Éditeur(s) : HAL CCSD Springer Verlag/EDP Sciences
Résumé : International audience
Key message: Genetic diversity appears to be unaffected by disturbance in a stand of the light-demanding Neotropical treeV. michelii. Although spatial genetic structure is modified in post-disturbance cohorts, mixing of seeds from different mother trees in canopy gaps appears to efficiently maintain genetic admixture. Context: The interplay between genetic and demographic processes has major consequences on population viability. Population size affects demographic trends, while genetic diversity insures viability by reducing risks of inbreeding depression and by maintaining adaptive potential. Yet, the consequences of increases in census size (as opposed to effective size) on genetic diversity of forest populations are poorly known. Aims: We have studied the structure of genetic diversity in populations of saplings of the light-responsive tree, Virola michelii (Myristicaceae, the nutmeg family), in two plots having undergone different levels of canopy-gap opening disturbance. This allowed us to test the “intermediate disturbance” hypothesis, which generally applies to species diversity, at the intra-specific scale. Methods: Levels and distribution of genetic diversity were compared between plots and between life stages. Sapling parentage was analysed to infer each adult tree’s contribution to regeneration. Results: Genetic diversity was higher, and spatial genetic structure was stronger in the post-disturbance than in the control seedling population. Parentage analysis suggested that a limited number of parents contributed to most of the regeneration, but that efficient mixing of their progeny may have enhanced the diversity of saplings occupying canopy gaps. Conclusion: A mixture of demo-genetic processes may contribute to maintain genetic diversity in spite of, or possibly due to, ecosystem disturbance in V. michelii.
ISSN: 1286-4560

hal-01502942
https://hal-agroparistech.archives-ouvertes.fr/hal-01502942
https://hal-agroparistech.archives-ouvertes.fr/hal-01502942/document
https://hal-agroparistech.archives-ouvertes.fr/hal-01502942/file/art_10.1007_s13595-015-0508-3-1_%7B869D58F4-272C-491F-A903-DAD6CDBDC042%7D.pdf
DOI : 10.1007/s13595-015-0508-3

Éditeur(s) : HAL CCSD
Résumé : International audience
In the area of the link mining, frequent pattern discovery tasks generally consist in the search for subgraphs frequently found in a network or a set of networks. Very recently, new axes of this problem has been proposed through the search for frequent links. Unlike traditional approaches that focus solely on structural regularities, frequent link mining methods exploit both the network structure and the attributes of nodes for extracting regularities in the links existing between node groups that share common characteristics. However, extracting frequent links is still a particularly challenging and computationally intensive issue since it is much dependent on the number of links. In this study, we propose a solution that is able to reduce the computing time by reducing the search to only a subset of of nodes. Experiments were conducted to understand the effects of different thresholds of the subset size on the loss of patterns and the gain in terms of computation time. Our solution proves to be efficient for a rather wide range of thresholds.
Research Challenges in Information Science
Vallence, Spain

hal-00767039
https://hal.archives-ouvertes.fr/hal-00767039
DOI : 10.1109/RCIS.2012.6240432

Éditeur(s) : HAL CCSD
Résumé :  
For a comprehensive evaluation of human influences on the genetic system, the simulation model EGO-GENE was developed. The model combines population genetic and population dynamic processes with forest growth models. The dynamics of genetic structures (single locus and multilocus genotypes up to 200 loci) can be simulated. Spatial and temporal genetic dynamics are included in the model. Overlapping or separated generations can be created and different modes of mating systems can be implemented. The model can be run with empirical and fictitious input data. The simulated genetic structures can be directly analysed with established genetic analysis programmes. An example demonstrates the use of the model far validation of interactions among components of the mating system. Another example demonstrates the applicability of the model in decision-making for seed sampling strategies. The genetic differences between the adult trees and the harvested seeds and the danger of genetic drift regarding to different seed sampling strategies are investigated by use of the genetic distance and the reproductively effective population size.
Silvae genetica

