Structure des communautés de plantes herbacées sur les Grands Causses : Stratégies fonctionnelles des espèces et interactions interspécifiques

Doctoral thesis (2008)

Plant community response to grazing management was studied on the INRA La Fage experimental station, Larzac Causse. Land use practices were considered as a disturbance and resource filter that remove ... [more ▼]

Plant community response to grazing management was studied on the INRA La Fage experimental station, Larzac Causse. Land use practices were considered as a disturbance and resource filter that remove species. The integrated approach of community structure used in this study was centred on plant functional traits. Continuous variations of plant traits associated with resource acquisition and early phenology indicated the replacement of stress tolerant species by ruderals along the gradient of land use intensity (grazing avoidance). Graminoids were particularly abundant in these communities. Changes in species identity and species functional identity were consistent with the grazing tolerance strategy. At the community scale, the strong functional convergence among dominant species confirmed the filtering effect of grazing management on these traits. Species richness reached its maximum at intermediate grazing. Maximal richness was associated with the coexistence of many growth forms and an important functional richness. These results are interpreted as an extension of the intermediate disturbance hypothesis to the traits of coexisting species. Finally, plant interaction dynamics experienced by five target species allowed us to identify the tendency of facilitated survival and intensely depressed biomass. The effect of communities was roughly similar although huge differences in specific and functional structure. The response to the least from competition and benefited the most from facilitation. [less ▲]

Structure des parois de Bacillus megaterium KM I. Isolement de l'amidase et d'un enzyme nouveau sécrétés par Streptomyces albus G et actifs sur les parois de Bacillus megaterium KM et de Micrococcus lysodeikticus

in Biochimica et Biophysica Acta (1962), 63(2), 286-296

The Streptomyces albus G enzymic complex of the F2B preparation has been fractionated by zone electrophoresis in sucrose gradient. Five enzymes have been shown to be present and three of them have been ... [more ▼]

The Streptomyces albus G enzymic complex of the F2B preparation has been fractionated by zone electrophoresis in sucrose gradient. Five enzymes have been shown to be present and three of them have been fully separated. Three distinct enzymes make the casein no further precipitable by the trichloroacetic acid. They are likely not to have any action on Bacillus megaterium KM and on Micrococcus lysodeikticus cell walls. A fourth enzyme is the amidase previously studied which splits the muraminyl-alanine linkages present in the bacterial walls. The amidase does not clarify by itself the wall suspensions so far examined but enhances the lytic activity of a fifth enzyme also present in the F2B preparation. As lysozyme and Streptomyces N-acetylhexosaminidase, this fifth enzyme seems to act at the level of the polysaccharide residues of the walls basal mucopeptide but, contrary to those enzymes, its hydrolyzing action does not induce the liberation of free oligosaccharides from Micrococcus lysodeikticus walls. This enzyme will be referred to as Enzyme “32”. [less ▲]

Structure des populations de renard roux, Vulpes vulpes, dans le sud de la Belgique en relation avec l'enzootie rabique et les campagnes de vaccination orale

in Cahiers d'Ethologie (1993), 13(3), 281-294

From 1989 to 1991, 549 fox carcasses were examined in oder to assess the impact of rabies control measures (oral vaccination with VVTGgRAB recombinant vaccinia-rabies virus). Their age was determined ... [more ▼]

From 1989 to 1991, 549 fox carcasses were examined in oder to assess the impact of rabies control measures (oral vaccination with VVTGgRAB recombinant vaccinia-rabies virus). Their age was determined using a lower canine tooth. The distinction between young and adults was made on radiographs, measuring the relative importance of the pulp cavity. Adult animals were aged by counting the annual growth cementum layers in tooth sections. The sex-ratio is in favour of the males and the age-pyramid is a large-base flattened one, with more than 60% of young (< 1 year) animals. Life expectancy at birth is 1.14 y. in the males and 1.23 y. in the females. The population turnover is quite high, the whole population being revewed in a 3-4 y. time interval. As far as the age structure is concerned, no difference has been found between males and females, rabid and sound animals, immunised or not. However, the spring vaccination campaign is much less efficient for the young foxes. These results suggest that rabies affects indistinctly all age classes of both sexes, just as it is the case with the autumn vacciation campaigns. Moreover, a comparison between the samples of two natural regions differing in their hunting system (big vs. small game) revealed no age structure difference suggesting that the high hunting pressure can explain better than rabies itself the very important juvenile prportion in the population. Nevertheless, some further research is needed to confirm that last point. [less ▲]

Structure detection in the D1 CFHTLS deep field using accurate photometric redshifts: a benchmark

in Astronomy and Astrophysics (2007), 467(1), 49-62

Aims. We investigate structures in the D1 CFHTLS deep field to test the method that will be applied to generate homogeneous samples of clusters and groups of galaxies in order to constrain the cosmology ... [more ▼]

