Éditeur(s) : HAL CCSD Springer Verlag/EDP Sciences
Résumé : Le développement de modèles de dynamique forestière adaptés aux forêts tropicales humides est compliqué par la très grande diversité spécifique caractérisant ces forêts. Les modélisateurs ont souvent eu recours, pour simplifier le problème, à des techniques de regroupement d'espèces. Il existe des méthodes diverses de regroupement, qui relèvent de trois grands types de stratégie : (i) stratégie écologique subjective, (ii) stratégie écologique basée sur l'analyse de données, (iii) stratégie des processus de dynamique populationnelle. Dans le cadre des deux premières stratégies, une espèce est affectée à un groupe et un seul alors que dans le cadre de la troisième, des groupes d'espèces sont définis pour chacun des processus de dynamique (recrutement, croissance, mortalité) pris séparément, et chaque espèce est affectée à trois groupes. Dans la littérature, on trouve peu d'exemples de congruence ou de convergence entre les groupes définis par ces différentes méthodes. Ceci peut être expliqué par l'indépendance existant entre les caractères utilisés pour fabriquer tel ou tel groupe, ou encore par la grande variabilité intra-spécifique de ces caractères. Nous argumentons et concluons sur le fait que le recours à la stratégie des processus de dynamique paraît être la meilleure pour construire des groupes d'espèces adaptés à la prédiction de la dynamique des forêts tropicales.
ISSN: 1286-4560

hal-01032060
https://hal.archives-ouvertes.fr/hal-01032060
DOI : 10.1051/forest:2005084

Éditeur(s) : HAL CCSD Wiley
Résumé : International audience
Our understanding of the contribution of interspecific interactions to functional diversity in nature lags behind our knowledge of spatial and temporal patterns. Although two-species mutualisms are found in all types of ecosystems, the study of their ecological influences on other community members has mostly been limited to third species, while their influence on entire communities remains largely unexplored. 2. We hypothesized that mutualistic interactions between two respective ant species and an epiphyte mediate the biological traits composition of entire invertebrate communities that use the same host plant, thereby affecting food webs and functional diversity at the community level. 3. Aechmea mertensii (Bromeliaceae) is both a phytotelm ('plant-held water') and an ant-garden epiphyte. We sampled 111 bromeliads (111 aquatic invertebrate communities) associated with either the ant Pachycondyla goeldii or Camponotus femoratus. The relationships between ants, bromeliads and invertebrate abundance data were examined using a redundancy analysis. Biological traits information for invertebrates was structured using a fuzzy-coding technique, and a co-inertia analysis between traits and abundance data was used to interpret functional differences in bromeliad ecosystems. 4. The vegetative traits of A. mertensii depended on seed dispersion by C. femoratus and P. goeldii along a gradient of local conditions. The ant partner selected sets of invertebrates with traits that were best adapted to the bromeliads' morphology, and so the composition of the biological traits of invertebrate phytotelm communities depends on the identity of the ant partner. Biological traits suggest a bottom-up control of community structure in C. femoratus-associated phytotelmata and a greater structuring role for predatory invertebrates in P. goeldii-associated plants. 5. This study presents new information showing that two-species mutualisms affect the functional diversity of a much wider range of organisms. Most biological systems form complex networks where nodes (e. g. species) are more or less closely linked to each other, either directly or indirectly, through intermediate nodes. Our observations provide community-level information about biological interactions and functional diversity, and perspectives for further observations intended to examine whether large-scale changes in interacting species/community structure over broad geographical and anthropogenic gradients affect ecosystem functions.
ISSN: 0269-8463

hal-00817509
https://hal.archives-ouvertes.fr/hal-00817509

Éditeur(s) : HAL CCSD Public Library of Science
Résumé : International audience
Little is known of how linkage patterns between species change along environmental gradients. The small, spatially discrete food webs inhabiting tank-bromeliads provide an excellent opportunity to analyse patterns of community diversity and food-web topology (connectance, linkage density, nestedness) in relation to key environmental variables (habitat size, detrital resource, incident radiation) and predators: prey ratios. We sampled 365 bromeliads in a wide range of understorey environments in French Guiana and used gut contents of invertebrates to draw the corresponding 365 connectance webs. At the bromeliad scale, habitat size (water volume) determined the number of species that constitute food-web nodes, the proportion of predators, and food-web topology. The number of species as well as the proportion of predators within bromeliads declined from open to forested habitats, where the volume of water collected by bromeliads was generally lower because of rainfall interception by the canopy. A core group of microorganisms and generalist detritivores remained relatively constant across environments. This suggests that (i) a highly-connected core ensures food-web stability and key ecosystem functions across environments, and (ii) larger deviations in food-web structures can be expected following disturbance if detritivores share traits that determine responses to environmental changes. While linkage density and nestedness were lower in bromeliads in the forest than in open areas, experiments are needed to confirm a trend for lower food-web stability in the understorey of primary forests.
PLoS ONE

hal-00913931
https://hal.archives-ouvertes.fr/hal-00913931
https://hal.archives-ouvertes.fr/hal-00913931/document
DOI : 10.1371/journal.pone.0071735
OATAO : 10204

