Éditeur(s) : Université Bretagne Ouest
Résumé : This work deals with the fishing effects on the diversity dynamics of demersal fish communities, focusing on the biotic interactions. Multispecies indices are used in order to characterize the demersal fish community dynamics of the Bay of Biscay and of the Gulf of Lions. These are the diversity indices, the temporal variability of the total biomass and of the slope of the number size spectra and the slope of the species-area curves (spatial segregation). The yearly bottom trawl surveys EVHOE, CHALIST and MEDITS, carried out in these two areas since 1983 by IFREMER for the stocks assessment provide the data. The differences between areas are related to a fishing index (mean value of the annual landings of demersal fish per surface area). Other areas are included in the analysis when the index values are available from the published literature (North Sea, Scotian Shelf, Kenya, French Guyana). It is argued from the diversity indices analysis that the Gulf of Lions community is more diverse and less disturbed than the Bay of Biscay one. This result is not consistent with a fishing effect but with biogeography. The total biomass variability and the slope variability of size spectra are higher in the most harvested areas than in the least ones. On the contrary, the species-area slope is the lowest in the most harvested areas. Theoretically, biotic interactions decrease the total biomass variability and the spectra slope variability because of compensations and increase the species area slope because of competitive exclusion. It is concluded that harvesting alters biotic interactions and favour local coexistence by decreasing competitive exclusion. The species diversity maintenance depends on competitive exclusion. Hence, biodiversity is threatened not only by a direct fishing effect but also by a dynamics alteration.
Ce mémoire aborde le problème de l'impact de l'exploitation par la pêche sur la dynamique de diversité des peuplements de poissons démersaux. Les effets de la pêche sur le rôle des interactions biotiques entre espèces dans la dynamique des peuplements sont plus particulièrement analysés à l'aide de descripteurs multispécifiques. Les descripteurs utilisés sont les indices de diversité, la variabilité temporelle de la biomasse totale et de la pente multispécifique du spectre de poids et la pente des droites d'accumulation d'espèces mesurant la ségrégation spatiale. Les valeurs de ces indices sont calculées à partir des données de campagnes annuelles de chalutage de fond EVHOE, CHALIST et MEDITS, menées par l'IFREMER depuis 1983 pour l'évaluation des ressources halieutiques dans le golfe de Gascogne et dans le golfe du Lion. Les différences de caractéristiques de dynamique entre les deux peuplements révélées par ces descripteurs sont mises en relation avec un indice d'exploitation (valeur moyenne des débarquements annuels, divisée par la surface du plateau de la région concernée). D'autres régions ont été intégrées dans cette analyse lorsque les valeurs des indicateurs étaient disponibles dans la littérature (Mer du Nord, plateau de Nouvelle-Ecosse, Kenya et Guyane Française). Les indices de diversité utilisés permettent de mettre en évidence que le peuplement du golfe du Lion est plus diversifié et moins soumis à perturbations que celui du golfe de Gascogne. Ces caractéristiques semblent dues à l'histoire biogéographique de ces deux régions et non à un effet de la pêche. La variabilité de la biomasse totale et celle de la pente du spectre multispécifique augmentent depuis les régions les moins exploitées vers les plus exploitées. A l'inverse, la ségrégation spatiale diminue. En théorie, les interactions entre espèces diminuent la variabilité temporelle de la biomasse totale et de la pente du spectre multispécifique, à cause de compensations entre espèces, et augmentent la ségrégation spatiale par exclusion compétitive. L'interprétation donnée des résultats obtenus est ainsi une altération des interactions entre les espèces par l'exploitation. En prélevant de la biomasse, l'exploitation augmente la disponibilité des ressources pour les individus non pêchés. En conséquence, l'exclusion compétitive diminue et la coexistence locale des individus est facilitée. A long terme, la diversité est donc menacée, non seulement par raréfaction des espèces prélevées par l'exploitation mais aussi parce que les interactions sont altérées et que le maintien de la diversité en dépend pour partie.

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/2000/these-6670.pdf
http://archimer.ifremer.fr/doc/00000/6670/

Éditeur(s) : HAL CCSD BioMed Central
Résumé : International audience
BACKGROUND: Sampling design is a key issue when establishing species inventories and characterizing habitats within highly heterogeneous landscapes. Sampling efforts in such environments may be constrained and many field studies only rely on subjective and/or qualitative approaches to design collection strategy. The region of Cacao, in French Guiana, provides an excellent study site to understand the presence and abundance of Anopheles mosquitoes, their species dynamics and the transmission risk of malaria across various environments. We propose an objective methodology to define a stratified sampling design. Following thorough environmental characterization, a factorial analysis of mixed groups allows the data to be reduced and non-collinear principal components to be identified while balancing the influences of the different environmental factors. Such components defined new variables which could then be used in a robust k-means clustering procedure. Then, we identified five clusters that corresponded to our sampling strata and selected sampling sites in each stratum. RESULTS: We validated our method by comparing the species overlap of entomological collections from selected sites and the environmental similarities of the same sites. The Morisita index was significantly correlated (Pearson linear correlation) with environmental similarity based on i) the balanced environmental variable groups considered jointly (p = 0.001) and ii) land cover/use (p-value<0.001). The Jaccard index was significantly correlated with land cover/use-based environmental similarity (p-value = 0.001). CONCLUSIONS: The results validate our sampling approach. Land cover/use maps (based on high spatial resolution satellite images) were shown to be particularly useful when studying the presence, density and diversity of Anopheles mosquitoes at local scales and in very heterogeneous landscapes.
BMC Ecology

pasteur-00914104
https://hal-riip.archives-ouvertes.fr/pasteur-00914104
https://hal-riip.archives-ouvertes.fr/pasteur-00914104/document
DOI : 10.1186/1472-6785-13-45
PUBMED : 24289184

