Éditeur(s) : HAL CCSD Nature Publishing Group
Résumé : International audience
Tropical cyclone (TC) waves can severely damage coral reefs. Models that predict where to find such damage (the 'damage zone') enable reef managers to: 1) target management responses after major TCs in near-real time to promote recovery at severely damaged sites; and 2) identify spatial patterns in historic TC exposure to explain habitat condition trajectories. For damage models to meet these needs, they must be valid for TCs of varying intensity, circulation size and duration. Here, we map damage zones for 46 TCs that crossed Australia's Great Barrier Reef from 1985–2015 using three models – including one we develop which extends the capability of the others. We ground truth model performance with field data of wave damage from seven TCs of varying characteristics. The model we develop (4MW) out-performed the other models at capturing all incidences of known damage. The next best performing model (AHF) both under-predicted and over-predicted damage for TCs of various types. 4MW and AHF produce strikingly different spatial and temporal patterns of damage potential when used to reconstruct past TCs from 1985–2015. The 4MW model greatly enhances both of the main capabilities TC damage models provide to managers, and is useful wherever TCs and coral reefs co-occur.
ISSN: 2045-2322

Droits : http://creativecommons.org/licenses/by/
hal-01330362
https://hal-univ-perp.archives-ouvertes.fr/hal-01330362
https://hal-univ-perp.archives-ouvertes.fr/hal-01330362/document
https://hal-univ-perp.archives-ouvertes.fr/hal-01330362/file/srep26009.pdf
DOI : 10.1038/srep26009

Éditeur(s) : Elsevier
Résumé : The present work is based on a set of bottom trawl surveys performed in the Gulf of Lions between 1983 and 1992. A new method which couples the STATIS multitable approach with the logic of correspondence analysis (CoA) is proposed to study the stability of spatial organization of demersal assemblages in terms of species composition. This CoA version of STATIS has provided a clear representation of the stable part of the spatial structure of the assemblages. In addition, it gave an insight into the interannual variations of the distribution of each population around the reference structure. Our results showed that the demersal assemblages of the Gulf of Lions exhibited strong spatial structuring, mainly orientated along a bathymetric gradient. This gradient is structured around three major regions: the coast, the continental shelf and the continental slope. Despite sampling variations that occurred during the course of the study, the analysis showed a high degree of reproducibility for this spatial pattern. With the exception of Mullus surmuletus, the species considered in this investigation exhibit limited variations in their spatial distribution. Finally, in the absence of log-books covering the activities of commercial fishing vessels, these findings constitute a base of reference for the analysis of the dynamics of fishing fleets exploiting the demersal resources of the Gulf of Lions.
Ce travail porte sur une série de campagnes de chalutage de fond réalisé dans le golfe du Lion entre 1983 et 1992. Une nouvelle méthode fondée sur le couplage de la technique multitableaux STATIS et de l'analyse factorielle des correspondances (AFC) est proposée afin d'étudier l'organisation spatio-temporelle des assemblages démersaux, poissons et quelques céphalopodes, en terme de composition spécifique. Cette version AFC de STATIS a fourni une représentation claire de la part stable de l'organisation spatiale des assemblages. De plus, elle nous a permis d'appréhender les variations interannuelles de la distribution de chaque population autour de la structure de référence. Nos résultats montrent que les assemblages démersaux du golfe du Lion présentent une forte structuration spatiale, principalement orientée selon un gradient bathymétrique. Ce dernier est structuré en trois grandes régions: la côte, le plateau continental et le talus continental. En dépit des variations d'échantillonnage survenues au cours de la période d'étude, l'analyse a mis en évidence une forte reproductibilité de ce schéma d'organisation. A l'exception de Mullus surmuletus, les espèces considérées dans ce travail présentent des variations limitées de leur distribution spatiale. Enfin, en l'absence de livres de bord sur l'activité des navires professionnels, ces résultats constituent une base de référence pour l'analyse de la dynamique des flottilles exploitant les ressources démersales dans le golfe du Lion.
Aquatic Living Resources (Elsevier), 1998-03 , Vol. 11 , N. 2 , P. 75-85