Éditeur(s) : HAL CCSD European Geosciences Union
Résumé : Xylem density is a physical property of wood that varies between individuals, species and environments. It reflects the physiological strategies of trees that lead to growth, survival and reproduction. Measurements of branch xylem density, ρx, were made for 1653 trees representing 598 species, sampled from 87 sites across the Amazon basin. Measured values ranged from 218 kg m−3 for a Cordia sagotii (Boraginaceae) from Mountagne de Tortue, French Guiana to 1130 kg m−3 for an Aiouea sp. (Lauraceae) from Caxiuana, Central Pará, Brazil. Analysis of variance showed significant differences in average ρx across regions and sampled plots as well as significant differences between families, genera and species. A partitioning of the total variance in the dataset showed that species identity (family, genera and species) accounted for 33% with environment (geographic location and plot) accounting for an additional 26%; the remaining "residual" variance accounted for 41% of the total variance. Variations in plot means, were, however, not only accountable by differences in species composition because xylem density of the most widely distributed species in our dataset varied systematically from plot to plot. Thus, as well as having a genetic component, branch xylem density is a plastic trait that, for any given species, varies according to where the tree is growing in a predictable manner. Within the analysed taxa, exceptions to this general rule seem to be pioneer species belonging for example to the Urticaceae whose branch xylem density is more constrained than most species sampled in this study. These patterns of variation of branch xylem density across Amazonia suggest a large functional diversity amongst Amazonian trees which is not well understood.
ISSN: 1726-4170

hal-01032137
https://hal.archives-ouvertes.fr/hal-01032137

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : In habitat mosaics, plant populations face environmental heterogeneity over short geographical distances. Such steep environmental gradients can induce ecological divergence. Lowland rainforests of the Guiana Shield are characterized by sharp, short-distance environmental variations related to topography and soil characteristics (from waterlogged bottomlands on hydromorphic soils to well-drained terra firme on ferralitic soils). Continuous plant populations distributed along such gradients are an interesting system to study intrapopulation divergence at highly local scales. This study tested (1) whether conspecific populations growing in different habitats diverge at functional traits, and (2) whether they diverge in the same way as congeneric species having different habitat preferences. Phenotypic differentiation was studied within continuous populations occupying different habitats for two congeneric, sympatric, and ecologically divergent tree species (Eperua falcata and E. grandiflora, Fabaceae). Over 3000 seeds collected from three habitats were germinated and grown in a common garden experiment, and 23 morphological, biomass, resource allocation and physiological traits were measured. In both species, seedling populations native of different habitats displayed phenotypic divergence for several traits (including seedling growth, biomass allocation, leaf chemistry, photosynthesis and carbon isotope composition). This may occur through heritable genetic variation or other maternally inherited effects. For a sub-set of traits, the intraspecific divergence associated with environmental variation coincided with interspecific divergence. The results indicate that mother trees from different habitats transmit divergent trait values to their progeny, and suggest that local environmental variation selects for different trait optima even at a very local spatial scale. Traits for which differentiation within species follows the same pattern as differentiation between species indicate that the same ecological processes underlie intra- and interspecific variation.
ISSN: 0305-7364

hal-01032430
https://hal.archives-ouvertes.fr/hal-01032430
DOI : 10.1093/aob/mct176

Éditeur(s) : HAL CCSD Elsevier
Résumé : Rh (Rhesus) is a major blood group system in man, which is clinically significant in transfusion medicine. Rh antigens are carried by an oligomer of two major erythroid specific polypeptides, the Rh (D and CcEe) proteins and the RhAG glycoprotein, that shared a common predicted structure with 12 transmembrane a-helices (M0 to M11). Non erythroid homologues of these proteins have been identified (RhBG and RhCG), notably in diverse organs specialized in ammonia production and excretion, such as kidney, liver and intestine. Phylogenetic studies and experimental evidence have shown that these proteins belong to the Amt/Mep/Rh protein superfamily of ammonium/methylammonium permease, but another view suggests that Rh proteins might function as CO2 gas channels. Until recently no information on the structure of these proteins were available. However, in the last two years, new insight has been gained into the structural features of Rh proteins (through the determination of the crystal structures of bacterial AmtB and archeaebacterial Amt-1. Here, models of the subunit and oligomeric architecture of human Rh proteins are proposed, based on a refined alignment with and crystal structure of the bacterial ammonia transporter AmtB, a member of the Amt/ Mep/Rh superfamily. This alignment was performed considering invariant structural features, which were revealed through Hydrophobic Cluster Analysis, and led to propose alternative predictions for the less conserved regions, particularly in the N-terminal sequences. The Rh models, on which an additional Rh-specific, N-terminal helix M0 was tentatively positioned, were further assessed through the consideration of biochemical and immunochemical data, as well as of stereochemical and topological constraints. These models highlighted some Rh specific features that have not yet been reported. Among these, are the prediction of some critical residues, which may play a role in the channel function, but also in the stability of the subunit structure and oligomeric assembly. These results provide a basis to further understand the structure/function relationships of Rh proteins, and the alterations occurring in variant phenotypes.
ISSN: 1246-7820