Éditeur(s) : Wiley-blackwell Publishing, Inc
Résumé : Recent theoretical and field studies conducted in both terrestrial and marine ecosystems have suggested that diversity could be a more complex and multi-component concept than previously thought. However, it is still poorly understood to what extent the information provided by the various indices is complementary with regard to diversity, and to what extent this complementarity is reproducible in different situations or at different scales of observation. In the present work, we have analysed the reproducibility of the empirical relationships between 11 diversity indices related to four major aspects (components) of species diversity (species richness, rarity, evenness and species taxonomy) in order to determine whether there is a general pattern of redundancy or complementarity in diversity measures that holds across years, areas and spatial scales. We have applied this approach to groundfish diversity through the analysis of 2404 trawl hauls collected during the first large-scale annual surveys carried out using a single sampling design throughout the northern Mediterranean Sea (ranging from 36.3 to 45.7 degrees N, and 5.3 degrees W to 28 degrees E). Whatever the years, areas and scales studied, we found a strong reproducibility in the number and the nature of the main complementary components of diversity. The whole set of diversity indices considered may be roughly split into 6 complementary groups of descriptors. This result highlights that, in contrast to what is still the usual practice, monitoring diversity should not be based on only one or two of the most widely used components, even at large scale. Finally, in a context where developing tools for monitoring diversity is considered as a high priority worldwide, the strong reproducibility of the relationships between diversity indices we observed offers a basis for discussion of the feasibility and relevance of proposing a general shortlist of indices for monitoring diversity at different management scales.
Ecography (0906-7590) (Wiley-blackwell Publishing, Inc), 2010-12 , Vol. 33 , N. 6 , P. 1123-1135

Droits : 2010 The Authors / Ecography
http://archimer.ifremer.fr/doc/00029/14064/11382.pdf
DOI:10.1111/j.1600-0587.2009.06259.x
http://archimer.ifremer.fr/doc/00029/14064/

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : Understanding the genetic mechanisms of speciation and basis of species differences is among the most important challenges in evolutionary biology. Two questions of particular interest are what roles divergent selection and chromosomal differentiation play in these processes. A number of recently proposed theories argue that chromosomal rearrangements can facilitate the development and maintenance of reproductive isolation and species differences by suppressing recombination within rearranged regions. Reduced recombination permits the accumulation of alleles contributing to isolation and adaptive differentiation and protects existing differences from the homogenizing effects of introgression between incipient species. Here, we examine patterns of genetic diversity and divergence in rearranged versus collinear regions in two widespread, extensively hybridizing sunflower species, Helianthus annuus and Helianthus petiolaris, using sequence data from 77 loci distributed throughout the genomes of the two species. We find weak evidence for increased genetic divergence near chromosomal break points but not within rearranged regions overall. We find no evidence for increased rates of adaptive divergence on rearranged chromosomes; in fact, collinear chromosomes show a far greater excess of fixed amino acid differences between the two species. A comparison with a third sunflower species indicates that much of the nonsynonymous divergence between H. annuus and H. petiolaris probably occurred during or soon after their formation. Our results suggest a limited role for chromosomal rearrangements in genetic divergence, but they do document substantial adaptive divergence and provide further evidence of how species integrity and genetic identity can be maintained at many loci in the face of extensive hybridization and gene flow.
ISSN: 0737-4038

hal-01032153
https://hal.archives-ouvertes.fr/hal-01032153
DOI : 10.1093/molbev/msp043

Éditeur(s) : HAL CCSD Cambridge University Press (CUP)
Résumé : International audience
We studied the monogenean communities of 34 species of butterflyfish from the tropical Indo-West Pacific, identifying 13 dactylogyrid species (including two species that are presently undescribed). Monogenean assemblages differed significantly between host species in terms of taxonomic structure, intensity and prevalence. Parasite richness ranged from 0 (Chaetodon lunulatus) to 11 (C. auriga, C. citrinellus and C. lunula). Host specificity varied between the dactylogyrids species, being found on 2-29 of the 34 chaetodontid species examined. Sympatric butterflyfish species were typically parasitized by different combinations of dactylogyrid species, suggesting the existence of complex host-parasite interactions. We identified six clusters of butterflyfish species based on the similarities of their dactylogyrid communities. Dactylogyrid richness and diversity were not related to host size, diet specialization, depth range or phylogeny of butterflyfish species. However, there was a weak positive correlation between monogenean richness and diversity and host geographical range. Most communities of dactylogyrids were dominated by Haliotrema aurigae and H. angelopterum, indicating the importance of the genus Haliotrema in shaping monogenean communities of butterflyfishes. This study casts light on the structure of the monogenean communities of butterflyfishes, suggesting that the diversity and complexity of community structures arises from a combination of host species-specific parameters.
ISSN: 0031-1820

hal-01380679
https://hal-univ-perp.archives-ouvertes.fr/hal-01380679
DOI : 10.1017/S0031182016001463

Éditeur(s) : HAL CCSD Royal Society, The
Résumé : There is broad consensus that the diversity of functional traits within species assemblages drives several ecological processes. It is also widely recognized that rare species are the first to become extinct following human-induced disturbances. Surprisingly, however, the functional importance of rare species is still poorly understood, particularly in tropical species-rich assemblages where the majority of species are rare, and the rate of species extinction can be high. Here, we investigated the consequences of local and regional extinctions on the functional structure of species assemblages. We used three extensive datasets (stream fish from the Brazilian Amazon, rainforest trees from French Guiana, and birds from the Australian Wet Tropics) and built an integrative measure of species rarity versus commonness, combining local abundance, geographical range, and habitat breadth. Using different scenarios of species loss, we found a disproportionate impact of rare species extinction for the three groups, with significant reductions in levels of functional richness, specialization, and originality of assemblages, which may severely undermine the integrity of ecological processes. The whole breadth of functional abilities within species assemblages, which is disproportionately supported by rare species, is certainly critical in maintaining ecosystems particularly under the ongoing rapid environmental transitions.
ISSN: 0962-8452

hal-01532639
https://hal.archives-ouvertes.fr/hal-01532639
DOI : 10.1098/rspb.2016.0084
PRODINRA : 384617

