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National audience; This research aims to evaluate the relevance of using the diversity measurements on satellite images taking into account the problem of the MAUP (Modifiable Areal Unit Problem). We calculate a vegetation indice for an image SPOT 5 of 5 meters resolution. Then, we cut out the image into grids of different aggregated resolution. For each image, we calculate 3 diversity index: Shannon, Simpson and Dominance. We process a resampling of the observed data and design another image corresponding to the "maximal" diversity. Same calculations of diversity index are applied on these two images. We then measure the extent and the evolution of the phenomenon through the scales according to the types of images and the statistical distributions of the pixels. The results show how sensitive is the diversity assessment to the MAUP and how we may identify what we call a "pertinent scale"; Cette recherche vise à évaluer la pertinence de l'utilisation des mesures de diversité sur des images satellitaires en abordant le problème du MAUP (Modifiable Areal Unit Problem). Nous calculons tout d'abord un indice de végétation sur une image SPOT 5 de 5 mètres de résolution (image 1). Puis, nous créons une image répartissant aléatoirement ces mêmes pixels observés sur une zone de même taille (image 2). Deux images extrêmes sont également utilisées pour comparaison : une image de la diversité nulle (tous les pixels ont la même valeur, image 0) et une image de diversité « maximale » (tous les pixels sont différents, image 3). Nous découpons alors les images 1 et 2 en grilles de différentes résolutions, croissantes et imbriquées. Considérant les pixels de l'image initiale contenus dans chaque maille, nous calculons 3 indices de diversité, Shannon, Simpson et de Dominance. Les résultats présentés sont les moyennes, médianes et distributions statistiques des valeurs de diversité des mailles de chaque image. Ils permettent de mesurer l'ampleur et l'évolution de la sensibilité de ces indices à travers les échelles et selon les types d'images. Nous comparons aussi les écarts et les rapports entre les valeurs des diversités des trois séries. Les résultats permettent d'introduire et de discuter le concept d' « échelle pertinente »

Analyses of tree diversity and community composition in tropical rain forests are usually based either on general herbarium data or on a restricted number of botanical plots. Despite their high taxonomic accuracy, both types of data are difficult to extrapolate to landscape scales. Meanwhile, forestry surveys provide quantitative occurrence data on large areas, and are thus increasingly used for landscape-scale analyses of tree diversity. However, the reliability of these approaches has been challenged because of the ambiguity of the common (vernacular) names used by foresters and the complexity of tree taxonomy in those hyper-diverse communities. We developed and tested a novel approach to evaluate taxonomic reliability of forestry surveys and to propagate the resulting uncertainty in the estimates of several diversity indicators (alpha and beta entropy, Fisher-alpha and Sørensen similarity). Our approach is based on Monte-Carlo processes that simulate communities by taking into account the expected accuracy and reliability of common names. We tested this method in French Guiana, on 9 one-hectare plots (4279 trees – DBH ⩾ 10 cm) for which both common names and standardized taxonomic determinations were available. We then applied our method of community simulation on large forestry inventories (560 ha) at the landscape scale and compared the diversity indices obtained for 10 sites with those computed from precise botanical determination situated at the same localities. We found that taxonomic reliability of forestry inventories varied from 22% (species level) to 83% (family level) in this Amazonian region. Indices computed directly with raw forestry data resulted in incorrect values, except for Gini–Simpson beta-diversity. On the contrary, our correction method provides more accurate diversity estimates, highly correlated with botanical measurements, for almost all diversity indices at both regional and local scales. We obtained a robust ranking of sites consistent with those shown by botanical inventories. These results show that (i) forestry inventories represent a significant part of taxonomic information, (ii) the relative diversity of regional sites can be successfully ranked using forestry inventory data using our method and (iii) forestry inventories can valuably contribute to the detection of large-scale diversity patterns when biases are well-controlled and corrected. The tools we developed as R-functions are available in supplementary material and can be adapted with local parameters to be used for forest management and conservation issues in other regional contexts.

ResumeUne analyse retrospective des preferences trophiques de Glossina palpalis palpalis, vecteur majeur de la Trypanosomiase humaine africaine (THA) a ete faite a partir des donnees recueillies entre 1984 et 1994 dans cinq foyers du secteur forestier, dans le centre-ouest de la Cote d'Ivoire. Les auteurs ont compare le regime alimentaire de ce vecteur dans ces differents foyers. L'objectif est de verifier s'il existe une relation entre les preferences trophiques du vecteur et la prevalence de la THA. La diversite du regime alimentaire a eteevaluee par deux indices: l'indice de diversite de Shannon et Weaver (Ish) et un nouvel indice defini par le rapport pourcentage de repas de sang animal/pourcentage de repas de sang humain ou indice de zoophilie/ anthropophilie (Za). Il n'y a pas de correlation entre la DAP et le taux de prevalence. Des indices (Ish et Za) eleves, signe d'une diversite alimentaire, ont ete observes dans les foyers de Vavoua, Zoukougbeu et Sinfra ou les taux de prevalence de la THA etaient importants. Inversement des indices faibles ont ete notes dans les zones de faible prevalence comme Daniafla et Gagnoa ou la quasi totalite des repas de sang du vecteur etait pris sur l'hote humain. Il existe une correlation forte mais non significative entre les deux indices entomologiques et la prevalence de la maladie. La correlation est plus forte avec l'indice Za qu'avec l'indice Ish. La signification epidemiologique de ces observations est discutee. Summary The feeding habits of Glossina palpalis palpalis, the main vector of human African trypanosomiasis (HAT) were retrospectively analysed using data collected between 1984 and 1994 in five areas in the forest belt in the mid-west of Cote d'Ivoire. The authors compare the feeding habits of the vector in these different foci. This analysis is aimed at determining if there is any relationship between the feeding pattern of tsetse-flies and the prevalence rates of HAT. The feeding pattern was measured using two indices: the conventional index of Shannon and Weaver (Ish) and a new one, the zoophily/anthropophily index (Za). The latter is an estimate of the ratio of the percentage of animal blood meals divided by the percentage of human blood meals. There was no correlation between apparent density and prevalence rate. A high Ish and a high Za were observed in the foci of Vavoua, Zoukougbeu and Sinfra where prevalence rates of HAT were high. Conversely, a low Ish and a low Za were observed in the hypoendemic areas of Daniafla and Gagnoa. Both indices are highly but not significantly correlated with prevalence rates. The Za index seemed to be more strongly correlated to the disease rate as compared to the Ish index. The epidemiological significance of these observations is discussed.