hal-01032083
https://hal.archives-ouvertes.fr/hal-01032083

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Alkali feldspar thermochronologic modeling with the 40Ar/39Ar method has generated marked advances in knowledge of the mechanisms for argon diffusion in feldspars. While the goal in many cases has been to extrapolate the observed and modeled argon behavior in feldspars to natural geological settings, scientific debate surrounding the true feasibility of such extrapolations and indeed, the validity of thermochronologic modeling in itself, have provided much impetus to improve laboratory techniques to test, and increase basic understanding of, argon diffusion. Two cornerstones for the debate over the feasibility of alkali feldspar thermochronology for modeling natural, geologic processes have been: 1. is volume diffusion the main mechanism for argon movement in feldspars? and 2. if volume diffusion is a viable mechanism, does argon then reside in discrete ‘domains' within the feldspar lattice? We describe a study of alkali feldspars from a profile through a well-controlled brittle fault zone in western Norway; the feldspars document argon loss during deformation and strongly suggest the existence of argon ‘domains' within the feldspars, at least during laboratory step heating. The progressive change in the character of argon diffusion is recognizable in the logr/ro diffusion data from the feldspars and is mimicked by physical changes observed optically in the feldspars through progressive degrees of brittle deformation. Modeling results indicate a reduction in size of the biggest domains and the appearance of smaller domains during the strongest stages of deformation. Whether or not this reveals the existence and the transformation of the domain structure in naturo is difficult to prove from our data alone, but interestingly, this behaviour corresponds directly to the physical (optical) appearance of more intense crack networks and subgrains in progressively more brecciated feldspars. Because the thermochronologic histories derived from modeling the feldspar data conform very well to the known tectonic history of the area, the feldspars appear to have successfully retained physical (optical and isotopic) records of episodic tectonic processes operating from ductile through lowtemperature brittle regimes in rocks with a Caledonian history overprinted by several later (younger) geologic events. However, because the ‘cold' brecciation is the last tectonothermal event recorded by these rocks, it is impossible to truly test for the existence of diffusion domains in naturo. Argon loss appears to have been effective only in the most highly brecciated (deformed) samples where the combination of the connected crack network, increased fluid flow and higher temperatures enhanced diffusion via fast diffusion pathways and thus, volume diffusion from the lattice. Only minor argon loss occurred in zones of lower brittle strain, although some development of cracks and brittle features is evident. Independent of the existence of diffusion domains, this study highlights the possible pitfalls when cooling histories are deduced from brecciated feldspars in which age and diffusion charateristics have been decoupled: while the geochronological memory has survived and is identical to that of nonbrecciated feldspars (suggesting no loss and minor effects of deformation), the diffusion characteristics have been completely transposed by brecciation and the appearance of new domains. Modeling feldspars with these latter characteristics would effectively utilise a new feldspar diffusion structure with an ‘old' (relict) age memory.
ISSN: 0016-7037

hal-00198283
https://hal.archives-ouvertes.fr/hal-00198283
https://hal.archives-ouvertes.fr/hal-00198283/document
https://hal.archives-ouvertes.fr/hal-00198283/file/KsparBreccia_Arnaud_Eide_GCA_2000.pdf

Éditeur(s) : Elsevier
Résumé : As top predators of pelagic food webs, large fish naturally bioaccumulate mercury (Hg). Determining Hg burdens in commercialized fish is essential considering the concern about effects of contaminants on human health and the legal thresholds that are therefore set for local consumption and/or exportation. Total Hg levels were measured in the muscular tissue of 183 fish of five commercially important species from the tropical zone of the Western Indian Ocean. All individuals were measured and sexed in order to study the impregnation of Hg with size and sex within each species. Values of Hg found in this part of the Indian Ocean were comparable to Hg in muscular tissue of the same species studied in other areas. The highest Hg levels were noted in Swordfish (Xiphias gladius) caught in waters surrounding Reunion Island (3.97 +/- 2.67 mu g g(-1) dry weight). Following the Swordfish, in decreasing order of Hg content, were the Yellowfin Tuna (Thunnus albacares) and the Skipjack (Katsuwonus pelamis), then the Common Dolphinfish (Coryphaena hippurus) and the Wahoo (Acanthocybium solandri). In the North of the Mozambique Channel, Swordfish had higher Hg levels than Yellowfin Tunas, and Dolphinfish exhibited intermediate Hg levels. The size of a fish was a determining factor of its Hg burden, as was the species. Differences in size-normalized Hg levels were observed between the two study zones for Swordfish and Common Dolphinfish. Sex, in contrast, did not influence Hg levels suggesting that females and males have similar feeding habits. The muscular Hg levels presented here suggest that consumers of fish originating from the Western Indian Ocean should limit themselves to one Swordfish based meal per week, or one fish meal a day if they choose to eat tuna or Common Dolphinfish. (c) 2006 Elsevier B.V. All rights reserved.
The Science of The Total Environment (0048-9697) (Elsevier), 2006-08 , Vol. 366 , N. 2-3 , P. 688-700

Droits : 2006 Elsevier
http://archimer.ifremer.fr/doc/2006/publication-1862.pdf
DOI:10.1016/j.scitotenv.2006.02.006
http://archimer.ifremer.fr/doc/00000/1862/