Éditeur(s) : Inter-research
Résumé : Ecosystem-based management (EBM) requires more extensive information than single-species management. Active underwater acoustic methods provide a means of collecting a wealth of ecosystem information with high space-time resolution. Worldwide fisheries institutes and agencies are carrying out regular acoustic surveys covering many marine shelf ecosystems, but these data are underutilized. In addition, more and more acoustic data collected by vessels of opportunity are becoming available. To encourage their use for EBM, we provide a brief introduction to acoustic and complementary data collection methods in the water column, and review current and potential contributions to monitoring population abundance and biomass, spatial distributions, and predator-prey relationships. Further development of acoustics-derived indicators is needed. We review and propose indicators for assessing and monitoring zooplankton, population dynamics of fish and other nekton, and changes in diversity and food-web functioning. Acoustic methods have the potential to make a strong contribution to EBM. Evaluation of new indicators and suitable reference points in different ecosystems are the current challenges.
Marine Ecology-progress Series (0171-8630) (Inter-research), 2011 , Vol. 442 , P. 285-301

Droits : 2011 Inter-research
http://archimer.ifremer.fr/doc/00073/18445/15972.pdf
DOI:10.3354/meps09425
http://archimer.ifremer.fr/doc/00073/18445/

Éditeur(s) : HAL CCSD Ecological Society of America
Résumé : Line transect surveys are widely used in neotropical rainforests to estimate the population abundance of medium- and large-sized vertebrates. The use of indices such as Encounter Rate has been criticized because the probability of animal detection may fluctuate due to the heterogeneity of environmental conditions among sites. In addition, the morphological and behavioral characteristics (biological traits) of species affect their detectability. In this study, we compared the extent to which environmental conditions and species' biological traits bias abundance estimates in terra firme rainforests in French Guiana. The selected environmental conditions included both physical conditions and forest structure covariates, while the selected biological traits included the morphological and behavioral characteristics of species. We used the distance sampling method to model the detection probability as an explicit function of environmental conditions and biological traits and implemented a model selection process to determine the relative importance of each group of covariates. Biological traits contributed to the variability of animal detectability more than environmental conditions, which had only a marginal effect. Detectability was best for large animals with uniform or disruptive markings that live in groups in the canopy top. Detectability was worst for small, solitary, terrestrial animals with mottled markings. In the terra firme rainforests which represent ~80% of the Amazonia and Guianas regions, our findings support the use of relative indices such as the encounter rate to compare population abundance between sites in species-specific studies. Even though terra firme rainforests may appear similar between regions of Amazonia and the Guianas, comparability must be ensured, especially in forests disturbed by human activity. The detection probability can be used as an indicator of species' vulnerability to hunting and, thus, to the risk of local extinction. Only a few biological trait covariates are required to correctly estimate the detectability of the majority of medium- and large-sized vertebrates. Thus, a biological trait model could be useful in predicting the detection probabilities of rare, uncommon or localized species for which few data are available to fit the detection function.
ISSN: 1051-0761

hal-01555267
https://hal.archives-ouvertes.fr/hal-01555267
DOI : 10.1002/eap.1549
PRODINRA : 396614
PUBMED : 28419598

Éditeur(s) : Elsevier
Résumé : The multi-component aspect of species diversity of groundfish assemblages was examined on the basis of a set of experimental trawl surveys conducted on the east coast of Corsica. We analysed and compared the structuration of diversity within three different bathymetric strata: the continental shelf (60-120 m depth), the upper slope (250-400 m) and the lower slope (450-570 m). For each of these three bathymetric strata, we simultaneously analysed 12 indices that are theoretically complementary and relate to 4 diversity components: (1) the number of species, (2) rarity, (3) evenness and (4) taxonomic diversity. Principal component analysis based on Spearman's correlation coefficients was carried out to investigate empirical relationships between the selected indices. Our results showed not only that a single diversity index cannot provide a complete view of the groundfish diversity along the east coast of Corsica, but also that-in some cases-one index cannot even encapsulate a complete description of a specific diversity component. We also found that the nature and the number of independent diversity components slightly varied from one bathymetric stratum to another. The main differences-which mainly occurred in the deepest bathymetric stratum-might be associated with lower density of individuals and lower dominance of some species at deeper depths. Finally, this study is the first dealing with groundfish diversity in this area, which is currently characterized by one of the lowest fishing intensity rates in the northern Mediterranean Sea. It might be considered as a first '' reference state '' with a view to monitoring the spatio-temporal changes in species diversity patterns along the east coast of Corsica in the future. (C) 2007 Elsevier B.V. All rights reserved.
Fisheries Research (0165-7836) (Elsevier), 2007-12 , Vol. 88 , N. 1-3 , P. 120-132

Droits : 2007 Elsevier B.V. All rights reserved.
http://archimer.ifremer.fr/doc/2007/publication-3512.pdf
DOI:10.1016/j.fishres.2007.08.003
http://archimer.ifremer.fr/doc/00000/3512/

