References of "Thys, I"
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See detailIn situ filtration responses of Daphnia galeata to changes in food quality
Darchambeau, François ULg; Thys, I.

in Journal of Plankton Research (2005), 27(3), 227-236

In the stoichiometric study of phyto-zooplankton interactions, a controversy exists about how Daphnia species regulate their feeding rate when submitted to low-quality food (i.e. high dietary carbon ... [more ▼]

In the stoichiometric study of phyto-zooplankton interactions, a controversy exists about how Daphnia species regulate their feeding rate when submitted to low-quality food (i.e. high dietary carbon:phosphorus [C:P] ratio). In this study, we gathered data over 3 years on in situ clearance rates of a Daphnia galeata population, by conducting grazing experiments from April 1998 to October 2000 in the Esch-sur-Sure reservoir (Grand-Duchy of Luxembourg). Observed clearance rates (2.5-13.5 mL individual(-1) day(-1), mean 7.0 mL individual(-1) day(-1)) were correlated with population and environmental variables. Mean body size of Daphnia individuals was the best predictor of clearance rate (r(2) = 0.639), followed by water temperature (r(2) = 0.262) and P concentration in the seston (r(2) <= 0.241). When combined with body size, seston C:P or nitrogen:P ratios provided the best predictive regression model of clearance rate (r(2) = 0.852-0.897). The clearance rate was always correlated negatively with P concentration in the food. Thus, Daphnia reacts to a decrease of food quality (i.e. higher C:P ratio) by an increase of its feeding rate. However, the filtration response to food quality was inhibited by high population density. We suggest that, when food quality is low and population density high, this inhibition may favour fitness of future conspecific generations. In conclusion, our results emphasize the effect of P availability on transfer rate of organic matter between lacustrian autotrophs and herbivores and pose questions about consequent effects on nutrient biogeochemical cycles. [less ▲]

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See detailInfluence of zooplankton stoichiometry on nutrient sedimentation in a lake system
Darchambeau, François ULg; Thys, I.; Leporcq, B. et al

in Limnology & Oceanography (2005), 50(3), 905-913

We explored rates and stoichiometry (C: N: P ratios) of sinking particles in a temperate reservoir during a 2-yr period. Plankton was sampled weekly, and a sediment trap placed below the metalimnion ... [more ▼]

We explored rates and stoichiometry (C: N: P ratios) of sinking particles in a temperate reservoir during a 2-yr period. Plankton was sampled weekly, and a sediment trap placed below the metalimnion collected sinking particles. There were no significant relationships between the stoichiometry of entrapped material and seston or zooplankton stoichiometry. However the differences in the entrapped C: P and N: P ratios between consecutive trap samplings were negatively correlated with the time variations of the zooplankton C: P and N: P ratios. Zooplankton C: P and N: P ratios were positively correlated with the percentage of copepod biomass in total zooplankton biomass > 250 mu m and negatively correlated with the percentage of cladocerans. Zooplankton biomass > 250 mu m reduced the fraction of N and P primary production lost to sinking (export ratio). The residuals of the N export ratio versus zooplankton biomass relationship were negatively correlated with the zooplankton N: P ratio, whereas there was a positive relationship with the residuals of the P export ratio relationship. These observations support the hypothesis that the regulation of elemental homeostasis in the herbivorous zooplankton consumers occurs at least partly at the assimilation/egestion level. Elements ingested in excess-P for the herbivorous copepods and N for many cladocerans-are concentrated into sinking feces, whereas the deficient elements are captured into biomass. [less ▲]

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See detailA note on the use of fluorescently labelled algae for the determination of gut passage time in Bosmina and Daphnia
Cauchie, Henry-Michel ULg; Deguée, N.; Joaquim-Justo, Célia ULg et al

in Verhandlungen der Internationalen Vereinigung für Theoretische und Angewandte Limnologie = Proceedings of the International Association of Theoretical and Applied Limnology (2001), 27

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See detailVariations saisonnières des isotopes stables du carbone (13C) et de l'azote (15N) dans un réservoir mésotrophe.
Hoffmann, Lucien; Willame, R.; Thys, I. et al

in Annales scientifiques de l'Université de Clermont-Ferrand 2 (2000, July), 108

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