hal-00068842
https://hal.archives-ouvertes.fr/hal-00068842

Éditeur(s) : HAL CCSD
Résumé : For ecology scientists, spatial statistics are a set of tools allowing characterization of the structure of a point set, for instance a map of trees in a forest plot. This structure is defined implicitly as a departure from complete spatial randomness (CSR), the result of a Poisson point process. Inhomogeneity of the process and non-independence of points are its causes. As they cannot be disentangled by analyzing the data, so-called "spatial concentration" or "aggregation" (evenness due to repulsion also exists but is actually rare) usually concerns non-independence while intensity is assumed as known. The literature of point processes and measures of spatial structures is reviewed to clarify concepts and choices. The purpose of this thesis was to produce methodological enhancements. Its main results are: * A test for the most used statistic, Ripley's K function, against the null hypothesis of CSR. It can replace Monte-Carlo simulations used until now in the literature. * An extension of K to inhomogeneous processes, within a typology of available statistics (absolute, relative and topographic measures). When data is available as number of objects per zones (say a number of tree in each forest plot) rather than their exact position, information theory is used to define a general framework allowing to characterize spatial structure (of species) and diversity (of plots) as two aspects of a single measure of inequality. This framework is applied to Shannon's index of biodiversity to derive a self-sufficient definition of beta diversity, its calculation independently from the difference between gamma and alpha diversity, and a statistical test of significance against the null hypothesis that plots are samples of the same community. The way is paved for other applications to measures of diversity and spatial structures. As a conclusion, it appears clear that pattern characterization tools are a first step to deal with ecological questionings. Their development is still a matter of research. Yet, they are far from sufficient to address ecological processes as point processes ignore the temporal aspect of object locations.
Les statistiques spatiales sont pour les écologues un ensemble d'outils permettant de caractériser la structure d'un semis de points, par exemple une carte représentant des emplacements des arbres dans une parcelle de forêt. Cette structure est définie implicitement comme un écart à semis complètement aléatoire, résultat d'un processus de Poisson. L'hétérogénéité du processus ponctuel dont le semis de points est une réalisation et la non-indépendance des points en sont les causes indiscernables, ce qui amène généralement à supposer l'intensité du processus connu et nommer " concentration spatiale " ou " agrégation " (la régularité spatiale est possible, mais rare en pratique) la non-indépendance. Une revue de la littérature des processus ponctuels et des mesures de structures spatiales est fournie pour clarifier les concepts et les choix. L'objectif de ce travail de thèse était de produire des améliorations méthodologiques. Ses résultats principaux sont : * L'établissement d'un test pour la principale statistique utilisée, la fonction K de Ripley, permettant de s'affranchir de la méthode de Monte-Carlo utilisée dans la littérature pour rejeter l'hypothèse nulle d'un processus complètement aléatoire. * L'extension de K aux processus hétérogènes, dans le cadre d'une typologie claire des statistiques (absolues, relatives, topographiques). Lorsque la position exacte des objets n'est pas connue, mais que des effectifs par zone sont disponibles (par exemple des nombres d'arbres par parcelle), la théorie de l'information est utilisée pour définir un cadre général permettant de caractériser la structure spatiale (des espèces dans les parcelles) et la diversité (des parcelles, en termes d'espèces) comme deux aspects d'une même mesure d'inégalité. Ce cadre est appliqué à l'indice de biodiversité de Shannon pour définir clairement la mesure de diversité bêta, son calcul direct indépendamment de la différence entre diversités gamma et alpha, et fournir un test statistique de non nullité. La voie est ouverte pour l'application à d'autres mesures de diversité et de structure spatiale. En conclusion, il semble clair que ces outils de caractérisation sont un premier pas pour traiter les questions écologiques, leur développement étant toujours du domaine de la recherche. Ils sont cependant très insuffisants pour répondre à des questions liées aux processus écologiques, assez éloignés des processus ponctuels qui ignorent l'aspect temporel de l'installation des objets.
https://pastel.archives-ouvertes.fr/pastel-00540327