Droits : 1998 Published by Elsevier SAS
http://archimer.ifremer.fr/doc/1998/publication-875.pdf
DOI:10.1016/S0990-7440(98)80063-6
http://archimer.ifremer.fr/doc/00000/875/

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 Public Library of Science
Résumé : International audience
Understanding how communities respond to natural disturbances is fundamental to assess the mechanisms of ecosystem resistance and resilience. However, ecosystem responses to natural disturbances are rarely monitored both through space and time, while the factors promoting ecosystem stability act at various temporal and spatial scales. Hence, assessing both the spatial and temporal variations in species composition is important to comprehensively explore the effects of natural disturbances. Here, we suggest a framework to better scrutinize the mechanisms underlying community responses to disturbances through both time and space. Our analytical approach is based on beta diversity decomposition into two components, replacement and biomass difference. We illustrate this approach using a 9-year monitoring of coral reef fish communities off Moorea Island (French Polynesia), which encompassed two severe natural disturbances: a crown-of-thorns starfish outbreak and a hurricane. These disturbances triggered a fast logistic decline in coral cover, which suffered a 90% decrease on all reefs. However, we found that the coral reef fish composition remained largely stable through time and space whereas compensatory changes in bio-mass among species were responsible for most of the temporal fluctuations, as outlined by the overall high contribution of the replacement component to total beta diversity. This suggests that, despite the severity of the two disturbances, fish communities exhibited high resistance and the ability to reorganize their compositions to maintain the same level of total community biomass as before the disturbances. We further investigated the spatial congruence of this pattern and showed that temporal dynamics involved different species across sites; yet, herbivores controlling the proliferation of algae that compete with coral communities were consistently favored. These results suggest that compensatory changes in bio-mass among species and spatial heterogeneity in species responses can provide further
ISSN: 1932-6203

hal-01212344
https://hal-univ-perp.archives-ouvertes.fr/hal-01212344
https://hal-univ-perp.archives-ouvertes.fr/hal-01212344/document
https://hal-univ-perp.archives-ouvertes.fr/hal-01212344/file/journal.pone.0138696.pdf
DOI : 10.1371/journal.pone.0138696

Éditeur(s) : HAL CCSD Nature Publishing Group
Résumé : Isozyme markers were used to characterize levels of diversity, genotypic structure and spatial genetic structure for the low-density tree species, Carapa procera (five adults per ha), within 300 ha of a continuous tropical rain forest stand. Both seed and adult stages were investigated, a high level of genetic diversity being found in both. Fixation indices showed excess homozygosity in seeds, and excess heterozygosity in adults, which might be caused by selection in favour of heterozygotes. Autocorrelation analysis of the spatial distribution of genotypes revealed no significant pattern in adults or in seeds before dispersal, and there was a high variability in correlogram shapes among alleles. This suggests that gene flow is extensive in C. procera, probably mainly through long-distance pollen dispersal, as seed dispersal is expected to be rather limited in this species (maximum distances of about 50 m). No clear-cut spatial pattern was observed in pollen allele frequencies, which supports the hypothesis of extensive pollen flow. This overall lack of structure is consistent with the data already available on the mating system of this predominantly outcroissing species.
ISSN: 0018-067X

hal-01032057
https://hal.archives-ouvertes.fr/hal-01032057
DOI : 10.1038/hdy.1997.124