Éditeur(s) : Université des Antilles Études caribéennes
Résumé : Cet article invite à un examen des enjeux du développement durable dans les petites économies insulaires en développement. Notre propos se décline en trois points. Après avoir rappelé les spécificités de ces entités insulaires (exiguïté, éloignement/isolement, vulnérabilité), nous analysons ensuite les caractéristiques sociétales qui leur sont couramment prêtées (qualité du substrat social : homogénéité culturelle, sociabilité, propension à l’action collective, etc.) et leur contribution à la durabilité du développement. Nous nous interrogeons dès lors sur le caractère résilient de ces déterminants sociaux dans la mesure où ils peuvent permettre la mise en place de projets et de stratégies effectives de développement durable. Enfin, notre réflexion prend appui sur quelques exemples concrets dans la Caraïbe mettant en relation le contexte social local et les actions de développement durable engagées. Selon les cas, ce socle social territorial peut être appréhendé comme un facteur de blocage ou un moteur de développement durable.
Our article deals with sustainable development in the context of small islands developping states (SIDS). Our article unfolds in three steps. First, we diagnose the disadvantages SIDS usually face to (small size, remoteness, vulnerability). Second, we analyse some societal features commonly described as strong characteristics of ‘islandness’ (social links, cultural homogeneity, sociability, propensity to collective action etc.) and their contribution to sustainable development. We then consider these social determinants as factors of resilience. Third, we discuss specific management projects in the Caribbean showing the role of local co-ordination in promoting (or hindering) effective sustainable development strategies.
Guadeloupe
Martinique
Jamaïque

Droits : info:eu-repo/semantics/openAccess
http://journals.openedition.org/etudescaribeennes/3443

Éditeur(s) : HAL CCSD Elsevier
Résumé : We have studied the phase transformation of forsterite to wadsleyite under shear stress at the Earth's transition zone pressure and temperature conditions. Two-step experiments were performed using a multi-anvil press. First, we hot pressed iron-free forsterite at 6 or 11 GPa and 1100 degrees C. Then we deformed a slab of this starting material using a direct simple shear assembly at 16 GPa and 1400 degrees C for 1, 15, 35, 40, or 60 min. Both the starting material and the deformed samples were characterized using optical and scanning electron microscopy including measurements of crystal preferred orientations (CPO) by electron back scattered diffraction (EBSD), transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FTIR). The phase transformation occurs very rapidly, in less than 1 min, and metastable forsterite relics are not observed after deformation. The grain size of wadsleyite is slightly smaller than the forsterite starting material. The water contents obtained from FTIR analyses in forsterite and wadsleyite are 65-124 wt ppm H2O and 114-736 wt ppm H2O, respectively, which are well below water solubility at similar conditions in the presence of free water. Wadsleyite aggregates display weak CPO patterns with [1 0 0] axes concentrated at low angle to the shear direction, [0 1 0] axes perpendicular to the shear plane and nearly random [0 0 1] axes. Only a few dislocations were observed in wadsleyite with TEM. This observation is consistent with the assumption that most dislocations formed during the initial high-stress stages of these stress-relaxation experiments, were consumed in the phase transformation, probably enhancing the transformation rate. CPO patterns vary as a function of the water content: with increasing water content the density of [1 0 0] axes parallel to the shear direction decreases, and the density of [0 0 1] axes increases. Viscoplastic self-consistent modeling of CPO evolution using previously reported glide systems for wadsleyite, i.e., [1 0 0]{0 k 1} and 1/2 (1 1 1){1 0 1}, cannot reproduce the measured CPO, unless the [0 0 1](0 1 0) system, for which dislocations have not been observed by TEM, is also activated. In addition, wadsleyite grain growth suggests the participation of diffusion-assisted processes in deformation. Calculated anisotropies for P and S-waves using measured CPO are always below 1%. This very low anisotropy is due to both the low finite strain achieved in the experiments, which leads to weak wadsleyite CPO, and to the diluting effect of added majorite. The present experiments emphasize the importance of stress, grain size evolution and water content in the forsterite to wadsleyite phase transformation and subsequent deformation in the transition zone.
ISSN: 0031-9201

hal-00617430
https://hal.archives-ouvertes.fr/hal-00617430
DOI : 10.1016/j.pepi.2010.11.001