Éditeur(s) : HAL CCSD Inter-Research
Résumé : International audience
The effects of global change are particularly serious in areas where range shiftsof species are physically constrained such as the Ligurian Sea, which is one ofthe coldest sectors of the Mediterranean. In this basin, historical informationon water temperature (from the sea surface down to 75 m depth) dates backto the 1950s. Early studies also recorded warm-water species occurrence.Thanks to these data we provide the first detailed characterization of watertemperature variation from 1958 up to 2010 in the layer 0–75 m depth. Wecoupled this analysis with the available information on rocky reef epibenthiccommunities (literature review from 1955 to 1964 and field data from 1980 to2010). The analysis of water temperature revealed several patterns of variation:a cooling phase from 1958 to 1980, a phase of rapid warming from 1980 to1990 and a phase of slower warming from 1990 to 2010. Inter-annual variationin temperature increased over the entire period for the water layer down to20 m. Warm-water native and alien species richness increased during thewarming phases. Literature estimates suggest a decrease in warm-water nativespecies richness during the cooling phase. The analysis of quantitative data collectedin the early 1990s and late 2000s indicated a decrease in the cover ofwarm-water native species on shallow rocky reefs and an increase in deeperwaters. We argue that increased inter-annual variation in water temperaturemay disadvantage native warm-water species in shallow waters. Our resultsindicate that the effect of temperature rises in cold, constrained basins may bemore complex than the simple prediction of species changing their geographicalrange according to their thermal limits.
Marine Ecology Progress Series

hal-01239259
https://hal-univ-perp.archives-ouvertes.fr/hal-01239259
DOI : 10.1111/maec.12277

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : Functional aspects of biodiversity were investigated in a lowland tropical rainforest in French Guyana (5°2'N, annual precipitation 2200 mm). We assessed leaf '15N as a presumptive indicator of symbiotic N2 fixation, and leaf and wood cellulose '13C as an indicator of leaf intrinsic water-use efficiency (CO2 assimilation rate/leaf conductance for water vapour) in dominant trees of 21 species selected for their representativeness in the forest cover, their ecological strategy (pioneers or late successional stage species, shade tolerance) or their potential ability for N2 fixation. Similar measurements were made in trees of native species growing in a nearby plantation after severe perturbation (clear cutting, mechanical soil disturbance). Bulk soil '15N was spatially quite uniform in the forest (range 3-5‰), whereas average leaf '15N ranged from m0.3‰ to 3.5‰ in the different species. Three species only, Diplotropis purpurea, Recordoxylon speciosum (Fabaceae), and Sclerolobium melinonii (Caesalpiniaceae), had root bacterial nodules, which was also associated with leaf N concentrations higher than 20 mg gm1. Although nodulated trees displayed significantly lower leaf '15N values than non-nodulated trees, leaf '15N did not prove a straightforward indicator of symbiotic fixation, since there was a clear overlap of '15N values for nodulated and non-nodulated species at the lower end of the '15N range. Perturbation did not markedly affect the difference '15Nsoil m '15Nleaf, and thus the isotopic data provide no evidence of an alteration in the different N acquisition patterns. Extremely large interspecific differences in sunlit leaf '13C were observed in the forest (average values from m31.4 to m26.7‰), corresponding to intrinsic water-use efficiencies (ratio CO2 assimilation rate/leaf conductance for water vapour) varying over a threefold range. Wood cellulose '13C was positively related to total leaf '13C, the former values being 2-3‰ higher than the latter ones. Leaf '13C was not related to leaf '15N at either intraspecific or interspecific levels. '13C of sunlit leaves was highest in shade hemitolerant emergent species and was lower in heliophilic, but also in shade-tolerant species. For a given species, leaf '13C did not differ between the pristine forest and the disturbed plantation conditions. Our results are not in accord with the concept of existence of functional types of species characterized by common suites of traits underlying niche differentiation; rather, they support the hypothesis that each trait leads to a separate grouping of species.
ISSN: 0029-8549

hal-01032378
https://hal.archives-ouvertes.fr/hal-01032378
DOI : 10.1007/s004420050593

Éditeur(s) : HAL CCSD National Shellfisheries Association
Résumé : International audience
Monitoring gonad maturation for protandrous and functional hermaphrodite species such as the giant clam Tridacna maxima is difficult due to the juxtaposition and relative proportion of male and female tissues in the gonad [gonadal sex ratio (GSR)]. Here, the relevance of the widely used gonadosomatic index (GSI) as proxy of giant clam gonad maturation is tested with a large dataset (n ¼ 265). Gonadosomatic index is compared with other indices, namely the proportion of the male part harboring spermatozoids, the proportion of empty oocyte follicles, the mean oocyte diameter, and the oocyte elongation. At gonad scale, high index variability highlighted partial spawning. At individual scale, male and female maturation proxies were contrasted, showing either asynchronous emissions of male and female gametes or contrasted spermatogenesis and oogenesis duration. The GSI was mostly driven by the number and diameter of oocytes and therefore it is recommended here as primary proxy for female maturity. Except for the oocyte elongation, all indices were affected by the GSR, which ruled out drawing conclusions at population scale. These results highlight the need for maturation stage proxies that are optimized for functional hermaphrodite species.
ISSN: 0730-8000

hal-01613648
https://hal.archives-ouvertes.fr/hal-01613648
https://hal.archives-ouvertes.fr/hal-01613648/document
https://hal.archives-ouvertes.fr/hal-01613648/file/Gaertner-Mazouni-2016-eio.pdf
DOI : 10.2983/035.035.0107