NNT : 2010AGPT0075
pastel-00540327
https://pastel.archives-ouvertes.fr/pastel-00540327
https://pastel.archives-ouvertes.fr/pastel-00540327/document
https://pastel.archives-ouvertes.fr/pastel-00540327/file/13_Marcon2010.pdf

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : Understanding the ability of ecosystem processes to resist to and to recover from disturbances is critical to sustainable land use. However, the spatial variability of the stability has rarely been addressed. Here, we investigated the functional stability of a soil microbial process for 24 soils collected from adjacent locations from a 0.3 ha tropical rainforest plot in Paracou, French Guiana. The 24 locations were characterized regarding soil chemical and biological (microbial diversity) parameters and forest structure. The corresponding soils were submitted to an experimental transient heat disturbance during a microcosm experiment. The response of the respiration process was followed using substrate-induced respiration (SIR). The response of soil SIR to heat disturbance varied widely between samples. The variability of the SIR response increased just after the disturbance, and a global rather homogeneous decrease in SIR rates was observed 15 and 30 days after. The stability of SIR in response to heat disturbance could not be related to either the genetic or the metabolic diversity of the microbial community. The initial level of SIR before the disturbance was the soil variable that best correlated with the impact of the disturbance: the soil locations with the highest initial SIR rates were the most affected 15 and 30 days after the heat disturbance. Such a heterogeneous response suggests that the response of soil processes to a disturbance will be difficult to assess from only local-scale analyses and highlights the need for spatial explicitness in understanding biogeochemical processes.
ISSN: 1439-0108

hal-01204209
https://hal.archives-ouvertes.fr/hal-01204209
DOI : 10.1007/s11368-012-0528-7
PRODINRA : 214444

Éditeur(s) : HAL CCSD Wiley
Résumé : Negative density dependence (NDD) and environmental filtering (EF) shape community assembly, but their relative importance is poorly understood. Recent studies have shown that seedlings mortality risk is positively related to the phylogenetic relatedness of neighbours. However, natural enemies, whose depredations often cause NDD, respond to functional traits of hosts rather than phylogenetic relatedness per se. To understand the roles of NDD and EF in community assembly, we assessed the effects on seedling mortality of functional similarity, phylogenetic relatedness and stem density of neighbouring seedlings and adults in a species-rich tropical forest. Mortality risks increased for common species when their functional traits departed substantially from the neighbourhood mean, and for all species when surrounded by close relatives. This indicates that NDD affects community assembly more broadly than does EF, and leads to the tentative conclusion that natural enemies respond to phylogenetically correlated traits. Our results affirm the prominence of NDD in structuring species-rich communities.
ISSN: 1461-023X

hal-01032429
https://hal.archives-ouvertes.fr/hal-01032429
DOI : 10.1111/j.1461-0248.2011.01705.x

Éditeur(s) : HAL CCSD
Résumé : One critical challenge for plants is to maintain an adequate nutrient supply under fluctuating environmental conditions. This is particularly true for epiphytic species that have limited or no access to the pedosphere and often live in harsh climates. Bromeliads have evolved key innovations such as epiphytism, water-absorbing leaf trichomes, tank habit and Crassulacean acid metabolism (CAM) photosynthesis that enable them to survive under various environmental conditions. Bromeliads encompass diverse ecological types that live on different substrates (they can be terrestrial, epilithic or epiphytic) and vary in their ability to retain water (they can be tank-forming or tankless) and photosynthetic pathway (i.e. C3 or CAM). In this review, we outline the nutritional modes and specializations that enable bromeliads to thrive in a wide range of nutrient-poor (mostly nitrogen-depleted) environments.Important FindingsBromeliads have evolved a great diversity of morphologies and functional adaptations leading to the existence of numerous nutritional modes. Focusing on species that have absorptive foliar trichomes, we review evidence that bromeliads have evolved multi-faceted nutritional strategies to respond to fluctuations in the supply of natural nitrogen (N). These plants have developed mutualistic associations with many different and functionally diverse terrestrial and aquatic microorganisms and metazoans that contribute substantially to their mineral nutrition and, thus, their fitness and survival. Bacterial and fungal microbiota-assisted N provisioning, protocarnivory, digestive mutualisms and myrmecotrophic pathways are the main strategies used by bromeliads to acquire nitrogen. The combination of different nutritional pathways in bromeliads represents an important adaptation enabling them to exploit nutrient-poor habitats. Nonetheless, as has been shown for several other vascular plants, multiple partners are involved in nutrient acquisition indicating that there have been convergent adaptations to nutrient scarcity. Finally, we point out some gaps in the current knowledge of bromeliad nutrition that offer fascinating research opportunities.
ISSN: 1752-9921

hal-01532637
https://hal.archives-ouvertes.fr/hal-01532637
DOI : 10.1093/jpe/rtv052
PRODINRA : 384521