Éditeur(s) : Terrapub
Résumé : A series of empirical expressions for predicting gas hydrate stability, its volume fraction out of pore space and gas hydrate mass-density were established in different systems in consideration of gas composition (CH4, C2H6, H2S) and salinity (NaCl, seawater), and pore size at temperature between 273.15 and 300 K, based on our gas hydrate thermodynamic model (Sultan et al., 2004b, c). Six of the developed expressions for predicting gas hydrate stability were validated against the available published experimental data and they were also compared with other models. At temperature 273.15 to 290.15 K, the ARDPs (Average Relative Deviation of Pressures between the prediction and the experimental data) have shown that these empirical expressions are in agreement with the experimental data as well as other models, indicating their reliability of predicting gas hydrate stability for these systems. At higher temperatures, the empirical predictions for gas hydrate stability do not well reproduce the experimental data, because they are based on van der Waals model. The empirical expressions for predicting gas hydrate stability in the systems of CH4 + H2S + H2O, CH4 + seawater + poresize, CH4 + H2S + NaCl and CH4 + CO2 + NaCl, and for evaluating gas hydrate fraction and its density need further validation due to lack of available published experimental data. However, the empirical expressions for gas hydrate fraction and its density show that the effects of pore size and salinity are negligible; gas hydrate fraction will increase if methane concentration continuously increases relatively in excess of methane solubility and decreases with pressure within gas hydrate stability zone, which is well consistent with data of natural gas hydrates in Cascadia; gas hydrate density tends to increase with ethane percentage and decrease with pressure.
Geochemical Journal (0016-7002) (Terrapub), 2008-03 , Vol. 42 , N. 2 , P. 163-175

Droits : 2008 TERRAPUB. The Geochemical Society of Japan.
http://archimer.ifremer.fr/doc/2008/publication-4958.pdf
http://archimer.ifremer.fr/doc/00000/4958/

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The lithospheric mantle is intrinsically heterogeneous and anisotropic. These two properties govern the repartition of deformation, controlling intraplate strain localization and development of new plate boundaries. Geophysical and geological observations provide clues on the types, ranges, and characteristic length scales of heterogeneity and anisotropy in the lithospheric mantle. Seismic tomography points to variations in geothermal gradient and hence in rheological behavior at scales of hundreds of km. Seismic anisotropy data substantiate anisotropic physical properties consistent at scales of tens to hundreds of km. Receiver functions imply lateral and vertical heterogeneity at scales < 10 km, which might record gradients in composition or anisotropy. Observations on naturally deformed peridotites establish that compositional heterogeneity and Crystal Preferred Orientations (CPOs) are ubiquitous from the mm to the km scales. These data allow discussing the processes that produce/destroy heterogeneity and anisotropy and constraining the time scales over which they are active. This analysis highlights: (i) the role of deformation and reactive percolation of melts and fluids in producing compositional and structural heterogeneity and the feedbacks between these processes, (ii) the weak mechanical effect of mineralogical variations, and (iii) the low volumes of fine-grained microstructures and difficulty to preserve them. In contrast, olivine CPO and the resulting anisotropy of mechanical and thermal properties are only modified by deformation. Based on this analysis, we propose that strain localization at the plate scale is, at first order, controlled by large-scale variations in thermal structure and in CPO-induced anisotropy. In cold parts of the lithospheric mantle , grain size reduction may contribute to strain localization, but the low volume of fine-grained domains limits this effect.
ISSN: 0040-1951

hal-01277174
https://hal.archives-ouvertes.fr/hal-01277174
DOI : 10.1016/j.tecto.2015.07.026

Éditeur(s) : Elsevier
Résumé : Correlation between DNA microsatellite heterozygosity and growth rate was investigated in two hatchery-propagated stocks of the shrimp Penaeus stylirostris, which had been genetically isolated from wild founders for 17 generations, and from each other for five more generations. presumed demographic history of these populations suggested that they were maintained at small effective population sizes. and this was confirmed by significant changes in allelic frequencies between the two stocks. Despite a small sample size (n = 60) and a small number of loci screened, a significant positive correlation was detected between microsatellite tri-locus heterozygosity and growth rate in one of the two stocks (r = 0.3, P = 0.02). In the other stock (n = 48), the positive correlation was not significant, but the combined test of single locus heterozygote advantage over the three loci was significant (P = 0.005).Use of DNA microsatellite markers, whose selectively neutral status is generally accepted, allowed us to reject the hypothesis of direct overdominance at marker loci as an explanation for an association of growth rate with heterozygosity. The average depression associated with one locus in our case is above or equivalent to the amount observed for a 10% increase of inbreeding in other species. These results suggest that heterozygosity at neutral marker loci is sufficiently well correlated with individual inbreeding coefficients to reveal a significant residual inbreeding load for growth rate in Tahitian P. stylirostris stocks. Inbreeding during hatchery propagation was, thus, insufficient to purge the ancestral load.
Aquaculture (0044-8486) (Elsevier), 2000-04 , Vol. 184 , N. 3-4 , P. 203-219

Droits : 2000 Elsevier Science B.V. All rights reserved
http://archimer.ifremer.fr/doc/2000/publication-753.pdf
DOI:10.1016/S0044-8486(99)00331-2
http://archimer.ifremer.fr/doc/00000/753/