Large-scale studies focused on the diversity of continental slope ecosystems are still rare, usually restricted to a limited number of diversity indices and mainly based on the empirical comparison of heterogeneous local data sets. In contrast, we investigate large-scale fish diversity on the basis of multiple diversity indices and using 1454 standardized trawl hauls collected throughout the upper and middle slope of the whole northern Mediterranean Sea (36 degrees 3' - 45 degrees 7' N; 5 degrees 3'W - 28 degrees E). We have analyzed (1) the empirical relationships between a set of 11 diversity indices in order to assess their degree of complementarity/redundancy and (2) the consistency of spatial patterns exhibited by each of the complementary groups of indices. Regarding species richness, our results contrasted both the traditional view based on the hump-shaped theory for bathymetric pattern and the commonly-admitted hypothesis of a large-scale decreasing trend correlated with a similar gradient of primary production in the Mediterranean Sea. More generally, we found that the components of slope fish diversity we analyzed did not always show a consistent pattern of distribution according either to depth or to spatial areas, suggesting that they are not driven by the same factors. These results, which stress the need to extend the number of indices traditionally considered in diversity monitoring networks, could provide a basis for rethinking not only the methodological approach used in monitoring systems, but also the definition of priority zones for protection. Finally, our results call into question the feasibility of properly investigating large-scale diversity patterns using a widespread approach in ecology, which is based on the compilation of pre-existing heterogeneous and disparate data sets, in particular when focusing on indices that are very sensitive to sampling design standardization, such as species richness.

*INRA C.R.Tours UR86 BASE 37380 Nouzilly Diffusion du document : INRA C.R.Tours UR86 BASE 37380 Nouzilly Diplôme : Dr. d'Université

On présente ici une approche pluri-spécifique, visant à évaluer les principales ressources démersales exploitées au Sénégal. En l'absence de statistiques d'effort de pêche fiables, deux séries d'efforts de pêche théoriques sont estimées à partir des données d'indices d'abondance disponibles (1971-1991). Ces deux séries se rapportent à des hypothèses différentes concernant l'évolution des puissances de pêche des flotilles ; elles sont respectivement qualifiées d'optimiste et de pessimiste. Pour chaque espèce ou taxon considéré, un modèle global est ajusté aux données de capture et d'effort. Un diagnostic est complété par le calcul d'indices de diversité des captures à l'équilibre, exprimés en fonction de l'effort de pêche. Au-delà des incertitudes de cette première évaluation, on montre que les ressources démersales sénégalaises sont dans une situation variant, selon les hypothèses retenues, de la pleine exploitation à une très nette surexploitation. Dans l'hypothèse pessimiste, 9 des 11 espèces ou groupes d'espèces de poissons étudiés seraient nettement surexploités, avec des efforts de pêche parfois double, voire triple de l'effort de "maximisation". La situation serait particulièrmenet dégradée pour #Arius$ sp. (mâchoiron), #Epinephelus aenus$ (thiof), #Papellus bellottii$ (pageot) et #Pomadasys$ sp. (sompatt). Pour les 11 espèces de poissons considérées, le diagnostic pluri-spécifique indique, dans cette hypothèse pessimiste, un effort presque double de l'effort de "maximisation", avec une Production Equilibrée Maximale estimée à environ 53 000 tonnes. A l'inverse, en 1991, la seiche et le poulpe seraient sous-exploités. On montre également que l'accroissement de l'effort se traduirait par une nette diminution de la diversité des prises. Ce résultat est interprété comme un signe de fragilité de l'écosystème exploité. (Résumé d'auteur)

National audience

National audience

The evolution of a plankton copepod population in the Mauritania upwelling was studied by following a drogue for 9 days, from the point of upwelling till the water-mass dives under offshore waters. The Shannon index of specific diversity and the tropic structure allow separation into several stages in the studied succession. The upwelling brings near the shore a rather poor, highly diverse fauna, with a low filter-feeder rate. The phytoplanktonic development induces an increase in the copepod number. The filter-feeders become dominant and the diversity decreases. When the increase of copepod number stops, the diversity decreases and the omnivore and carnivore rate increases.

Several 'analyses factorielles des correspondences' were used with the numerical data of planktonic copepods issued from a 1 year sampling programme at different stations of the Ivorian shelf. The main results were the following: (1) 'Ecological seasons' approximately corresponding to hydrological seasons may be defined for planktonic populations. (2) Each 'season' is characterized by one group of species, whose maximum abundance occurs in this period. (3) The same definition of ecological season is obtained whether all species present are used or whether only the most important ones are used. (4) The first principal axes may be interpreted as temperature and salinity or as the station's distance from shore.