Éditeur(s) : HAL CCSD Public Library of Science
Résumé : International audience
The effects of biodiversity on the transmission of infectious diseases now stand as a cornerstone of many public health policies. The upper Amazonia and Guyana shield are hot-spots of biodiversity that offer genuine opportunities to explore the relationship between the risk of transmission of Chagas disease and the diversity of its triatomine vectors. Over 730 triato-mines were light-trapped in four geomorphological landscapes shaping French-Guiana, and we determined their taxonomic status and infection by Trypanosoma cruzi. We used a model selection approach to unravel the spatial and temporal variations in species abundance , diversity and infection. The vector community in French-Guiana is typically made of one key species (Panstrongylus geniculatus) that is more abundant than three secondary species combined (Rhodnius pictipes, Panstrongylus lignarius and Eratyrus mucronatus), and four other species that complete the assemblage. Although the overall abundance of adult triatomines does not vary across French-Guiana, their diversity increases along a coastal-inland gradient. These variations unravelled a non-monotonic relationship between vector biodiversity and the risk of transmission of Chagas disease, so that intermediate biodiversity levels are associated with the lowest risks. We also observed biannual variations in triatomine abundance, representing the first report of a biannual pattern in the risk of Cha-gas disease transmission. Those variations were highly and negatively correlated with the average monthly rainfall. We discuss the implications of these patterns for the transmission of T. cruzi by assemblages of triatomine species, and for the dual challenge of controlling Amazonian vector communities that are made of both highly diverse and mostly intrusive species.
ISSN: 1935-2727

Droits : http://creativecommons.org/licenses/by/
hal-01298091
https://hal-univ-perp.archives-ouvertes.fr/hal-01298091
https://hal-univ-perp.archives-ouvertes.fr/hal-01298091/document
https://hal-univ-perp.archives-ouvertes.fr/hal-01298091/file/journal.pntd.0004427.PDF
DOI : 10.1371/journal.pntd.0004427

Éditeur(s) : HAL CCSD Elsevier
Résumé :  
The within-population spatial structure of genetic diversity is shaped by demographic processes, including historical accidents such as forest perturbations. Information drawn from the analysis of the spatial distribution of genetic diversity is therefore inherently linked to demographic-historical processes that ultimately determine the fate of populations. All adult trees and saplings in a 1.4-ha plot within a mixed Norway spruce (Picea abies [L.] Karst) stand were characterised by means of chloroplast (paternally inherited) markers, and a large sub-sample of these were genotyped at mitochondrial (maternally inherited) molecular markers. These data were used to analyse the spatial distribution of genetic variation and to compare the patterns corresponding to the two marker types. The plot presented non-homogeneous local stem density in the younger cohorts, and the indirect effect of this source of variation on the spatial genetic structure was investigated. Results suggest that (i) spatially limited seed dispersal induced patchiness in genotype distribution, while pollen flow had a homogenising effect; (ii) deviations from random spatial structure were stronger in the demographically most stable portions of the stand, while they were weaker where sudden bursts of regeneration occurred; (iii) spatially overlapping adult and sapling cohorts displayed the same spatial genetic structure (stronger on stable areas, weaker in portions of the stand undergoing events of intense regeneration), which was substantiated by the influence of local demographic processes. Regeneration dynamics as modulated by demography thus influences the distribution of genetic diversity within the stand both in the younger life stages and in the adult population.
ISSN: 0378-1127

hal-01032063
https://hal.archives-ouvertes.fr/hal-01032063
DOI : 10.1016/j.foreco.2008.03.023

Éditeur(s) : HAL CCSD Springer Verlag (Germany)
Résumé :  
We explored the relationship between soil processes, estimated through soil respiration (Rsoil), and the spatial variation in forest structure, assessed through the distribution of tree size, in order to understand the determinism of spatial variations in Rsoil in a tropical forest. The influence of tree size was examined using an index (Ic) calculated for each tree as a function of (1) the trunk cross section area and (2) the distance from the measurement point. We investigated the relationships between Ic and litterfall, root mass and Rsoil, respectively. Strong significant relationships were found between Ic and both litterfall and root mass. Rsoil showed a large range of variations over the 1-ha experimental plot, from 1.5 to 12.6 gC m−2 d−1. The best relationship between Ic and Rsoil only explained 17% of the spatial variation in Rsoil. These results support the assumption that local spatial patterns in litter production and root mass depend on tree distribution in tropical forests. Our study also emphasizes the modest contribution of tree size distribution-which is mainly influenced by the presence of the biggest trees (among the large range size of the inventoried trees greater than 10 cm diameter at 1.30 m above ground level or at 0.5 m above the buttresses)-in explaining spatial variations in Rsoil.
Plant and Soil