Éditeur(s) : HAL CCSD Wiley
Résumé : The extent of gene dispersal is a fundamental factor of the population and evolutionary dynamics of tropical tree species, but directly monitoring seed and pollen movement is a difficult task. However, indirect estimates of historical gene dispersal can be obtained from the fine-scale spatial genetic structure of populations at drift-dispersal equilibrium. Using an approach that is based on the slope of the regression of pairwise kinship coefficients on spatial distance and estimates of the effective population density, we compare indirect gene dispersal estimates of sympatric populations of 10 tropical tree species. We re-analysed 26 data sets consisting of mapped allozyme, SSR (simple sequence repeat), RAPD (random amplified polymorphic DNA) or AFLP (amplified fragment length polymorphism) genotypes from two rainforest sites in French Guiana. Gene dispersal estimates were obtained for at least one marker in each species, although the estimation procedure failed under insufficient marker polymorphism, limited sample size, or inappropriate sampling area. Estimates generally suffered low precision and were affected by assumptions regarding the effective population density. Averaging estimates over data sets, the extent of gene dispersal ranged from 150 m to 1200 m according to species. Smaller gene dispersal estimates were obtained in species with heavy diaspores, which are presumably not well dispersed, and in populations with high local adult density. We suggest that limited seed dispersal could indirectly limit effective pollen dispersal by creating higher local tree densities, thereby increasing the positive correlation between pollen and seed dispersal distances. We discuss the potential and limitations of our indirect estimation procedure and suggest guidelines for future studies
ISSN: 0962-1083

hal-01031603
https://hal.archives-ouvertes.fr/hal-01031603
DOI : 10.1111/j.1365-294X.2005.02785.x

Éditeur(s) : World Aquaculture Society, Aquaculture 2006
Résumé : Oysters are among the most familiar of all marine invertebrate taxa. However our knowledge of oyster phylogeny and systematics is fragmentary. This is principally due to the plastic growth patterns of these animals, which result in a wide range of overlapping, ecophenotypic variants that greatly reduce the value of analysis based on shell morphology. Besides that, many intentional or accidental anthropogenic transfers have emphasised this situation. In several cases of misclassification or misidentification of oysters, DNA molecular data, have provided valuable new insights on the tracing of introductions or more generally on the phylogeographic relationships between oyster species. We will illustrate this issue with recent case studies from our lab on several flat and cupped oysters: (1) the Crassostrea gigas – Crassostrea angulata couple of Asian species and their successive introductions in Europe, (2) the new species of cupped oysters, Crassostrea honkongensis, described in Hong-Kong and very divergent from the species Crassostrea gigas it was initially supposed to be, (3) the mangrove oyster Crassostrea gasar that was shown not only to be present along the coasts of Western Africa but also along the Atlantic coasts of South America, and (4) the geographic disjunction between Ostreola stentina, described in the Mediterranean Sea, and the genetically closely related species Ostrea aupouria (from New Zealand) and Ostreola equestris (from Mexico Gulf/Atlantic). At the intra specific level, we will focus on one of the main documented case in Europe, the flat oyster, Ostrea edulis. It is a marine bivalve whose natural geographical distribution ranges along the European Atlantic coast from Norway to Morocco, in addition to the Mediterranean and Black Sea. Studies of allozymes, microsatellites and mitochondrial differentiation over the whole range concluded that a significant divergence existed between Mediterranean and Atlantic populations, together with an isolation-by-distance pattern. However, the average mitochondrial haplotypic diversity displayed a high among populations variance, reflecting smaller effective population size in some locations. Additionally, a ten-fold quantitative difference was observed in the same study in Fst between the mitochondrial and the nuclear genomes, which could be due to sex biased differential reproductive success between males and females. In order to further document this hypothesis, two experiments at the population level were conducted. First, brooding females were sampled in a wild population and the number of males fertilizing a given female estimated. Then, parentage analyses were achieved under experimental conditions: successive mass spawnings were collected from a population of potential genitors kept in hatchery, whose genotypes were known, in order to infer a posteriori the relative contribution of each genitor. Moreover, we aimed to better understand the reproduction dynamics of this species. Several patterns of spawning could be distinguished: unique, successive or extended in time. The different parental contributions and reproductive behaviors observed in these experiments are discussed in the context of the hypothesis of a variance in the reproductive success of males and females and consequences in local and temporal reduced effective population sizes.

