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Auteur Canard, E.F.; Mouquet, N.; Mouillot, D.; Stanko, M.; Miklisova, D.; Gravel, D. url  doi
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  Titre Empirical Evaluation of Neutral Interactions in Host-Parasite Networks Type Article scientifique
  Année 2014 Publication Revue Abrégée American Naturalist  
  Volume 183 Numéro 4 Pages 468-479  
  Mots-Clés abundance; animal mutualistic networks; community; dissimilarity; effort; food-web structure; geographical variation; host-parasite network; network structure; neutrality; null model; phylogenetic signal; reconciling niche; sampling; scale-dependence; species abundance distribution  
  Résumé While niche-based processes have been invoked extensively to explain the structure of interaction networks, recent studies propose that neutrality could also be of great importance. Under the neutral hypothesis, network structure would simply emerge from random encounters between individuals and thus would be directly linked to species abundance. We investigated the impact of species abundance distributions on qualitative and quantitative metrics of 113 host-parasite networks. We analyzed the concordance between neutral expectations and empirical observations at interaction, species, and network levels. We found that species abundance accurately predicts network metrics at all levels. Despite host-parasite systems being constrained by physiology and immunology, our results suggest that neutrality could also explain, at least partially, their structure. We hypothesize that trait matching would determine potential interactions between species, while abundance would determine their realization.  
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  ISSN (up) 0003-0147 ISBN Médium  
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  Numéro d'Appel MARBEC @ isabelle.vidal-ayouba @ collection 573  
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Auteur Valls, A.; Coll, M.; Christensen, V. url  doi
openurl 
  Titre Keystone species : toward an operational concept for marine biodiversity conservation Type Article scientifique
  Année 2015 Publication Ecological Monographs Revue Abrégée  
  Volume 85 Numéro 1 Pages 29-47  
  Mots-Clés classification tree; Ecopath model; food-web structure; index of keystoneness; keystone species; marine ecosystems; Meta-analysis; mixed-trophic impact; rank correlation tests; scoring method  
  Résumé Various definitions and indices have been proposed in the literature to identify keystone species. In this study, we intended to make the concept of keystone species operational for marine biodiversity conservation. We used an exclusive definition of keystone species, based on the original concept of keystone predator, and derived a new functional index of keystoneness (KS) from an ecosystem-modeling approach. First, several KS indices were formulated, by combining measures of the mixed-trophic impact (MTI) and biomass of species. Then, a meta-analysis was performed, based on 101 published Ecopath food-web models, selected with a scoring method, and representative of the variety of marine ecosystems worldwide. The indices were applied to the models, and two statistical methods were compared to select the most promising KS index. Rank correlation tests were performed to assess the balance between the contribution of the impact and biomass components to the different KS indices. In addition, a classification tree was implemented, based on ecosystem-specific thresholds applied to the latter species traits, and used to confirm the identified keystone species. The selected index obtained the highest number of models with positive results from both the rank correlation tests and the classification tree. We also demonstrated the limitations of existing KS indices previously applied in the literature. Species were ranked according to their estimates of keystoneness with the selected KS index, so that potential keystone species were quantitatively identified in the 101 modeled food webs. The standardized modeling approach allowed for a comparison of the identified keystone species across models: cartilaginous fishes and toothed whales obtained the highest occurrences. Finally, the selected KS index was applied to the well-known case study of Prince William Sound (Alaska, USA). Potentially significant anthropogenic (fishing) impacts on keystone species were also considered and discussed. The operational methodology presented is directly applicable to marine food webs, and may be adapted to other (freshwater or terrestrial) systems.  
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  ISSN (up) 0012-9615 ISBN Médium  
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  Numéro d'Appel MARBEC @ isabelle.vidal-ayouba @ collection 1114  
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Auteur Meddeb, M.; Grami, B.; Chaalali, A.; Haraldsson, M.; Niquil, N.; Pringault, O.; Sakka Hlaili, A. url  doi
openurl 
  Titre Plankton food-web functioning in anthropogenically impacted coastal waters (SW Mediterranean Sea): an ecological network analysis Type Article scientifique
  Année 2018 Publication Revue Abrégée Progress in Oceanography  
  Volume Numéro Pages  
  Mots-Clés Ecological Network Analysis; Food-web modelling; Mediterranean coastal waters; plankton ecology  
  Résumé The study is the first attempt to (i) model spring food webs in three SW Mediterranean ecosystems which are under different anthropogenic pressures and (ii) to project the consequence of this stress on their function. Linear inverse models were built using the Monte Carlo method coupled with Markov Chains to characterize the food-web status of the Lagoon, the Channel (inshore waters under high eutrophication and chemical contamination) and the Bay of Bizerte (offshore waters under less anthropogenic pressure). Ecological network analysis was used for the description of structural and functional properties of each food web and for inter-ecosystem comparisons. Our results showed that more carbon was produced by phytoplankton in the inshore waters (966–1234 mg C m-2 d-1) compared to the Bay (727 mg C m-2 d-1). The total ecosystem carbon inputs into the three food webs was supported by high primary production, which was mainly due to >10µm algae. However, the three carbon pathways were characterized by low detritivory and a high herbivory which was mainly assigned to protozooplankton. This latter was efficient in channelling biogenic carbon. In the Lagoon and the Channel, foods webs acted almost as a multivorous structure with a tendency towards herbivorous one, whereas in the Bay the herbivorous pathway was more dominant. Ecological indices revealed that the Lagoon and the Channel food webs/systems had high total system throughput and thus were more active than the Bay. The Bay food web, which had a high relative ascendency value, was more organized and specialized. This inter–ecosystem difference could be due to the varying levels of anthropogenic impact among sites. Indeed, the low value of Finn’s cycling index indicated that the three systems are disturbed, but the Lagoon and the Channel, with low average path lengths, appeared to be more stressed, as both sites have undergone higher chemical pollution and nutrient loading. This study shows that ecosystem models combined with ecological indices provide a powerful approach to detect change in environmental status and anthropogenic impacts.  