hal-01032200
https://hal.archives-ouvertes.fr/hal-01032200
DOI : 10.1007/s11104-011-0848-1

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
We explore the relations between deformation, annealing, and melt percolation during rifting and the effect of these processes on seismic anisotropy by analyzing the microstructures and crystal preferred orientations (CPO) in a suite of mantle xenoliths from Mega, in the southern end of the Ethiopian rift. Previous geochemical studies on these xenoliths showed evidence for interactions with variable melt types and volumes during the rifting process. The peridotites have dominantly coarse-porphyroclastic microstructures, but coarse granular or partially recrystallized microstructures also occur. The olivine CPO, characterized by orthorhombic to fiber-[100] patterns and moderate intensities, the common occurrence of (100) tilt walls, and the predominance of <0vw> rotation axes accommodating low angle misorientations in olivine support deformation by dislocation creep with dominant activation of the [100](010) system. Annealing (static recrystallization) of variable intensity followed this deformation. Modal enrichment in pyroxenes in > 60% of the studied peridotites corroborates extensive, but spatially heterogeneous reactive melt percolation leading to refertilization of the lithospheric mantle beneath the southern Ethiopian rift. The common interstitial shapes of the pyroxenes and lack of correlation between the pyroxenes and the olivine CPOs in many samples suggest that part of the refertilization is post-kinematic. However, there is no simple relation between reactive melt percolation and annealing of the olivine deformation microstructure. Comparison with data from other xenolith localities points to changes in the metasomatic imprint in the lithospheric mantle along the East African rift system correlated with the evolution in the rift maturity. Seismic properties averaged over all samples show typical lithospheric mantle patterns with fast propagation of P- and polarization of the fast S-waves parallel to the lineation. The anisotropy is moderate (< 6% for P-waves and < 4% for S-waves), implying that aligned melt must contribute to the strong seismic anisotropy measured in the Main Ethiopian rift, north of Mega.
ISSN: 0040-1951

hal-01355918
https://hal.archives-ouvertes.fr/hal-01355918
DOI : 10.1016/j.tecto.2016.05.027

Éditeur(s) : HAL CCSD Wiley-Blackwell
Résumé : International audience
The spatio‐temporal dynamics of disease spread provide an area of acute scientific interest but substantial analytic challenges. Analytic approaches need to draw from current knowledge of disease systems yet be flexible enough to provide targeted inference without restrictive assumptions. We explore this balance in detail with respect to the observed pattern of spread of sugarcane yellow leaf virus, the causal agent of yellow leaf disease. This disease affects cultivated sugarcane plants and spreads via an aphid vector (Melanaphis sacchari). The system is of considerable economic interest, but presents several analytic complications. First, the plants begin as well separated individuals that grow into large plants with overlapping leaf canopies enabling increased vector access between neighbouring plants. The overlap between neighbouring plants first occurs within rows and then extends between rows, presenting another interesting spatial component to consider when modelling the propagation of infection. Second, the vector initially flies between plants but at some point sheds wings and shifts to walking between plants. We are particularly interested in how these two features of the system and their interrelation may impact the spatial spread of disease over time. In addition, we also explore the impact of potential immigration of infected vectors from outside of the study area. We treat our observed cane field as a spatial grid with regular spacing between rows and smaller spacing within rows. Our data consist of observed disease status of each of 1643 plants at each of six time points. We provide descriptive summaries of the temporal evolution of spatial pattern in infection, then propose hierarchical models to describe the pattern and capture the influence of the ecological and environmental factors listed above.
ISSN: 0143-9782