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/2006/acte-3475.pdf
http://archimer.ifremer.fr/doc/00000/3475/

Éditeur(s) : HAL CCSD Springer-Verlag Berlin Heidelberg
Résumé : International audience
The main biological function of reaction wood is to act as " muscle " for trees, enabling them to control their posture. The key property to achieve this function is the development of high mechanical stress during the formation of reaction wood cells, called " maturation strains ". Actually, reaction wood formation is basically the asymmetric formation of wood around the tree circumference, with higher maturation strains on the side where reaction wood is formed than on the opposite side. This asymmetry enables stems to bend upward or to compensate for the downward bending induced by gravity. At the cross section level, the performance in this biological function is linked not only to the magnitude of this asymmetry but also to an effect of the cross-sectional size (diameter) of the stem. Eccentric growth and variations in wood mechanical stiffness are second order effects that can modify this performance. Differences in maturation strains between reaction and non-reaction woods are related to their specific cell wall structure and composition. The swelling of the cell wall matrix during maturation and the effect of microfibril angle explain the differences in maturation strains between normal and compression wood. However, this mechanism fails in explaining the high maturation shrinkage of tension wood, and several hypotheses at the molecular levels are still under debate. How trees perceive their gravitational disequilibrium is also an open question for physiologists. Integrative biomechanical modelling (from the polymer level to the cell wall, cross section and whole tree levels) enables defining key variables that explain the performance of reaction wood as a system that insures the stem motricity. Maturation strains can be precisely measured only in recently formed wood at the tree surface, but their changes during the whole tree life can also be estimated by retrospective dendrochronological analysis through structural markers of reaction wood. Lastly, wood in living trees ensures general storage, defence, vascular and skeletal functions, that ask general questions about synergies and trade-offs as the structural characteristics of reaction wood can affect all these functions.
The Biology of Reaction Wood

ISBN : 978-3-642-10813-6
hal-01452085
https://hal.archives-ouvertes.fr/hal-01452085
https://hal.archives-ouvertes.fr/hal-01452085/document
https://hal.archives-ouvertes.fr/hal-01452085/file/Chap_Gril_al_Biomechanical_action_biological_functions_2014.pdf

Éditeur(s) : HAL CCSD Wiley
Résumé : Tank bromeliads form a conspicuous, yet neglected freshwater habitat in Neotropical forests. Recent studies driven by interests in medical entomology, fundamental aspects of bromeliad ecology and experimental research on food webs have, however, prompted increasing interest in bromeliad aquatic ecosystems. As yet, there is nothing in the literature about the life histories and environmental drivers of invertebrate population dynamics in tank bromeliads. Based on fortnightly samples taken over oneyear, size frequency plots and individual dry masses allowed us to establish the life cycles and growth rates of the dominant aquatic invertebrates in a common bromeliad species of French Guiana. Linear mixed-effect models and Mantel tests were used to predict changes in density, biomass, and growth rates in relation to temperature, rainfall, humidity and detrital resources. Annual variations in invertebrate densities and biomasses could be described according to three types of distribution: unimodal, bimodal or almost constant. Despite seasonal variations, precipitation, temperature, relative humidity and detritus concentration accounted significantly for changes in density and biomass, but we found no significant responses in growth rates of most invertebrate species. Species rather displayed non-seasonal life cycles with overlapping cohorts throughout the year. There was also a trend for delayed abundance peaks among congeneric species sharing similar functional traits, suggesting temporal partitioning of available resources. Beyond novel knowledge, quantitative information on life histories is important to predict food-web dynamics under the influence of external forcing and self-organisation. Our results suggest that changes in species distribution that will affect population dynamics through biotic interactions in space and/or time could have greater effects on food webs and ecosystem functioning than changes in environmental factors per se.
ISSN: 0046-5070

hal-01607779
https://hal.archives-ouvertes.fr/hal-01607779
DOI : 10.1111/fwb.12862
PRODINRA : 407311

Éditeur(s) : Gauthier-Villars
Résumé : Several models for the evolution of complex life histories have assumed a carrying capacity for both larval and postlarval stages. In addition, the densities of larvae in laboratory experiments are often so high that there is competition for food. Published values for maximal clearance rates and estimated abundances of larvae suggest that these assumptions and experimental conditions are unrealistic for most marine larvae. For most ciliated larvae, maximum clearance rates are at most a few mi of water daily, and their estimated larval concentrations are at most one to several larvae per liter. Therefore these larvae appear to be too scarce for their grazing to affect their food supply. Larvae of most species are also scarce relative to co-occurring planktonic animals that feed on particles in the same size range. Larvae of many species are scarce relative to co-occurring larvae with a similar feeding apparatus. These observations suggest that larvae of most species have a negligible effect on their food supply. Exceptions could occur when a single species of larva dominates the zooplankton; such circumstances appear to be rare, although extreme aggregations of larvae dominated by a single species could be missed by pump or net samples. Analogous but more conjectural arguments can be made for density-dependent attraction of predators to larval prey. These inferences apply to single species, not to meroplanktonic larvae as a whole: in some coastal waters, larvae of benthic invertebrates comprise a large portion of the multicellular planktonic animals. Also, a species' larval growth may be food-limited in many waters, even when the abundance of food is independent of the abundance of its larvae.
Oceanologica Acta (0399-1784) (Gauthier-Villars), 1996 , Vol. 19 , N. 3-4 , P. 399-407

