| Accueil | << 1 2 3 4 5 6 7 8 9 >> |
|
Fouilland, E., Galès, A., Beaugelin, I., Lanouguère, E., Pringault, O., & Leboulanger, C. (2018). Influence of bacteria on the response of microalgae to contaminant mixtures. Chemosphere, 211, 449–455.
Résumé: When microalgae are exposed to contaminants, the role of associated bacteria within the phycosphere, the microenvironment surrounding algal cells, remains largely unknown. The present study investigated the importance of algae-associated bacteria on the responses of microalgae growth to metallic and organic toxicant exposure. The effects of a polluted sediment elutriate, and of metal or pesticide mixtures at environmentally relevant concentrations (<10 μg L−1) were assessed on the growth of two microalgae strains: Isochrysis galbana, a prymnesiophyte, and Thalassiosira delicatula, a centric diatom. Both cultures were maintained as axenic or bacterized under similar conditions in batch cultures. In axenic conditions, the metal mixture addition at low concentrations alleviated limitation of growth by metals for T. delicatula relative to control, but inhibited I. galbana growth at highest concentration. In similar axenic conditions, both T. delicatula and I. galbana growth were negatively inhibited by pesticide mixture at concentrations as low as 10 ng L−1. The bacterial diversities associated with the two microalgae strains were significantly different (Bray–Curtis dissimilarity greater than 0.9) but their impact on microalgae growth was similar. The presence of bacteria reduced algal growth rate by ca. 50% compared to axenic cultures, whereas no significant effect of sediment elutriate, metal or pesticide mixtures was noticed on non-axenic algal growth rates. These results show that bacteria may have a negative effect on algal growth but can reduce pesticide toxicity or metal availability to algae.
|
|
Fouilland, E., Tolosa, I., Bonnet, D., Bouvier, C., Bouvier, T., Bouvy, M., et al. (2014). Bacterial carbon dependence on freshly produced phytoplankton exudates under different nutrient availability and grazing pressure conditions in coastal marine waters. FEMS microbiology ecology, 87(3), 757–769.
Résumé: The effects of grazing pressure and inorganic nutrient availability on the direct carbon transfer from freshly produced phytoplankton exudates to heterotrophic bacteria biomass production were studied in Mediterranean coastal waters. The short-term incorporation of (1)(3)C (H(1)(3)CO(3)) in phytoplankton and bacterial lipid biomarkers was measured as well as the total bacterial carbon production (BP), viral lysis and the microbial community structure under three experimental conditions: (1) High inorganic Nutrient and High Grazing (HN + HG), (2) High inorganic Nutrient and Low Grazing (HN + LG) and (3) under natural in situ conditions with Low inorganic Nutrient and High Grazing (LN + HG) during spring. Under phytoplankton bloom conditions (HN + LG), the bacterial use of freshly produced phytoplankton exudates as a source of carbon, estimated from (1)(3)C enrichment of bacterial lipids, contributed more than half of the total bacterial production. However, under conditions of high grazing pressure on phytoplankton with or without the addition of inorganic nutrients (HN + HG and LN + HG), the (1)(3)C enrichment of bacterial lipids was low compared with the high total bacterial production. BP therefore seems to depend mainly on freshly produced phytoplankton exudates during the early phase of phytoplankton bloom period. However, BP seems mainly relying on recycled carbon from viral lysis and predators under high grazing pressure.
Mots-Clés: bacteria; carbon coupling; coastal waters; interactions; phytoplankton
|
|
Galiana, N., Lurgi, M., Claramunt-Lopez, B., Fortin, M. - J., Leroux, S., Cazelles, K., et al. (2018). The spatial scaling of species interaction networks. Nat. Ecol. Evol., 2(5), 782–790.
Résumé: Species-area relationships (SARs) are pivotal to understand the distribution of biodiversity across spatial scales. We know little, however, about how the network of biotic interactions in which biodiversity is embedded changes with spatial extent. Here we develop a new theoretical framework that enables us to explore how different assembly mechanisms and theoretical models affect multiple properties of ecological networks across space. We present a number of testable predictions on network-area relationships (NARs) for multi-trophic communities. Network structure changes as area increases because of the existence of different SARs across trophic levels, the preferential selection of generalist species at small spatial extents and the effect of dispersal limitation promoting beta-diversity. Developing an understanding of NARs will complement the growing body of knowledge on SARs with potential applications in conservation ecology. Specifically, combined with further empirical evidence, NARs can generate predictions of potential effects on ecological communities of habitat loss and fragmentation in a changing world.
|
|
Gravel, D., Poisot, T., Albouy, C., Velez, L., & Mouillot, D. (2013). Inferring food web structure from predator-prey body size relationships. Methods in Ecology and Evolution, 4(11), 1083–1090.
Résumé: 1. Current global changes make it important to be able to predict which interactions will occur in the emerging ecosystems. Most of the current methods to infer the existence of interactions between two species require a good knowledge of their behaviour or a direct observation of interactions. In this paper, we overcome these limitations by developing a method, inspired from the niche model of food web structure, using the statistical relationship between predator and prey body size to infer the matrix of potential interactions among a pool of species. 2. The novelty of our approach is to infer, for any species of a given species pool, the three species-specific parameters of the niche model. The method applies to both local and metaweb scales. It allows one to evaluate the feeding interactions of a new species entering the community. 3. We find that this method gives robust predictions of the structure of food webs and that its efficiency is increased when the strength of the body-size relationship between predators and preys increases. 4. We finally illustrate the potential of the method to infer the metaweb structure of pelagic fishes of the Mediterranean sea under different global change scenarios.
|
|
Guilhaumon, F., Krasnov, B. R., Poulin, R., Shenbrot, G. I., & Mouillot, D. (2012). Latitudinal mismatches between the components of mammal-flea interaction networks. Glob. Ecol. Biogeogr., 21(7), 725–731.
Résumé: Aim The large-scale description of ecosystem complexity, including the structure of interaction networks, has been largely overlooked although it is known to underpin species co-occurrences and their robustness to climatic or anthropogenic disturbances. Here, we investigated whether the various components of mammalflea interaction networks (richness of fleas, richness of mammals and the richness of mammalflea associations) are spatially congruent and follow the latitudinal diversity gradient (LDG). Location Sixteen regions, world-wide. Methods We first took into account the effect of area on diversity by determining the position of regions with respect to speciesarea relationships. We then investigated the spatial congruence between the regional richness of each component of mammalflea interaction networks as well as their latitudinal gradients. We further investigated patterns for fleahost associations by testing for relationships between mammalflea interaction richness and (1) flea niche breadth and (2) host carrying capacity. Results We report divergent LDGs for the different components of mammalflea interaction networks: our data agree with a canonical LDG for mammals, but reveal that the diversity of fleas and mammalflea associations do not follow such a classical gradient. Our results suggest that host carrying capacity is more likely than flea niche breadth to modulate the number of links in hostparasite interaction networks. Main conclusions The complex interplay between geographic variation in host diversity and both host and parasite traits can lead to unexpected spatial patterns such as the invalidation of expected parasites and links in hostparasite web LDGs. Beyond our focus on hostparasite interactions, our study is among the first in the emerging field of interaction network macroecology and paves the way for other components of ecological networks to be investigated across space and time.
|