hal-00684235
https://hal.archives-ouvertes.fr/hal-00684235

Éditeur(s) : HAL CCSD
Résumé : For a decade, distance-based methods have been largely employed and improved in the field of spatial economics. Such tools are very powerful to evaluate accurately the spatial distribution of plants or retail stores for example (Duranton and Overman, 2008; Jensen and Michel, 2011). In the present paper, we introduce a new statistic measure based on distances to evaluate the spatial concentration of economic activities. As far as we know, the m function is the first relative density function proposed in the economic literature. This tool completes the typology of distance-based methods recently drawn up by Marcon and Puech (2014). By working on several theoretical and empirical examples, we prove the advantages and the limits of the m function to gauge the spatial structures in spatial economics.
https://hal.archives-ouvertes.fr/hal-01082178

hal-01082178
https://hal.archives-ouvertes.fr/hal-01082178
https://hal.archives-ouvertes.fr/hal-01082178/document

Éditeur(s) : HAL CCSD Wiley
Résumé :  
Aims: Astrocaryum sciophilum (Miq.) Pulle (Arecaceae) is an understorey palm, endemic to north-eastern South America with a patchy distribution. We tested the hypothesis that the spatial distribution of this palm species is not in equilibrium but is slowly colonizing the forest understorey. Location: Inventories and seed dispersal studies were conducted in the undisturbed tropical forest close to the Nouragues research station, French Guiana. Additional data were collected in the entire territory of French Guiana. Methods: We studied the demography of A. sciophilum on a 20-ha plot located at the edge of its distribution. The age of the palms was estimated by postulating an exponentially decreasing abundance by age class. Direct seed dispersal experiments were also conducted, to estimate dispersal parameters. The seeds of A. sciophilum were dispersed only by rodents. This information was used to parameterize a forest growth simulator, to study the spatial spread of this species. Results: Within the sampling plot, the density of A. sciophilum dropped sharply from about 500 individuals per hectare to zero. The maturation age was estimated to be 170 ± 70 years, and over 55 years with 95% confidence. Seed-dispersal experiments yielded an average seed dispersal distance of 11 m and a maximum estimated dispersal distance of 125 m across a generational span of 55 years to maturity. Therefore, the maximal estimated colonization speed is 2.3 m/y. Conclusions: Empirical results and numerical simulations suggest that the boundary of the A. sciophilum population is a colonization front, and that the range of this species is slowly expanding. The implications of this result in respect of palaeoenvironmental changes in this region are discussed.
ISSN: 1466-822X

hal-01032154
https://hal.archives-ouvertes.fr/hal-01032154
DOI : 10.1046/j.1466-822X.2003.00020.x

Éditeur(s) : HAL CCSD
Résumé :  
The spatial genetic differentiation among European beech stands in western Germany was analysed by a new method. The genetic structure at 8 enzyme gene loci of 100 sampled populations was used as data base. The data represent authors' own results and published data from 8 different studies. For 10 geographic distance classes [h] from 0 to 500 km, the average genetic distance between the populations for each single gene locus, a gene-pool distance and the semivariances of genetic diversity gam were computed. Significant deviation from random spatial genetic structure was tested by permutation analysis. In many cases (Lap-B, Mdh-B, Mdh-C and 6Pgdh-C) the mean genetic distance between stands with spatial distance up to 200 km was significantly smaller and the genetic distance between stands with geographic distances of 200 and 400 km was significantly greater than expected for random spatial genetic structure. Similar tendencies were found for the gene-pool distance and the semivariances of diversity. Kriging, as a method for spatial interpolation, was used to draw synthetic maps of the spatial patterns of allelic frequencies and genetic diversity. The influence of postglacial recolonisation and regeneration with foreign seed material on the spatial genetic patterns are discussed
Forest genetics