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/00094/20495/18164.pdf
http://archimer.ifremer.fr/doc/00094/20495/

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Two in situ concrete/claystone interfaces were sampled at the laboratory level in the Andra Meuse/Haute Marne (France) Underground Research Laboratory (URL) in order to study five years of interactions between Callovian-Oxfordian (COx) claystone and two cementitious materials (concrete bottom slab and shotcrete on the walls of the main gallery), with a specific focus on sulfur. Combined mineralogical, chemical and sulfur isotopic investigations were carried out to define the degree of the perturbation of the sulfur system in the claystone and in both the cementitious materials. At both interfaces, results show that the main perturbation on the claystone side is the formation of scarce μm-sized gypsum, the sulfur content of which is essentially derived from pyrite oxidation. The distribution of gypsum is highly correlated with the fissure network of the damaged zone due to excavation of the gallery. Its presence is also often associated with a loss of cohesion of the concrete/claystone interface. Due to the small amounts of gypsum and its μm-size, measurements were performed by ion microprobe. Adaptations were needed on account of the reactivity of gypsum and sulfates in general under the beam. The use of ion microprobe analysis provided evidence of high local isotopic heterogeneity that could be attributed to kinetic fractionation effects. Some analyses suggest a minor contribution of dissolved sulfates in pore water of claystone and possibly of concrete. The perturbation on the concrete side is marked by a significant increase in the bulk sulfur content within three millimeters of the interface with the claystone, showing a sulfur gradient from claystone to concrete. The main objective of this work was to define the extent of the chemical and mineralogical perturbations, taking into account in situ URL conditions, i.e. hydrodynamic conditions (shotcrete sprayed on the gallery walls and subjected to ventilation of the galleries), damaged zone of claystone induced by excavation and multi-scale heterogeneity. This identifies the relevant parameters to better constrain predictive reactive transport models of concrete/claystone interactions at a realistic scale.
ISSN: 0079-1946

hal-01055790
https://hal-brgm.archives-ouvertes.fr/hal-01055790
DOI : 10.1016/j.pce.2014.01.003

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Mantle noble gases record important and ancient isotopic heterogeneities, which fundamentally influence our understanding of mantle geodynamics, yet these heterogeneities are difficult to fully interpret without understanding the basic mechanisms of noble gas storage and transport in mantle minerals. A series of annealing experiments that mimic mantle conditions (i.e. sub-solidus with natural, polycrystalline, texturally equilibrated olivines at low noble gas partial pressures) show that intergranular interfaces (grain boundaries) are major hosts for noble gases in the mantle, and that interfaces can dramatically fractionate noble gases from their radio-parents (U + Th and K). Therefore, noble gas isotopic heterogeneities in the mantle could result from grain size variations. Fine-grained lithologies (mylonites and ultramylonites, for example) with more grain boundaries will have lower U/3He ratios (compared to a coarse grained equivalent), which, over time, will preserve higher 3He/4He ratios. As predicted by theory of points defect diffusivity, these results show that noble gas diffusion along interfaces is different from those in the grain lattice itself at low temperatures. However, for grain size relevant of the Earth's mantle, the resulting effective correlated activation energies (Ea)(Ea) and pre-exponential factors (Do/a2)(Do/a2) produce similar diffusivities at mantle temperatures for interface- and lattice-hosted helium. Therefore, grain boundaries do not significantly affect helium transport at mantle conditions and length scales.
ISSN: 0012-821X

hal-01236013
https://hal.archives-ouvertes.fr/hal-01236013
DOI : 10.1016/j.epsl.2015.08.024