Éditeur(s) : Elsevier
Résumé : We investigated the influence of bioturbation by macrofauna on the vertical distribution of living (stained) benthic foraminifera in marine intertidal sediments. We investigated the links between macrofaunal bioturbation and foraminiferal distribution, by sampling from stations situated on a gradient of perturbation by oyster-farming, which has a major effect on benthic faunal assemblages. Sediment cores were collected on the French Atlantic coast, from three intertidal stations: an oyster farm, an area without oysters but affected by oyster biodeposits, and a control station. Axial tomodensitometry (CT-scan) was used for three-dimensional visualization and two-dimensional analysis of the cores. Biogenic structure volumes were quantified and compared between cores. We collected the macrofauna, living foraminifera, shells and gravel from the cores after scanning, to validate image analysis. We did not investigate differences in the biogenic structure volume between cores. However, biogenic structure volume is not necessarily proportional to the extent of bioturbation in a core, given that many biodiffusive activities cannot be detected on CT-scans. Biodiffusors and larger gallery-diffusors were abundant in macrofaunal assemblage at the control station. By contrast, macrofaunal assemblages consisted principally of downward-conveyors at the two stations affected by oyster farming. At the control station, the vertical distribution of biogenic structures mainly built by the biodiffusor Scorbicularia plana and the large gallery-diffusor Hediste diversicolor was significantly correlated with the vertical profiles of living foraminifera in the sediment, whereas vertical distributions of foraminifera and downward-conveyors were not correlated at the station affected by oyster farming. This relationship was probably responsible for the collection of foraminifera in deep sediment layers (> 6 cm below the sediment surface) at the control station. As previously suggested for other species, oxygen diffusion may occur via the burrows built by S. plana and H. diversicolor, potentially increasing oxygen penetration and providing a favorable microhabitat for foraminifera in terms of oxygen levels. By contrast, the absence of living foraminifera below 6 cm at the stations affected by oyster farming was probably associated with a lack of biodiffusor and large gallery-diffusor bioturbation. Our findings suggest that the effect of macrofaunal bioturbation on the vertical distribution of foraminiferal assemblages in sediments depends on the effects of the macrofauna on bioirrigation and sediment oxidation, as deduced by Eh values, rather than on the biogenic structure volume produced by macrofauna. The loss of bioturbator functional diversity due to oyster farming may thus indirectly affect infaunal communities by suppressing favorable microhabitats produced by bioturbation.
Journal of Experimental Marine Biology and Ecology (0022-0981) (Elsevier), 2009-03 , Vol. 371 , N. 1 , P. 20-33

Droits : 2009 Elsevier B.V. All rights reserved.
http://archimer.ifremer.fr/doc/2009/publication-6146.pdf
DOI:10.1016/j.jembe.2008.12.012
http://archimer.ifremer.fr/doc/00000/6146/

Éditeur(s) : HAL CCSD Wiley-Blackwell
Résumé :  
1. Despite considerable interest in the application of plant functional traits to questions of community assembly and ecosystem structure and function, there is no consensus on the appropriateness of sampling designs to obtain plot-level estimates in diverse plant communities. 2. We measured 10 plant functional traits describing leaf and stem morphology and ecophysiology for all trees in nine 1-ha plots in terra firme lowland tropical rain forests of French Guiana (N = 4709). 3.We calculated, by simulation, the mean and variance in trait values for each plot and each trait expected under seven sampling methods and a range of sampling intensities. Simulated sampling methods included a variety of spatial designs, as well as the application of existing data base values to all individuals of a given species. 4. For each trait in each plot, we defined a performance index for each sampling design as the proportion of resampling events that resulted in observed means within 5% of the true plot mean, and observed variance within 20%of the true plot variance. 5. The relative performance of sampling designs was consistent for estimations of means and variances. Data base use had consistently poor performance for most traits across all plots, whereas sampling one individual per species per plot resulted in relatively high performance. We found few differences among different spatial sampling strategies; however, for a given strategy, increased intensity of sampling resulted in markedly improved accuracy in estimates of trait mean and variance. 6. We also calculated the financial cost of each sampling design based on data from our 'every individual per plot' strategy and estimated the sampling and botanical effort required. The relative performance of designs was strongly positively correlated with relative financial cost, suggesting that sampling investment returns are relatively constant. 7. Our results suggest that trait sampling for many objectives in species-rich plant communities may require the considerable effort of sampling at least one individual of each species in each plot, and that investment in complete sampling, though great, may be worthwhile for at least some traits.
Functional Ecology

hal-01032175
https://hal.archives-ouvertes.fr/hal-01032175
DOI : 10.1111/j.1365-2435.2009.01600.x