hal-01032093
https://hal.archives-ouvertes.fr/hal-01032093

Éditeur(s) : HAL CCSD Elsevier
Résumé : Understanding the pattern in spatial distribution of soil microbial processes is critical to understand the environmental factors that regulate them as well as to scale up these processes to ecosystem. Soil samples from a I ha tropical rainforest plot (Paracou, French Guiana) were analyzed according a nested sampling approach using different separation distances ranging from 0.4 to 40 m. The variability of substrate induced respiration (SIR) and of denitrification enzyme activity (DEA) was characterized in relation to various soil properties (total C and N contents, NIRS related index of soil organic matter quality, SOMQ and index of tree influence potential, IP). The variability of SIR and DEA was higher than that of environmental properties. The patterns of accumulated variance as a function of distance varied among the soil properties. The variability of SIR and DEA mainly occurred at small (1 m) scale (and at the 10-40 m-scales for SIR), probably reflecting the quality of litter input that results of the influence of local assemblage of different tree species, though changes in the soil N and C contents. Indeed, total soil C and N contents explained the microbial properties at every scale. Coefficients of codispersion showed that neither SOMQ nor IP did correlate with SIR and DEA, and confirmed that total C and N contents explained microbial properties in a scale dependent and complex manner. Such spatial dependency underlines the importance of soil heterogeneity in this tropical forest with implications for sampling strategies when studying the microbial processes and their response to disturbances. (C) 2012 Elsevier B.V. All rights reserved.
ISSN: 0016-7061

hal-01032409
https://hal.archives-ouvertes.fr/hal-01032409
DOI : 10.1016/j.geoderma.2012.12.009

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The Kazdag Massif exposes an extensional metamorphic dome in the Biga Peninsula of northwest Turkey, bounded on both flanks by detachments and/or shear zones. The northern flank is marked by the extensional Alakeci shear zone (ASZ), with poorly known P-T-t path. We therefore focus on metamorphic conditions and temporal history of the ASZ to determine its tectono-metamorphic evolution. ASZ mylonites were derived from both the footwall Kazdag Massif core metamorphic rocks and the hanging wall Cetmi melange lithologies. The mylonitic fabrics in the ASZ depict a top-to-the NNE shearing, parallel to the NNE-plunging stretching lineation and NNW-dipping mylonitic foliation. This geometry implies normal sense movement i.e. north-side down-dip extensional displacement along this flank of the Kazdag Massif. The northward transition from ductile to brittle-ductile shear regime through the ASZ shows that the non-coaxial deformation occurred at decreasing temperatures and degree of metamorphism. The paragenesis in equilibrium of the mylonitic gneisses and schists contains quartz + feldspar + muscovite + biotite + garnet staurolite, with late retrogressive chlorite after biotite and garnet. Calculated thermo-barometric conditions for ASZ rocks yielded pressures between 6.9 and 5.7 kbar and temperatures between 706 and 587 degrees C, which constrain the peak metamorphism. The mylonitic rocks supplied isochron Ar-39/Ar-40 mica ages between 26.97 and 24.19 Ma, which we interpret to date the cooling of the mylonites following the P-T decrease across the ASZ. The metamorphic data support the structural record and strengthen the extensional character of the ASZ. The transition from sillimanite-bearing footwall Kazdag Massif core gneisses in the deeper structural levels to chlorite schists; towards the shallow structural levels at the top of the ASZ, is consistent with an extensional exhumation of the metamorphic pile. These data allow us to determine the peak P-T conditions and the temporal evolution in the northern flank of the Kazdag Massif, where Late Oligocene extensional exhumation was assisted by NNE-directed ductile-brittle ASZ, which had operated from amphibolite to greenschist facies. The ASZ, together with similar time-constrained ductile-brittle activity of SW-directed detachment along the southern flank of the massif, collectively indicates a bivergent mode of extension in the western Kazdag Massif. The latter is likely influenced by magmatic activity spatially and temporally related to these extensional zones. At the regional scale, the bivergent tectono-metamorphic pattern of the Kazdag Massif is similar to those observed on other places of the north-central Aegean domain.
ISSN: 0024-4937

hal-00445246
https://hal.archives-ouvertes.fr/hal-00445246
DOI : 10.1016/j.lithos.2009.02.010