Aims. We investigate structures in the D1 CFHTLS deep field to test the method that will be applied to generate homogeneous samples of clusters and groups of galaxies in order to constrain the cosmology and detailed physics of groups and clusters. Methods. An adaptive kernel technique was applied to galaxy catalogues. This technique needs none of the usual a-priori assumptions ( luminosity function, density profile, colour of galaxies) made with other methods. Its main drawback ( decrease in efficiency with increasing background) is overcome by the use of narrow slices in photometric redshift space. There are two main concerns in structure detection. One is false detection and the second, the evaluation of the selection function in particular if one wants complete samples. We deal with the first concern using random distributions. For the second, comparison with detailed simulations is foreseen but we used a pragmatic approach by comparing our results to GalICS simulations to check that our detection number is not totally at odds with cosmological simulations. We used the XMM-LSS survey and secured VVDS redshifts up to z similar to 1 to check individual detections. Results. We show that our detection method is basically able to recover 100% of the C1 XMM-LSS X-ray detections ( in the regions in common) in the correct redshift range plus several other candidates. Moreover, when spectroscopic data are available, we confirm our detections, even those without X-ray data. [less ▲]

Structure du (Méthyl-1-pipérazinyl-4)-5 Pyrido[2,3-b][1,5]benzothiazépine

in Acta Crystallographica Section C-Crystal Structure Communications (1988), C44

Structure du 8-chloro-11-(méthylpipérazin-1-yl)dibenzo[b,f]-1,4-thiazépine

in Acta Crystallographica Section C-Crystal Structure Communications (1992), C48

Structure du bromure de carboxyméthyl-3 thiazolium

in Acta Crystallographica (1989), C45

Structure du méthyl-4 pipérazinyl-1)-10 pyrido[4,3-b][1,4]benzothiazépine

in Acta Crystallographica Section C-Crystal Structure Communications (1991), C47

Structure du N-diméthylaminoéthyl Méthoxy-4 Pyridinesulfonamide-3 et du N-[(éthyl-1pyrrolidinyl-2) méthyl] Pyridinesulfonamide-3

in Acta Crystallographica Section C-Crystal Structure Communications (1990), C46

Structure et dynamique temporelle des communautés de crustacés amphipodes associés aux herbiers à Posidonia oceanica de la baie de Calvi

Master of advanced studies dissertation (2007)

L’objectif principal de ce travail était l’étude de la structure de la communauté d’amphipodes associés à la canopée des herbiers à Posidonia oceanica de la baie de Calvi, et de la dynamique saisonnière ... [more ▼]

L’objectif principal de ce travail était l’étude de la structure de la communauté d’amphipodes associés à la canopée des herbiers à Posidonia oceanica de la baie de Calvi, et de la dynamique saisonnière et nycthémérale de cette communauté. Il apparaît que la communauté étudiée est assez complexe. Elle est très riche en individus comme en espèces, et montre dans l’ensemble une diversité importante. De plus, les assemblages sont toujours dominés par quelques espèces très abondantes. Nous ne sommes pas parvenus à dégager de tendances claires quant à la variation saisonnière de la communauté étudiée. Néanmoins, seuls les prélèvements de deux saisons (novembre et mars) ont été traités dans le cadre de ce mémoire. Il est vraisemblable que la situation soit plus claire lors de l’examen des prélèvements d’une année entière. La variation nycthémérale, par contre, est très marquée. Les assemblages faunistiques sont beaucoup plus riches en individus et en espèces durant la nuit. De plus, nos résultats semblent indiquer que les amphipodes séjournent majoritairement dans la couche de litière à l’"interface" entre la matte et la strate foliaire durant la journée, alors qu’ils se déplaceraient activement au sein de la strate foliaire la nuit. Cette migration nycthémérale pourrait être une réponse à la prédation diurne par les poissons et/ou un moyen de maximiser l’exploitation des ressources trophiques offertes par l’herbier. Le second objectif de ce travail était de standardiser une méthode de prélèvement simple à mettre en œuvre, mais efficace et si possible quantitative. A cet effet, nous avons comparé trois méthodes, à savoir le filet fauchoir, le ramassage manuel de la litière et les pièges à lumière. Chaque méthode présente des avantages et des inconvénients. De plus, Les résultats obtenus via les trois méthodes ne convergent pas totalement. La communauté étudiée étant complexe, il est possible que ces divergences proviennent du fait que chacune d’entre elles ne permet de voir qu’une facette partielle d’un assemblage plus grand. Dans le but d’échantillonner aussi efficacement que possible l’ensemble de la communauté étudiée, il apparaît donc opportun de continuer à appliquer de front ces 3 méthodes. Par ailleurs, une série de pistes pour améliorer ces techniques sont proposées. Le troisième objectif était la mise en évidence des espèces les plus caractéristiques de la communauté, afin de désigner des espèces-cibles pour une étude trophique ultérieure. Nos résultats montrent que Apherusa chiereghinii, Aora spinicornis, Dexamine spiniventris, Caprella acanthifera acanthifera et Gammarella fucicola sont des espèces intéressantes pour le type d’étude envisagé. Quelques autres candidats potentiels peuvent être désignés, mais leur situation est moins évidente. Il est vraisemblable que, pour ce point comme pour la plupart des précédents, l’analyse des résultats d’un cycle annuel complet permettra de tirer des conclusions plus franches. [less ▲]