Éditeur(s) : HAL CCSD Public Library of Science
Résumé : International audience
We assessed the occurrence of algae in five species of tank-bromeliads found in contrasting environmental sites in a Neotropical, primary rainforest around the Nouragues Research Station, French Guiana. The distributions of both algal abundance and biomass were examined based on physical parameters, the morphological characteristics of bromeliad species and with regard to the structure of other aquatic microbial communities held in the tanks. Algae were retrieved in all of the bromeliad species with mean densities ranging from ∼10(2) to 10(4) cells/mL. Their biomass was positively correlated to light exposure and bacterial biomass. Algae represented a tiny component of the detrital food web in shaded bromeliads but accounted for up to 30 percent of the living microbial carbon in the tanks of Catopsis berteroniana, located in a highly exposed area. Thus, while nutrient supplies are believed to originate from wind-borne particles and trapped insects (i.e., allochtonous organic matter), our results indicate that primary producers (i.e., autochtonous organic matter) are present in this insectivorous bromeliad. Using a 24-h incubation of size-fractionated and manipulated samples from this plant, we evaluated the impact of mosquito foraging on algae, other microorganisms and rotifers. The prey assemblages were greatly altered by the predation of mosquito larvae. Grazing losses indicated that the dominant algal taxon, Bumilleriopsis sp., like protozoa and rotifers, is a significant part of the diet of mosquito larvae. We conclude that algae are a relevant functional community of the aquatic food web in C. berteroniana and might form the basis of a complementary non-detrital food web.
ISSN: 1932-6203

hal-00819161
https://hal.archives-ouvertes.fr/hal-00819161
https://hal.archives-ouvertes.fr/hal-00819161/document
https://hal.archives-ouvertes.fr/hal-00819161/file/Brouard2011_AreAlgae.pdf
DOI : 10.1371/journal.pone.0020129

Résumé : Au cours de 325 relevés, 518 observations visuelles et 202 acoustiques ont permis de recenser 4 familles, 14 genres et 17 espèces, représentant un effectif total cumulé de près de 6000 cétacés contactés dans les limites de 15 mille nautiques des côtes en Guadeloupe. Les dauphins (Delphinidëe), constituent 33% des 36 espèces actuellement connues dans le monde. Six espèces plus rares ont été décrites. Parmi les cétacés à fanons, la baleine à bosse (Megaptera novaeangliae) migre dans les eaux côtières de décembre à fin mai et reste l'espèce la plus rencontrée. Grâce à un suivi individuel par télémétrie, il a pu être prouvé qu'au moins un individu de cette espèce pouvait séjourner dans l'archipel plus de huit jours. En 2010, une baleine à bosse de la baie du Moule à été suivie sur plus de 6300 kilomètres jusqu'au sud de l'Islande, vers les Iles Féroé. Une première estimation de stock sur la période de 2008 à 2011 propose que 442 baleines à bosse %CV 19,29 IC95% [302-645] évolueraient dans l'archipel côtier. Les carnïvores sont les plus abondants, avec parmi ceux-ci, le dauphin tacheté pantroplcal (Stenella attenuata) dont l'estimation indique que 270 à 300 individus évolueraient sur 1361 km2 avec une densité relative élevée (0,052 tndtvtdus/km>, %CV 90,16), principalement en-côte-sous-le-vent. L'analyse de la répartition spatiale et des facteurs du milieu indique une sectorisation géographique marquée des populations en zone côtière, avec des distributions influencées spécifiquement par la bathymétrie, la latitude, les distances à la côte et à l'isobathe 200, pour les informations principales et selon les espèces.
In 325 surveys, 518 visuai observations and acoustic 202 have identified four families, 14 genera and 17 species, representing a cumulative total ofnearly 6000 cetaceans assessed within 15 miles of coastal water ofGuadeloupe. Dolphins (Delphinidae), constitute 33% ofthe 36 species currently known in the world. Six rare species have been described. Among the baleen whales, the humpback whale (Megaptera novaeangliae) migrate into coastal waters from December to late May and is the species most encountered. With individual monitoring by telemetry, it has been proved that at least one individual ofthis species could stay in the archipelago over eight days. In 2010, a humpback whale in the Bay ofmold were followed for more than 6300 km to the south ofIceland to the Faroe Islands. A first estimate ofstock over the period 2008 to 20 Il suggests that 442 humpback whales CV% 19.2995% [302-645] would evolve in the coastal archipelago. <..';:-.'") Carnivores are the most abundant, with among them, the spotted dolphin (Stenella attenuata) whose estimate indicates that 270 to 300 individuals are present over 1361 km 2 with a high specifie density (0.052 individuals / km 2,% CV 90, 16), mainly in the Leeward coast. The analysis ofthe spatial distribution and environmental factors indicates a marked geographical sectorisation ofpopulations in coastal areas, with distributions specifically influenced by bathymetry, latitude, distance to the coast and the isobath 200, depending on the species

http://www.theses.fr/2012AGUY0520/document

Éditeur(s) : Pergamon-elsevier Science Ltd
Résumé : Epinephelus itajara is one of the marine fish species most threatened for extinction and it is considered to be "critically endangered" by the IUCN. The present study evaluated the genetic diversity of the species and the genetic/evolutionary relationships of its populations along the Atlantic coast of South America. The results indicate relatively reduced genetic variation, re-emphasizing the low adaptive potential of the species. One of the populations presented relatively high degrees of genetic diversity and it is evolutionary isolated from the all other populations. The evidences indicate the existence of two Evolutionarily Significant Units comprising E. itajara in the Atlantic coast of South America and the conservation prospects for the species must take these evidences into account.
Biochemical Systematics And Ecology (0305-1978) (Pergamon-elsevier Science Ltd), 2014-10 , Vol. 56 , P. 255-266

Droits : 2014 Elsevier Ltd. All rights reserved.
http://archimer.ifremer.fr/doc/00230/34100/34465.pdf
DOI:10.1016/j.bse.2014.06.004
http://archimer.ifremer.fr/doc/00230/34100/