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  ISSN (up) 0079-6611 ISBN Médium  
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  Numéro d'Appel MARBEC @ alain.herve @ collection 2292  
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Auteur Deininger, A.; Faithfull, C.L.; Lange, K.; Bayer, T.; Vidussi, F.; Liess, A. doi  openurl
  Titre Simulated terrestrial runoff triggered a phytoplankton succession and changed seston stoichiometry in coastal lagoon mesocosms Type Article scientifique
  Année 2016 Publication Revue Abrégée Mar. Environ. Res.  
  Volume 119 Numéro Pages 40-50  
  Mots-Clés climate change; communities; community composition; Diatoms; dynamics; ecosystems; events; food-web; growth; Mediterranean; Mesocosm; Phytoplankton; plankton; productivity; river flash-flood; schelde; soil; Stoichiometry; Thau lagoon  
  Résumé Climate change scenarios predict intensified terrestrial storm runoff, providing coastal ecosystems with large nutrient pulses and increased turbidity, with unknown consequences for the phytoplankton community. We conducted a 12-day mesocosm experiment in the Mediterranean Thau Lagoon (France), adding soil (simulated runoff) and fish (different food webs) in a 2 x 2 full factorial design and monitored phytoplankton composition, shade adaptation and stoichiometry. Diatoms (Chaetoceros) increased fourfold immediately after soil addition, prymnesiophytes and dinoflagellates peaked after six- and 12 days, respectively. Soil induced no phytoplanlcton shade adaptation. Fish reduced the positive soil effect on dinoflagellates (Scripsiella, Glenodinium), and diatom abundance in general. Phytoplankton community composition drove seston stoichiometry. In conclusion, pulsed terrestrial runoff can cause rapid, low quality (high carbon: nutrient) diatom blooms. However, bloom duration may be short and reduced in magnitude by fish. Thus, climate change may shift shallow coastal ecosystems towards famine or feast dynamics. (C) 2016 Elsevier Ltd. All rights reserved.  
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  ISSN (up) 0141-1136 ISBN Médium  
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  Numéro d'Appel MARBEC @ alain.herve @ collection 2063  
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Auteur Brosset, P.; Le Bourg, B.; Costalago, D.; Banaru, D.; Van Beveren, E.; Bourdeix, J.-H.; Fromentin, J.-M.; Menard, F.; Saraux, C. doi  openurl
  Titre Linking small pelagic dietary shifts with ecosystem changes in the Gulf of Lions Type Article scientifique
  Année 2016 Publication Revue Abrégée Mar. Ecol.-Prog. Ser.  
  Volume 554 Numéro Pages 157-171  
  Mots-Clés anchovy; anchovy engraulis-encrasicolus; climate; Dietary overlap; fish; food-web; NW Mediterranean; nw mediterranean sea; plankton; regime shifts; Sardine; size-fractionated zooplankton; southern benguela; Sprat; stable-isotope ratios; Trophic ecology  
  Résumé Since 2008, a severe decrease in size and body condition together with a demographic truncation has been observed in the sardine (secondarily in anchovy) population of the Gulf of Lions (NW Mediterranean Sea). In parallel, sprat biomass, which was negligible before, has increased tenfold. All of these changes have strongly affected the regional fisheries. Using trophic and isotopic data from contrasting periods of low versus high growth and condition, we investigated potential changes in diet and interspecific feeding interactions through time. Evidence of resource partitioning was found between sprat and both anchovy and sardine in 2004 and 2005. Since 2010, the isotopic niches of the 3 species have tended to overlap, suggesting higher risk of competition for food resources. Moreover, the wider trophic niche of sprat indicates higher variability in individual diets. Anchovy and sardine diet varied through time, with a high proportion of large copepods or cladocerans in periods of high growth and condition (1994 and 2007, respectively) versus a dominance of small copepods in the present (2011-2012). Furthermore, an important reduction in prey diversity was also identified in the diet of both anchovy and sardine during the most recent period. Our results support the hypothesis that changes in small pelagic fish growth, size and body condition and ultimately biomass could be due to bottom-up control characterized by changes in food availability and increasing potential trophic competition.  
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  Numéro d'Appel MARBEC @ alain.herve @ collection 1642  
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