Éditeur(s) : HAL CCSD Springer Verlag/EDP Sciences
Résumé : Key messageWe review the recent findings on the influence of drought on tree mortality, growth or ecosystem functioning in tropical rainforests. Drought plays a major role in shaping tropical rainforests and the response mechanisms are highly diverse and complex. The numerous gaps identified here require the international scientific community to combine efforts in order to conduct comprehensive studies in tropical rainforests on the three continents. These results are essential to simulate the future of these ecosystems under diverse climate scenarios and to predict the future of the global earth carbon balance.[br/]ContextTropical rainforest ecosystems are characterized by high annual rainfall. Nevertheless, rainfall regularly fluctuates during the year and seasonal soil droughts do occur. Over the past decades, a number of extreme droughts have hit tropical rainforests, not only in Amazonia but also in Asia and Africa. The influence of drought events on tree mortality and growth or on ecosystem functioning (carbon and water fluxes) in tropical rainforest ecosystems has been studied intensively, but the response mechanisms are complex.[br/]AimsHerein, we review the recent findings related to the response of tropical forest ecosystems to seasonal and extreme droughts and the current knowledge about the future of these ecosystems.[br/]ResultsThis review emphasizes the progress made over recent years and the importance of the studies conducted under extreme drought conditions or in through-fall exclusion experiments in understanding the response of these ecosystems. It also points to the great diversity and complexity of the response of tropical rainforest ecosystems to drought.[br/]ConclusionThe numerous gaps identified here require the international scientific community to combine efforts in order to conduct comprehensive studies in tropical forest regions. These results are essential to simulate the future of these ecosystems under diverse climate scenarios and to predict the future of the global earth carbon balance.
ISSN: 1286-4560

hal-01269438
https://hal.archives-ouvertes.fr/hal-01269438
DOI : 10.1007/s13595-015-0522-5
PRODINRA : 338568

Éditeur(s) : HAL CCSD Wiley-Blackwell
Résumé :  
Cross-species analyses of plant functional traits have shed light on factors contributing to differences in performance and distribution, but to date most studies have focused on either leaves or stems. We extend these tissue-specific analyses of functional strategy towards a whole-plant approach by integrating data on functional traits for 13 448 leaves and wood tissues from 4672 trees representing 668 species of Neotropical trees. Strong correlations amongst traits previously defined as the leaf economics spectrum reflect a tradeoff between investments in productive leaves with rapid turnover vs. costly physical leaf structure with a long revenue stream. A second axis of variation, the 'stem economics spectrum', defines a similar tradeoff at the stem level: dense wood vs. high wood water content and thick bark. Most importantly, these two axes are orthogonal, suggesting that tradeoffs operate independently at the leaf and at the stem levels. By simplifying the multivariate ecological strategies of tropical trees into positions along these two spectra, our results provide a basis to improve global vegetation models predicting responses of tropical forests to global change.
Ecology Letters

hal-01032142
https://hal.archives-ouvertes.fr/hal-01032142
DOI : 10.1111/j.1461-0248.2010.01517.x

Éditeur(s) : HAL CCSD Wiley
Résumé : International audience
1. A substantial fraction of the freshwater available in neotropical forests is impounded within the rosettes of bromeliads that form aquatic islands in a terrestrial matrix. The ecosystem functioning of bromeliads is known to be influenced by the composition of the contained community but it is not clear whether bromeliad food webs remain functionally similar against a background of variation in the understorey environment. 2. We considered a broad range of environmental conditions, including incident light and incoming litter, and quantified the distribution of a very wide range of freshwater organisms (from viruses to macroinvertebrates) to determine the factors that influence the functional structure of bromeliad food webs in samples taken from 171 tank-bromeliads. 3. We observed a gradient of detritus-based to algal-based food webs from the understorey to the overstorey. Algae, rotifers and collector and predatory invertebrates dominated bromeliad food webs in exposed areas, whereas filter-feeding insects had their highest densities in shaded forest areas. Viruses, bacteria and fungi showed no clear density patterns. Detritus decomposition is mainly due to microbial activity in understorey bromeliads where filter feeders are the main consumers of microbial and particulate organic matter (POM). Algal biomass may exceed bacterial biomass in sun-exposed bromeliads where amounts of detritus were lower but functional diversity was highest. 4. Our results provide evidence that tank-bromeliads, which grow in a broad range of ecological conditions, promote aquatic food web diversity in neotropical forests. Moreover, although bromeliad ecosystems have been categorised as detritus-based systems in the literature, we show that algal production can support a non-detrital food web in these systems.
ISSN: 0046-5070