Éditeur(s) : Amer Geophysical Union
Résumé : The temporal evolution and spatial distribution of surface salinity and colored detrital matter (cdm) were evaluated within and adjacent to the Amazon River Plume. Study objectives were as follows: first, to document the spatial coherence between Amazon discharge, salinity, cdm, and the nature of the salinity-cdm relationship; second, to document the temporal and spatial variability of cdm along the trajectory of the low-salinity Amazon Plume, and third, to explore the departure of cdm from conservative mixing behavior along the plume trajectory into the open ocean. Time series (2003-2007) of surface salinity estimated using the Advanced Microwave Scanning Radiometer-Earth Observing System and corresponding satellite cdm absorption (acdm) data documented a plume of freshened, colored water emanating from the Amazon. Salinity and acdm were generally coherent, but there were regions in which spatial patterns of salinity and acdm did not coincide. Salinity was oppositely phased with discharge, whereas acdm was in phase but lagged discharge and typically remained high after maximum discharge. Along the river plume trajectory, acdm was inversely correlated with salinity, yet there was considerable deviation from conservative mixing behavior during all seasons. Positive anomalies in a linear relationship between salinity and acdm corresponded to areas of enhanced satellite-retrieved net primary productivity, suggesting the importance of phytoplankton biomass or its subsequent remineralization as a source of cdm. Negative anomalies tended to predominate at the distal sections of the plume trajectories, an observation consistent with the process of photo-oxidation of cdm over observed time scales of days to weeks.
Journal Of Geophysical Research-oceans (0148-0227) (Amer Geophysical Union), 2011-07 , Vol. 116 , N. C00H02 , P. 14 p.

Droits : 2011 American Geophysical Union. All Rights Reserved.
http://archimer.ifremer.fr/doc/00041/15218/12593.pdf
DOI:10.1029/2011JC006989
http://archimer.ifremer.fr/doc/00041/15218/

Éditeur(s) : HAL CCSD
Résumé : Over the last decade, distance-based methods have been introduced and then improved in the field of spatial economics to gauge the geographic concentration of activities. There is a growing literature on this theme including new tools, discussions on their specific properties and various applications. However, there is currently no typology of distance-based methods. This paper fills that gap. The proposed classification helps understand all the properties of distance-based methods and proves that they are variations on the same framework.
https://halshs.archives-ouvertes.fr/halshs-00679993

halshs-00679993
https://halshs.archives-ouvertes.fr/halshs-00679993
https://halshs.archives-ouvertes.fr/halshs-00679993v6/document
https://halshs.archives-ouvertes.fr/halshs-00679993/file/MARCON-PUECH-Hal%2000679993v6.pdf