Éditeur(s) : HAL CCSD Public Library of Science
Résumé : International audience
We conducted a survey along three belt transects located at increasing distances from the coast to determine whether a non-random arboreal ant assemblage, such as an ant mosaic, exists in the rainforest on the Masoala Peninsula, Madagascar. In most tropical rainforests, very populous colonies of territorially dominant arboreal ant species defend absolute territories distributed in a mosaic pattern. Among the 29 ant species recorded, only nine had colonies large enough to be considered potentially territorially dominant; the remaining species had smaller colonies and were considered non-dominant. Nevertheless, the null-model analyses used to examine the spatial structure of their assemblages did not reveal the existence of an ant mosaic. Inland, up to 44% of the trees were devoid of dominant arboreal ants, something not reported in other studies. While two Crematogaster species were not associated with one another, Brachymyrmex cordemoyi was positively associated with Technomyrmex albipes, which is considered an invasive species-a non-indigenous species that has an adverse ecological effect on the habitats it invades. The latter two species and Crematogaster ranavalonae were mutually exclusive. On the other hand, all of the trees in the coastal transect and at least 4 km of coast were occupied by T. albipes, and were interconnected by columns of workers. Technomyrmex albipes workers collected from different trees did not attack each other during confrontation tests, indicating that this species has formed a supercolony along the coast. Yet interspecific aggressiveness did occur between T. albipes and Crematogaster ranavalonae, a native species which is likely territorially dominant based on our intraspecific confrontation tests. These results suggest that the Masoala rainforest is threatened by a potential invasion by T. albipes, and that the penetration of this species further inland might be facilitated by the low density of native, territorially dominant arboreal ants normally able to limit its progression.
ISSN: 1932-6203

hal-00817444
https://hal.archives-ouvertes.fr/hal-00817444
https://hal.archives-ouvertes.fr/hal-00817444/document
https://hal.archives-ouvertes.fr/hal-00817444/file/Dejean2010_Spatial.pdf
DOI : 10.1371/journal.pone.0009319

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
We performed torsional deformation experiments on pre-hydrated fine-grained olivine aggregates using an innovative experimental assembly to investigate water weakening in mantle rocks at high shear strains. San Carlos olivine powder was cold-pressed and then hot-pressed under hydrous conditions, producing aggregates with average grain sizes of 7 or 15 μm. Deformation experiments were performed in a high-resolution gas-medium apparatus equipped with a torsional actuator, under a confining pressure of 300 MPa, a temperature of 1200 °C, and constant shear strain rates ranging from 8 × 10−5 to 1.4 × 10−4 s−1. Maximum shear stresses range from 150 to 195 MPa. These values are 30% lower relative to those determined in previous torsion experiments on dry, fined-grained dunites under similar conditions. Textures and microstructures of the starting and deformed specimens were characterized by scanning and transmission electron microscopy. All deformed aggregates exhibit a shape-preferred orientation marking a foliation and lineation, as well as a reduction in mean grain size from 15 μm down to 3-4 μm due to dynamic recrystallization. Olivine crystallographic fabrics developed rapidly (γ < 0.1), but their strength, characterized by the J-index, is low compared to naturally deformed peridotites or to polycrystalline olivine deformed at similar finite shear strains under dry conditions. The crystallographic fabrics are consistent with deformation by a dislocation accommodated creep mechanism with activation of multiple {0 k l}[1 0 0] systems, among which the (0 1 0)[1 0 0] slip system is dominant, and minor participation of the (0 1 0)[0 0 1] slip system. Transmission electron microscopy confirmed the occurrence of dislocations with [1 0 0] and [0 0 1] Burgers vectors in most grains. Analysis of unpolarized infrared spectra indicates that hydrogen concentration in the olivine lattice is below the saturation level of 18 ppm wt H2O, which is similar to those typically observed in spinel-bearing peridotite xenoliths, and also provide evidence for water-rich inter-granular material trapped in pores and grain boundaries. Seismic properties computed from the CPO observations correspond to those most commonly observed in naturally deformed mantle peridotites with fast P-wave propagation and S-wave polarization subparallel to the shear direction. These torsion experiments on fine-grained olivine polycrystals under hydrous conditions indicate that water weakening under lithospheric conditions is linked to various defects with hydrogen in the olivine structure, as well as with water-derived species in grain boundaries or pores.
ISSN: 0031-9201

hal-00745170
https://hal.archives-ouvertes.fr/hal-00745170
DOI : 10.1016/j.pepi.2012.05.001