hal-00819103
https://hal.archives-ouvertes.fr/hal-00819103

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : International audience
Gravitropism is necessary for plants to control the orientation of their axes while they grow in height. In woody plants, stem re-orientations are costly because they are achieved through diameter growth. The functional diversity of gravitropism was studied to check if the mechanisms involved and their efficiency may contribute to the differentiation of height growth strategies between forest tree species at the seedling stage. Seedlings of eight tropical species were grown tilted in a greenhouse, and their up-righting movement and diameter growth were measured during three months. Morphological, anatomical and biomechanical traits were measured at the end of the survey. Curvature analysis was used to analyse the up-righting response along the stems. Variations in stem curvature depend on diameter growth, size effects, the increase in self-weight, and the efficiency of the gravitropic reaction. A biomechanical model was used to separate these contributions. Results showed that (1) gravitropic movements were based on a common mechanism associated to similar dynamic patterns, (2) clear differences in efficiency (defined as the change in curvature achieved during an elementary diameter increment for a given stem diameter) existed between species, (3) the equilibrium angle of the stem and the anatomical characters associated to the efficiency of the reaction also differed between species, (4) the differences in gravitropic reaction were related to the light requirements: heliophilic species, compared to more shade-tolerant species, had a larger efficiency and an equilibrium angle closer to vertical. This suggests that traits determining the gravitropic reaction are related to the strategy of light interception and may contribute to the differentiation of ecological strategies promoting the maintenance of biodiversity in tropical rain forests.
ISSN: 0022-0957

hal-00797023
https://hal.archives-ouvertes.fr/hal-00797023
https://hal.archives-ouvertes.fr/hal-00797023/document
https://hal.archives-ouvertes.fr/hal-00797023/file/Functional_diversity_gravitropic_Almeras_al.pdf

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : The diversity and functional identity of organisms are known to be relevant to the maintenance of ecosystem processes but can be variable in different environments. Particularly, it is uncertain whether ecosystem processes are driven by complementary effects or by dominant groups of species. We investigated how community structure (i.e., the diversity and relative abundance of biological entities) explains the community-level contribution of Neotropical ant communities to different ecosystem processes in different environments. Ants were attracted with food resources representing six ant-mediated ecosystem processes in four environments: ground and vegetation strata in cropland and forest habitats. The exploitation frequencies of the baits were used to calculate the taxonomic and trophic structures of ant communities and their contribution to ecosystem processes considered individually or in combination (i.e., multifunctionality). We then investigated whether community structure variables could predict ecosystem processes and whether such relationships were affected by the environment. We found that forests presented a greater biodiversity and trophic complementarity and lower dominance than croplands, but this did not affect ecosystem processes. In contrast, trophic complementarity was greater on the ground than on vegetation and was followed by greater resource exploitation levels. Although ant participation in ecosystem processes can be predicted by means of trophic-based indices, we found that variations in community structure and performance in ecosystem processes were best explained by environment. We conclude that determining the extent to which the dominance and complementarity of communities affect ecosystem processes in different environments requires a better understanding of resource availability to different species.
ISSN: 0029-8549

hal-01606497
https://hal.archives-ouvertes.fr/hal-01606497
DOI : 10.1007/s00442-016-3741-z
PRODINRA : 407457