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 BioMed Central
Résumé : International audience
Background: Heterogeneous patterns of malaria transmission are thought to be driven by factors including host genetics, distance to mosquito breeding sites, housing construction, and socio-behavioural characteristics. Evaluation of local transmission epidemiology to characterize malaria risk is essential for planning malaria control and elimination programmes. The use of geographical information systems (GIS) techniques has been a major asset to this approach. To assess time and space distribution of malaria disease in Bandiagara, Mali, within a transmission season, data were used from an ongoing malaria incidence study that enrolled 300 participants aged under six years old ". Methods: Children's households were georeferenced using a handheld global position system. Clinical malaria was defined as a positive blood slide for Plasmodium falciparum asexual stages associated with at least one of the following signs: headache, body aches, fever, chills and weakness. Daily rainfall was measured at the local weather station. Landscape features of Bandiagara were obtained from satellite images and field survey. QGIS™ software was used to map malaria cases, affected and non-affected children, and the number of malaria episodes per child in each block of Bandiagara. Clusters of high or low risk were identified under SaTScan W software according to a Bernoulli model. Results: From June 2009 to May 2010, 296 clinical malaria cases were recorded. Though clearly temporally related to the rains, Plasmodium falciparum occurrence persisted late in the dry season. Two " hot spots " of malaria transmission also found, notably along the Yamé River, characterized by higher than expected numbers of malaria cases, and high numbers of clinical episodes per child. Conversely, the northeastern sector of the town had fewer cases despite its proximity to a large body of standing water which was mosquito habitat. Conclusion: These results confirm the existence of a marked spatial heterogeneity of malaria transmission in Bandiagara, providing support for implementation of targeted interventions. Background Malaria is one of the leading causes of morbidity and mortality in the world, with an estimated 3.3 billion people at risk of malaria [1]. The incidence of malaria worldwide is estimated to be 216 million cases per year, with 81% of these cases occurring in sub-Saharan Africa. Malaria kills approximately 655,000 people per year; 91% of deaths occur in sub-Saharan Africa [1], mostly in children under five years of age. In Mali, West Africa, malaria represents 36.5% of consultation motives in health center, it is a leading cause of morbidity and mortality children of less than five years of age and the first reason of anaemia in pregnant women [2]. Malaria transmission is seasonal. Malaria parasite transmission and clinical disease are characterized by important microgeographic variation, often between adjacent villages, households or families [3-8]. This local heterogeneity is driven by a variety of factors including human genetics [9,10], distance to potential breeding sites [11,12], housing construction
ISSN: 1475-2875

hal-01307672
https://hal-amu.archives-ouvertes.fr/hal-01307672
https://hal-amu.archives-ouvertes.fr/hal-01307672/document
https://hal-amu.archives-ouvertes.fr/hal-01307672/file/1475-2875-12-82.pdf
DOI : 10.1186/1476-072X-2-5

Éditeur(s) : HAL CCSD Wiley
Résumé : International audience
AimEcological connectivity is currently considered to be essential to enhance biodiversity conservation efforts and benefit adjacent areas. We evaluate the spatial structure of vulnerable marine benthic invertebrate populations based on connectivity to improve the placement of marine protected areas.LocationGulf of Lions, NW Mediterranean Sea.MethodsWe used a spatially explicit metapopulation model to explore how larval dispersal affects marine benthic invertebrate dynamics at local and regional scales. Minimum recruitment success (the proportion of larvae that settle in a site and survive between spawning and first reproduction, which is required to ensure species persistence) is proposed as a measure of vulnerability. Three contrasting simulations were constructed: closed versus connected populations, habitat loss versus recruitment failure disturbances and varying patterns of oceanographic connectivity. The rescue factor (the ratio of minimum recruitment success in connected and closed populations) quantified the decrease in vulnerability because of oceanographic connectivity.ResultsIn the Gulf of Lions, connectivity reduced population vulnerability by a rescue factor of 5.3. The minimum recruitment success for regional persistence decreased from 3% to 0.2% when species' life expectancies increased from 2 to 50 years. Connectivity enabled the spread of individuals over the entire region, but there were higher densities in sink sites, where low retention rates do not allow for local persistence (western tip of the gulf). Source sites, defined as those sites bringing metapopulation resistance to recruitment failure and stresses from habitat loss, were located in the centre of the gulf.Main conclusionsConnectivity drives the spatial structure of population density distribution and population vulnerability in the absence of any other structuring factor. In the Gulf of Lions, marine protected areas are located in population sinks; however; if protection measures were taken in the central part, populations would benefit throughout the region via the rescue effect.
ISSN: 1366-9516

hal-01341743
https://hal-univ-perp.archives-ouvertes.fr/hal-01341743
DOI : 10.1111/ddi.12254