont comparables à ceux de la chromatographie en phase gazeuse. La modélisation cinétique a permis de mettre en exergue un modèle de dégradation de la biomole du substrat complexe, qui s'est révélé comparable au modèle cinétique de Monod. Les constantes cinétiques découlant du traitement des données sont dans le cas présent: (i) le taux maximum de croissance spécifique (µmax) égal à 0,0065 j-1; (ii) la constante de demi-saturation de ce substrat combiné synthétique égale à 9,18 g DCO/l ou 4,26 g/l; et (iii) le taux de mortalité égal à 0,0001 j-1. Ces données sont très utiles pour les simulations de fonctionnement des fosses septiques à l'aide d'un logiciel de gestion des ouvrages de traitement des eaux usées (WEST®). Ce travail a également permis de développer un modèle global de fonctionnement des fosses septiques (MFS/DDA ), qui par ailleurs a été présenté suivant le formalisme matriciel de Petersen. Une étude préliminaire de caractérisation détaillée des boues de vidange a montré qu'elles sont presque stabilisées, du point de vue valorisation énergétique. Lorsqu'elles sont digérées seules, elles présentent un faible potentiel méthanogène, soit 2,09 m3 biogaz/m3 de boues fraîches (après deux mois de digestion). Ce biogaz est composé de 71% de CH4 contre 29% de CO2. Ce travail a montré un intérêt de co-digestion anaérobie des boues de vidange avec les déchets solides fermentescibles. A cet effet, un rapport MVSFS/MOVdéchets égal à 0,3 (MOVdéchets étant exprimées en poids sec de déchets et MVSFS en poids sec des boues de vidange) s’est révélé optimal , pour leur meilleure valorisation énergétique, avec une production cumulée maximale de biogaz égal à 12,14 m3biogaz/m3 de mélange gadoues-déchets. La composition moyenne de ce biogaz était de 65,6% en CH4 contre 34,4% en CO2. Mots Clés: Burundi; Assainissement; Fosses septiques; Eaux noires; Eaux grises; Equivalent habitant; Décantation; Digestion anaérobie; Substrat combiné; Acides gras volatils; Modèle stœchiométrique; Modèle cinétique; Matrice de Petersen; Simulations avec WEST®; Boues de vidange; Potentiel méthanogène; Co-digestion anaérobie; Déchets solides fermentescibles. [less ▲]

Detailed reference viewed: 4 (2 ULg)
See detailBelgien- und Deutschlandbilder als Spiegel der ostbelgischen Nachkriegsgesellschaft
Brüll, Christoph ULg

Conference (2014, December 13)

Detailed reference viewed: 7 (0 ULg)
See detailLes médias belges face à la "crise" : acteurs et discours de l'austérité
Geuens, Geoffrey ULg

Conference given outside the academic context (2014)

Detailed reference viewed: 20 (5 ULg)
See detailL’antithèse de la psychopathologie : à propos d’un inexistant
Englebert, Jérôme ULg

Scientific conference (2014, December 12)

Detailed reference viewed: 11 (0 ULg)
Peer Reviewed
See detailAnalphabétisme secondaire, raison cynique et la culture pour tous.
Hamers, Jérémy ULg

Conference (2014, December 12)

Detailed reference viewed: 17 (0 ULg)
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See detailStable isotope ratios reveal trophic niche partitioning among hermit crabs from tropical polyspecific seagrass meadows
Michel, Loïc ULg; Frederich, Bruno ULg; Lavitra, Thierry et al

Poster (2014, December 12)

Polyspecific seagrass meadows are ubiquitous features of tropical coastal zones. These ecosystems are of critical ecological importance, and provide a wide range of socio-economical services to local ... [more ▼]

Polyspecific seagrass meadows are ubiquitous features of tropical coastal zones. These ecosystems are of critical ecological importance, and provide a wide range of socio-economical services to local populations. Meadows however undergo multiple threats linked to human activities (increased nutrient input, overfishing, invertebrate overharvesting, etc.). It is currently hard to assess how seagrass meadows could respond to anthropogenic impacts due to poor knowledge of their functional ecology. In an effort to unravel trophic interactions ruling the food webs associated to seagrass beds of the Toliara Great Reef (SW Madagascar), we studied resource segregation between two common Diogenidae hermit crabs (Dardanus scutellatus and Ciliopagurus tricolor) using stable isotope ratios. Interspecific differences were noted in isotopic composition of carbon (δ13C = -12.22 ± 1.73 ‰ for D. scutellatus, δ13C = -14.55 ± 0.73 ‰ for C. tricolor), nitrogen (δ15N = 4.73 ± 0.53 ‰ for D. scutellatus, δ15N = 5.20 ± 0.61 ‰ for C. tricolor) and sulfur (δ34S = 14.08 ± 2.32 ‰ for D. scutellatus, δ34S = 16.73 ± 1.49 ‰ for C. tricolor), suggesting that the two species do not feed on the same items. In addition, SIBER (Stable Isotope Bayesian Ellipses in R) modeling based on C and N data clearly showed that no overlap was present in the core isotopic niches of the two species. It also indicated that the isotopic niche of D. scutellatus was greater than the one of C. tricolor, implying that the former feeds on a greater number of items than the latter. While hermit crabs are generally considered as omnivorous species, this study highlighted differences in the foraging ecology of D. scutellatus and C. tricolor. These differences could help to limit competition for food between these two species, and facilitate their coexistence in Malagasy seagrass beds. [less ▲]

Detailed reference viewed: 35 (8 ULg)
Peer Reviewed
See detailNegations in Late Egyptian: the general trends. A functional and typological perspective
Winand, Jean ULg

Conference (2014, December 12)

Detailed reference viewed: 7 (1 ULg)