Kooperativer Bibliotheksverbund

Berlin Brandenburg

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  • 1
    In: Journal of Plankton Research, 2012, Vol. 34(10), pp.922-927
    Description: Ingestion of the large pelagic ciliates Stentor araucanus and S. amethystinus by the cyclopoid copepod Mesocyclops araucanus was independent of light conditions and copepod sex, but rates were twice as high on S. araucanus as on S. amethystinus . Copepods consumed 44–183% of their biomass daily. Absorption efficiency was 5–40%, while 20–30% of the ingested food was found in the faeces. In field samples, 32–93% of Mesocyclops had ingested Stentor, indicating the importance of this food source.
    Keywords: Predation ; Cyclopoid Copepods ; Mixotrophic Ciliates ; 〈Kwd〉〈Italic〉Stentor〈/Italic〉〈/Kwd〉 ; North Patagonian Lakes
    ISSN: 0142-7873
    E-ISSN: 1464-3774
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  • 2
    In: Journal of Plankton Research, 2012, Vol. 34(2), pp.102-112
    Description: Aquatic bacteria are considered to exhibit a paradoxical behaviour. They luxuriously consume phosphorus, the element often restricting the abundance of algae, which provide the organic substrates maintaining bacterial growth. Here, we test the hypothesis that bacteria can limit their uptake of phosphorus and increase the availability of phosphorus to algae. The physiological costs for bacteria must be compensated for by a surplus of photosynthetic exudates facilitating higher biomass production. To test the potential of such an economic behaviour, we used a new differential equation model that was parameterized by independent experiments. Model results indicate that this potential does exist. As a consequence, we conducted continuous growth chemostat experiments. Bacteria did not leave more phosphorus to, “high exudation” algae compared with algae with low release. Therefore, the hypothesis was not supported by the experiments. However, bacteria significantly increased production 1.4–1.8-fold in cultures with “high exudation” algae. This was explained by an increase in conversion of organic carbon from growth medium into bacteria biomass. Algal exudates were quantitatively negligible but could act as growth factors. The results show that biomass of algae and bacteria cannot be predicted solely by mineral nutrients and carbon as assumed by the classical theory.
    Keywords: Bacteria ; Phytoplankton ; Exudation ; Phosphorus ; Differential Equation Model
    ISSN: 0142-7873
    E-ISSN: 1464-3774
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  • 3
    In: Journal of Plankton Research, 2006, Vol.28(7), pp.707-718
    Description: To test the consequences of decreased diversity and exclusion of keystone species, we compared the planktonic food webs in two acidic (pH3), species-poor mining lakes with those in two species-rich, neutral lakes. The ratio of heterotrophic to autotrophic biomass (H/A) was similar in acidic and neutral lakes with comparable productivity. However, food webs in both acidic lakes were largely restricted to two trophic levels in contrast to the four levels found in neutral lakes. This restriction in food chain length was attributed to the absence of efficient secondary consumers, rather than to productivity or lake size which resulted in unusually low predatorprey weight ratios, with small top predators hardly exceeding their prey in size. In contrast to the neutral lakes, plankton biomass size spectra of acidic lakes were discontinuous due to a lack of major functional groups. The unique size-dependence of feeding modes in pelagic food webs, with bacteria in the smallest size classes followed by autotrophs, herbivores and carnivores, was maintained for bacteria but the other feeding modes strongly overlapped in size. Thus, their characteristic succession along the size gradient was roughly preserved under extreme conditions but the flow of energy along the size gradient was truncated in the acidic lakes. For most but not all attributes studied, differences were larger between acidic and neutral lakes than between neutral lakes of different trophic state.
    Keywords: Feeding ; Plankton Surveys ; Food Chains ; Predation ; Carnivores ; Predators ; Biomass ; Trophic Levels ; Lakes ; Herbivores ; Interspecific Relationships ; Predator Prey Interactions ; Species Diversity ; Consumers ; Mining ; Prey ; Plankton ; Food Webs ; Plankton Surveys ; Feeding ; Food Chains ; Predation ; Carnivores ; Predators ; Biomass ; Succession ; Trophic Levels ; Keystone Species ; Predator-Prey Interactions ; Lakes ; Herbivores ; Interspecific Relationships ; Structure-Function Relationships ; Species Diversity ; Consumers ; Mining ; Prey ; Plankton ; Food Webs ; Freshwater ; Ecosystems and Energetics ; Effects on Organisms ; Ecosystem and Ecology Studies ; Ecology;
    ISSN: 0142-7873
    E-ISSN: 1464-3774
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  • 4
    In: Journal of Plankton Research, 2009, Vol. 31(8), pp.899-907
    Description: We investigated the response of the microbial components of the pelagic food web to re-oligotrophication of large, deep Lake Constance where total phosphorus concentrations during mixing decreased from a maximum of 2.81 μmol L −1 in 1979 via 1.87 μmol L −1 in 1987 to 0.26 μmol L −1 in 2007. Measurements of heterotrophic bacteria, autotrophic picoplankton (APP) and heterotrophic nanoflagellates (HNF) in 2006 and 2007 were compared to values from 1987 to 1997. We hypothesized that the biomass and seasonal variability of all groups will decrease under more oligotrophic conditions due to reduced resource availability, particularly for APP and HNF but less for the competitively stronger bacteria. Average bacterial biomass between spring and autumn was unrelated to phosphorus, whereas the ratio of bacterial biomass to chlorophyll a concentration increased with decreasing trophy due to declining chlorophyll concentrations. In contrast, a unimodal relationship was found between APP and phosphorus with low biomass at low and high phosphorus concentrations and maximum biomass in between. Average HNF biomass decreased strongly by a factor of 10–30 with decreasing trophy, and chlorophyll-specific HNF biomass was unimodally related to phosphorus. The relative seasonal biomass variability did not change for any group during re-oligotrophication. To conclude, HNF responded much more strongly and bacteria less so than chlorophyll concentrations to oligotrophication, whereas APP exhibited a more complex pattern.
    Keywords: Biology ; Oceanography ; Ecology;
    ISSN: 0142-7873
    E-ISSN: 1464-3774
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