Éditeur(s) : HAL CCSD
Résumé : International audience
Radiocarbon dating and "old wood problem" in the Antilles : the state of the artAmong the many effects that may distort the interpretation of radiocarbon dates are those for which the age of the archaeological event is different from the radiocarbon age of the sample or "14C event" age. This type of problem arises in many cases, notably in the "old wood effect”, and occurs in various regions of the world where very long-lived trees species are common. In the Caribbean anthracological studies indicate a very high frequency of some indigenous centuries-old species such as Guaiacum, Guaiacum officinale L. However the absence of tree-ring data in humid tropical zones deprives us of an accurate inventory of long-lived species and especially the assessment of their longevity. Here we present measurements which enable us to estimate the longevity of archaeological Guaiacum wood posts. They highlight a gap of several centuries between wood from the outer edge and the heart of the tree. This example illustrates the additional uncertainty that can result from dating archeological events when dates are realized on unidentified botanical species from which the area that was sampled is unknown. Another source of error could arise from the use of rot-proof dead wood as fuel if we take into consideration that major hurricanes can produce large amounts of dead wood that may be collected for decades, even centuries. To improve chronometric data used in archaeological interpretations, it is necessary to ensure the quality of the dating process by following a protocol similar to those used in other regions of the world based on a better understanding of the material to be dated by preliminary identifications of wood samples: species, anatomical part, wood moisture content (unseasoned or seasoned).
Radiocarbono y "problema madera vieja", que data de las Antillas: estado del arteEntre los muchos efectos que pueden distorsionar la interpretación de fechas de radiocarbono, destacan aquellos para los que la edad de la prueba arqueológica es diferente de la edad de radiocarbono de la muestra, o la edad del "evento de radiocarbono." Este tipo de problema se presenta en muchos casos, especialmente uno llamado "efecto madera vieja." Esto se refleja en diversas regiones del mundo donde las especies de plantas de mucha longevidad son comunes. En el Caribe, los estudios antracológicos disponibles indican una muy alta frecuencia de algunas especies autóctonas como el guayaco, Guaiacum officinale L. Sin embargo, la casi ausencia de datos de anillos de árboles en los trópicos húmedos, nos impide realizar un inventario exacto de especies de mucha longevidad y sobre todo la evaluación de la longevidad. Algunas de las pruebas presentadas aquí permitieron una estimación de la longevidad de de unos postes de guayaco de origen arqueológico. Ponen de manifiesto una brecha de varios siglos entre las partes externas y el corazón del tronco. Este ejemplo ilustra la aparición de una incertidumbre adicional en la datación de los eventos arqueológicos cuando no conocemos la especie botánica y tampoco la zona de la muestra en el árbol. Otra fuente de error puede surgir de la utilización de la madera muerta de calidad duradera como combustible ya que los grandes huracanes pueden producir grandes cantidades de madera muerta, que puede ser requerida durante décadas, incluso siglos. Para mejorar los datos cronométricos utilizados en interpretaciones arqueológicas, es necesario asegurarse de la calidad de las fechas, y por lo tanto seguir un protocolo similar a los utilizados en otras regiones fundado en una mejor comprensión de los elementos: especie, parte anatómica, humedad de la madera usada (verde o seco).
Parmi les nombreux effets susceptibles de fausser l’interprétation des datations par le radiocarbone, figurent ceux pour lesquels l’âge de l’événement archéologique est différent de l’âge radiocarbone de l’échantillon, ou âge de l’« événement radiocarbone ». Ce type de problème se pose dans de nombreux cas, en particulier celui dénommé « effet vieux bois ». Cette question est prise en compte dans diverses régions du monde où des espèces végétales très longévives sont fréquentes. Dans les Antilles les études anthracologiques disponibles indiquent une fréquence très importante de certaines espèces autochtones multiséculaires dont le gaïac, Guaiacum officinale L.. Cependant, la quasi absence de données dendrochronologiques dans la zone tropicale humide, nous privent d’un inventaire précis des espèces longévives et surtout de l’évaluation de leur longévité. Quelques tests présentés ici ont permis une estimation de la longévité de poteaux d’origine archéologique en bois de gaïac. Ils mettent en évidence un décalage de plusieurs siècles entre les parties externes et le cœur du tronc. Cet exemple illustre l’apparition d’une incertitude supplémentaire dans la datation de l’événement archéologique lorsque que l’on ne connaît ni l’espèce botanique ni la zone de prélèvement dans l’arbre. Une autre source d’erreur pourrait provenir de l’utilisation de bois mort de qualité très durable comme combustible, sachant que les grands cyclones peuvent produire d’importantes quantités de bois mort susceptible d’être récolté pendant des décennies, voire des siècles. Afin d’améliorer les données chronologiques utilisées dans les interprétations archéologiques, il apparaît nécessaire de s’assurer de la qualité des datations, et donc de suivre un protocole similaire à ceux utilisés dans d’autres régions basé sur une meilleure connaissance des éléments datés : espèce, partie anatomique, humidité du bois utilisé (vert ou sec).
Puerto Rico 2013 : Actas del 25to Congreso Internacional de Arqueología del Caribe - Proceeding of the 25th International Congress for Caribbean Archeology - Comptes rendus des communications du 25e Congrés International de l'Archéologie de la Caraïbe
San-Juan, Puerto Rico

hal-01198567
https://hal.archives-ouvertes.fr/hal-01198567
https://hal.archives-ouvertes.fr/hal-01198567/document
https://hal.archives-ouvertes.fr/hal-01198567/file/Stouvenot%20et%20al.%202015.%20Effet%20vieux%20bois%20radiocarbone%20Antilles%20HD.pdf