Résumé : Les termites ont un rôle clé dans le fonctionnement de l’écosystème forêt en particulier celui du recyclage de la litière en matière organique. Cependant, quelques espèces de termites sont des xylophages spécialisés dans la dégradation du bois des forêts, mais sont considérés comme des nuisibles dans les zones anthropisées.En France, le problème « termites » lié aux constructions n’a été traité que dans les années 90. La loi n°99-471, votée le 8 juin 1999 définit les modalités de mise en oeuvre d´une politique de lutte dans laquelle sont engagés tous les acteurs: l´Etat, les collectivités locales, les professionnels ainsi que les propriétaires d´immeubles. La Guyane-française est située dans la carte établie par le FCBA des départements de France où l’arrêté est effectif. Toutefois, ce département d’outre-mer reste aujourd’hui avec beaucoup de lacunes en termes de connaissances sur ses termites.On connaît de façon exhaustive le nombre et les différentes espèces de termites xylophages et on sait également quelles sont les principales familles qui sont présentes dans les bâtiments. Mais on ne sait pas dire quelles sont les espèces de termites qui s’intéressent à nos bois d’œuvres.L’objectif de cette étude est d’identifier les genres et espèces de termites qui s’attaquent à trois essences de bois de durabilité faible ou moyenne (Gonfolo, Simarouba et Yayamadou) et de comprendre comment ces attaques se produisent, en contexte forestier, en lien avec des variables du milieu, et l’effet de la saison de mise en contact.Le Yayamadou est une espèce très appétante pour les termites de Guyane, à condition de disposer de tas de bois d’un volume suffisant (> 500cm3), c’est l’espèce qui présente la plus grande diversité de termites actifs. 18 espèces de termites ont été trouvées sur les tas de bois, mais 10 seulement avec une fréquence dépassant le %. Une description détaillée et une clé d’identification sont proposées pour ces espèces.La diversité des termites est plus importante dans les milieux forestiers naturels. Les résultats montrent, qu’Heterotermes tenuis est l’espèce la plus fréquente quel que soit le milieu. Il y a une spécificité attractive de certaines espèces de termites pour telle essence plutôt que telle autre.Enfin, la saisonnalité, correspondant au moment où l’on installe les échantillons de bois en forêt, joue un rôle dans l’apparition de termites sur telle ou telle essence de bois. Il existe dans chaque milieu des espèces qui peuvent potentiellement s’attaquer au bois des habitations
The termites have a role key in the functioning of the ecosystem forest in particular the one of the recycling of the litter in organic matter. Nevertheless, some termites species are specialized in the degradation of the wood of the forests, but are considered plagues in humans place.In France, the problem « termites » linked by the buildings was treated only in the 90’s. The law n°99-471, voted by the 8 June 1999 defines the methods of implement of politics to fights in which are engaged all the actors: the government, the local groups, the professionals as well as the owners of buildings. The French Guiana-is in the map established by the FCBA that departments of France where the law is effective. Nevertheless, this “outre-mer” department remains today with a lot of gaps in terms of knowledge on its termites. We know in a manner exhaustive the number and the different types of xylophagous termites and we know too which are the principal families that are present in the buildings. But we don’t know to say which are the types of termites that are very interested in our lumber.The objective of this study is to identify the genera and termites species that attack themselves to three sorts of wood of weak or average durability (Gonfolo, Simarouba et Yayamadou) and to understand how these attacks produce themselves, in forest context, in link with variables of the environment, and the effect of the season of placement in contact.The Yayamadou is a Wood specie that atracts a lot of termites in French Guiana, to condition to have access to pile of wood of a sufficient volume (> 500cm3), it is the type that presents the biggest diversity of active termites. 18 species of termites were found on the wood piles, but 10 only with a frequency surpassing the 80%. A detailed description and an identification key are proposed for these species. The diversity of the termites is more important in the natural forest environments. The results show, that Heterotermes tenure is the type the does more frequent whatever the environment. There is an attractive specificity of some types of termites for such wood species rather than such other.Finally, the seasonality, corresponding the moment when we installs the wood samples in forest, plays a role in the appearance of termites on such or such wood species. There are in every environment of the types that potentially can attack the wood of the buildings.

http://www.theses.fr/2012AGUY0571/document

Éditeur(s) : HAL CCSD AGU and the Geochemical Society
Résumé : International audience
We propose a new thermomechanical numerical model of mid-ocean ridge accretion aimed at investigating asymmetric spreading rates, diverse configurations of lens and sill magma injections, crystallization and depth, and on- and off-axis patterns of hydrothermal cooling. The numerical algorithm iteratively resolves temperature and motion equations until it reaches a stationary solution. The motion equation was written in a vorticity-stream function formalism, with boundary and internal conditions applied to the stream function to impose the style of magma injection. Unlike in previous models, our model does not assume an a priori shape for the temperature field, which is initiated by an initial half-space cooling according to the left and right spreading rates. Complex patterns of hydrothermal cooling are simulated by enhanced thermal diffusivity. The model succeeds in describing the dynamic and thermal effects of spreading rates, the style of magma intrusion, and the hydrothermal cooling. Accurate descriptions of these are essential to study the cooling histories of crustal rocks and geophysical observables.
ISSN: 1525-2027

hal-00413118
https://hal.archives-ouvertes.fr/hal-00413118
DOI : 10.1029/2008GC002270

Éditeur(s) : HAL CCSD Kluwer Academic Publishers
Résumé : International audience
The interlocking leaves of tank-forming bromeliads (Bromeliaceae) collect rainwater and detritus, thus creating a freshwater habitat for specialized organisms. Their abundance and the possibility of quantifying communities with accuracy give us unparalleled insight into how changes in local to regional environments influence community diversity in small water bodies. We sampled 365 bromeliads (365 invertebrate communities) along a southeastern to northwestern range in French Guiana. Geographic locality determined the species pool for bromeliad invertebrates, and local environments determined the abundance patterns through the selection of traits that are best adapted to the bromeliad habitats. Patterns in community structure mostly emerged from patterns of predator species occurrence and abundance across local-regional environments, while the set of detritivores remained constant. Water volume had a strong positive correlation with invertebrate diversity, making it a biologically relevant measure of the pools' carrying capacity. The significant effects of incoming detritus and incident light show that changes in local environments (e.g., the conversion of forest to cropping systems) strongly influence freshwater communities. Because changes in local environments do not affect detritivores and predators equally, one may expect functional shifts as sets of invertebrates with particular traits are replaced or complemented by other sets with different traits.
Hydrobiologia

hal-00845572
https://hal.archives-ouvertes.fr/hal-00845572