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
Hydrogen can be stored in the structure of nominally anhydrous minerals as point defects, and these impurities substantially modify many physical properties of Earth's mantle minerals. However, mantle rocks are composed of mineral grains separated by grain boundaries and interphase grains boundaries. Therefore, as a potential hydrogen reservoir, grain boundaries should be given proper attention. Here, I report an experimental investigation into hydrogen diffusion through grain boundaries in polycrystalline aggregates Sintering and diffusion experiments were performed using a gas-medium high-pressure vessel at under pressure of 300 MPa and over a temperature range of 900-1,250 degrees C. The diffusion assembly consisted of a polycrystalline cylinder of aluminous spinel + olivine crystals with a talc cylinder as the main hydrogen source. A Ni capsule was used to buffer the oxygen fugacity at Ni-NiO Experimental durations varied from 5 min to 5 h. The presence of hydrogen in the crystals was measured by Fourier-transform infrared spectroscopy. The calculation of the diffusion coefficients was based on the estimation of the characteristic distance. The absence or presence of hydrogen recorded by the 'hydrogen sensor' olivines embedded in the aggregate allows the estimation of bounds on this characteristic distance. Results presented here suggest that hydrogen effective diffusion coefficients are only one order of magnitude faster (similar to 10(-9) m(2)s(-1) at 1,000 degrees C) than in an olivine single crystal along the [100] axis. Resulting diffusion coefficients for hydrogen in grain boundary are four orders of magnitude faster than in a single crystal, but this diffusivity is not fast enough to affect hydrogen mobility in mantle rocks with grain sizes greater than similar to 1 mm. Thus, very limited chemical homogenization would occur using grain boundaries diffusion in mantle hydrous peridotite for incompatible and volatile element, such as hydrogen.
ISSN: 0010-7999

hal-00564353
https://hal.archives-ouvertes.fr/hal-00564353
DOI : 10.1007/s00410-010-0512-4

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
From outcrops located in Provence (South-East France), we describe the distribution, the microstructures, and the petrophysical properties of deformation band networks related to both contractional and extensional tectonic events. In contraction, pervasively distributed networks of reverse-sense compactional shear bands are observed in all folded sand units of the foreland, whereas localized networks of clustered reverse-sense shear bands are only observed close to a large-scale thrust. In extensional setting, networks of clustered normal-sense shear bands are generally observed adjacent to map-scale faults (100 m–10 km scale), although some randomly distributed bands are also observed between these faults. Normal-sense cataclastic faults, i.e. zone of deformation bands containing a localized slip-surface, are also observed to be restricted to sand units, suggesting that faults initiated in the sands during extension, but not during contraction. Shear bands and faults show cataclastic microstructures with high-permeability reduction whereas compactional shear bands show crush microbreccia or protocataclastic microstructures with moderate permeability reduction. This basin-scale analysis underlines the major role of tectonic settings (thrust-fault versus normal-fault andersonian-stress regime) and the influence of inherited large-scale faults on the formation/localization of low-permeability shear bands. We also provide a geometrical analysis of the band network properties (spacing, thickness, shear/compaction ratio, degree of cataclasis, petrophysical properties) with respect to the median grain size, porosity and grain sorting of host sand. This analysis suggests that grain size, although less important than stress-state conditions and the presence of large-scale faults, has a non-negligible effect on band network geometry. No correlations are observed between the grain sorting, porosity and band network geometry.
ISSN: 0264-8172

hal-01116421
https://hal.archives-ouvertes.fr/hal-01116421
DOI : 10.1016/j.marpetgeo.2013.12.020

Éditeur(s) : HAL CCSD American Geophysical Union
Résumé : International audience
Both flow field heterogeneity and mass transfer between mobile and immobile domains have been studied separately for explaining observed anomalous transport. Here we investigate non-Fickian transport using high-resolution 3-D X-ray microtomographic images of Berea sandstone containing microporous cement with pore size below the setup resolution. Transport is computed for a set of representative elementary volumes and results from advection and diffusion in the resolved macroporosity (mobile domain) and diffusion in the microporous phase (immobile domain) where the effective diffusion coefficient is calculated from the measured local porosity using a phenomenological model that includes a porosity threshold ( inline image) below which diffusion is null and the exponent n that characterizes tortuosity-porosity power-law relationship. We show that both flow field heterogeneity and microporosity trigger anomalous transport. Breakthrough curve (BTC) tailing is positively correlated to microporosity volume and mobile-immobile interface area. The sensitivity analysis showed that the BTC tailing increases with the value of inline image, due to the increase of the diffusion path tortuosity until the volume of the microporosity becomes negligible. Furthermore, increasing the value of n leads to an increase in the standard deviation of the distribution of effective diffusion coefficients, which in turn results in an increase of the BTC tailing. Finally, we propose a continuous time random walk upscaled model where the transition time is the sum of independently distributed random variables characterized by specific distributions. It allows modeling a 1-D equivalent macroscopic transport honoring both the control of the flow field heterogeneity and the multirate mass transfer between mobile and immobile domains.
ISSN: 0043-1397

hal-01278285
https://hal.archives-ouvertes.fr/hal-01278285
DOI : 10.1002/2015WR017645