Éditeur(s) : Soc Francaise D Ichtyologie
Résumé : This work deals with the fishing effects on the diversity dynamics of demersal fish communities, focusing on the biotic interactions. Multispecies indices were used in order to characterise the demersal fish community dynamics of the Bay of Biscay and of the Gulf of Lions. These are the diversity indices, the temporal variability of the total biomass and of the slope of the number size spectra and the slope of the species-area curves (spatial segregation). The data were provided by yearly bottom trawl surveys EVHOE, CHALIST and MEDITS carried out in these two areas since 1983 by IFREMER for stock assessment. The differences between areas are related to a fishing index (mean value of the annual landings of demersal fish per surface area). Other areas are included in the analysis when the index values are available from the published literature (North Sea, Scotian Shelf, Kenya, French Guyana). From the diversity indices analysis it is argued that the Gulf of Lions community is more diverse and less disturbed than the Bay of Biscay one. This result is not consistent with a fishing effect. It is interpreted as a biogeography pattern. The total biomass variability and the slope variability of size spectra are higher in the most harvested areas than in the least ones. On the contrary, the species-area slope is the lowest in the most harvested areas. Theoretically, biotic interactions decrease the total biomass variability and the spectra slope variability because of compensations, and increase the species area slope because of competitive exclusion. It is concluded that harvesting alters biotic interactions and favours local coexistence by decreasing competitive exclusion. The species diversity maintenance depends on competitive exclusion. Hence, biodiversity is threatened not only by a direct fishing effect but also by a dynamics alteration.
Ce mémoire aborde le problème de l'impact de l'exploitation par la pêche sur la dynamique de diversité des peuplements de poissons démersaux. Les effets de la pêche sur le rôle des interactions biotiques entre espèces dans la dynamique des peuplements sont plus particulièrement analysés à l'aide de descripteurs multispécifiques. Les descripteurs utilisés sont les indices de diversité, la variabilité temporelle de la biomasse totale et de la pente multispécifique du spectre de poids et la pente des droites d'accumulation d'espèces mesurant la ségrégation spatiale. Les valeurs de ces indices sont calculées à partir des données de campagnes annuelles de chalutage de fond EVHOE, CHALIST et MEDITS, menées par l'IFREMER depuis 1983 pour évaluer les ressources halieutiques dans le golfe de Gascogne et dans le golfe du Lion. Les différences de caractéristiques de dynamique entre les deux peuplements révélées par ces descripteurs sont mises en relation avec un indice d'exploitation (valeur moyenne des débarquements annuels, divisée par la surface du plateau de la région concernée). D'autres régions ont été intégrées dans cette analyse lorsque les valeurs des indicateurs étaient disponibles dans la littérature (Mer du Nord, plateau de Nouvelle-Ecosse, Kenya et Guyane Française). Les indices de diversité utilisés permettent de mettre en évidence que le peuplement du golfe du Lion est plus diversifié et moins soumis à perturbations que celui du golfe de Gascogne. Ces caractéristiques semblent dues à l'histoire biogéographique de ces deux régions et non à un effet de la pêche. La variabilité de la biomasse totale et celle de la pente du spectre multispécifique augmentent depuis les régions les moins exploitées vers les plus exploitées. A l'inverse, la ségrégation spatiale diminue. En théorie, les interactions entre espèces diminuent la variabilité temporelle de la biomasse totale et de la pente du spectre multispécifique, à cause de compensations entre espèces, et augmentent la ségrégation spatiale par exclusion compétitive. L'interprétation donnée des résultats obtenus est ainsi une altération des interactions entre les espèces par l'exploitation. En prélevant de la biomasse, l'exploitation augmente la disponibilité des ressources pour les individus non pêchés. En conséquence, l'exclusion compétitive diminue et la coexistence locale des individus est facilitée. A long terme, la diversité est donc menacée, non seulement par raréfaction des espèces prélevées par l'exploitation mais aussi parce que les interactions sont altérées et que le maintien de la diversité en dépend pour partie.
Cybium (0399-0974) (Soc Francaise D Ichtyologie), 2001 , Vol. 25 , N. 3 , P. 293-294

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/00000/10248/7688.pdf
http://archimer.ifremer.fr/doc/00000/10248/

Éditeur(s) : HAL CCSD European Geosciences Union (EGU)
Résumé : International audience
Pollen and clay mineralogical analyses of a Holocene sequence from Sebkha Boujmel (southern Tunisia) traces the climatic and environmental dynamics in the lower arid bioclimatic zone over the last 8000 years. During the Mid- to Late Holocene transition, between 8 and 3 ka, a succession of five wet/dry oscillations is recorded. An intense arid event occurs between 5.7 and 4.6 ka. This episode marks the onset of a long-term aridification trend with a progressive retreat of Mediterranean woody xerophytic vegetation and of grass steppes. It ends with the establishment of pre-desert ecosystems around 3 ka. The millennial-scale climate change recorded in the data from Sebkha Boujmel is consistent with records from the south and east Mediterranean, as well as with climatic records from the desert region for the end of the African Humid Period (AHP). Eight centennial climatic events are recorded at Sebkha Boujmel and these are contemporary with those recorded in the Mediterranean and in the Sahara. They indicate a clear coupling between the southern Mediterranean and the Sahara before 3 ka. The event at 4.2 ka is not evidenced and the link between events recorded in Sebkha Boujmel and the North Atlantic Cooling events is clearer from 3 ka onwards. These variations indicate the importance of climatic determinism in the structuring of landscapes, with the establishment of the arid climatic conditions of the Late Holocene. It is only from 3 ka onwards that the dynamic of plant associations is modified by both human activity and climatic variability. The climatic episodes identified during the historic period indicate strong regionalisation related to the differential impact of the North Atlantic Oscillation (NAO) and the Mediterranean Oscillation (MO) on the Mediterranean basin. The local human impact on regional ecosystems is recorded in the form of episodes of intensification of pastoral and/or agricultural activities. The development of olive production and of several taxa associated with agriculture attest to increasing sedentism among human populations during Classical Antiquity. The significant increase in Artemisia (wormwood) between 1.1 and 0.8 ka (850–1150 AD) is linked to intensive pastoral activity, associated with heightened interannual and/or seasonal climatic instability. A complete re-shaping of the landscape is recorded during the 20th century. The remarkable expansion of the olive tree, and the deterioration of regional ecosystems with the spread of desert species, is linked to recent local socio-economic changes in Tunisia.
ISSN: 1814-9324

hal-01319967
https://hal.archives-ouvertes.fr/hal-01319967
https://hal.archives-ouvertes.fr/hal-01319967/document
https://hal.archives-ouvertes.fr/hal-01319967/file/cp-12-1339-2016.pdf
DOI : 10.5194/cp-12-1339-2016