19 research outputs found

    Omnivory by planktivores stabilizes plankton dynamics, but may either promote or reduce algal biomass

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    Classical models of phytoplankton–zooplankton interaction show that with nutrient enrichment such systems may abruptly shift from limit cycles to stable phytoplankton domination due to zooplankton predation by planktivorous fish. Such models assume that planktivorous fish eat only zooplankton, but there are various species of filter-feeding fish that may also feed on phytoplankton. Here, we extend these classical models to systematically explore the effects of omnivory by planktivorous fish. Our analysis indicates that if fish forage on phytoplankton in addition to zooplankton, the alternative attractors predicted by the classical models disappear for all realistic parameter settings, even if omnivorous fish have a strong preference for zooplankton. Our model also shows that the level of fish biomass above which zooplankton collapse should be higher when fish are omnivorous than when fish are zooplanktivorous. We also used the model to explore the potential effects of the now increasingly common practice of stocking lakes with filter-feeding fish to control cyanobacteria. Because omnivorous filter-feeding fish forage on phytoplankton as well as on the main grazers of phytoplankton, the net effect of such fish on the phytoplankton biomass is not obvious. Our model suggests that there may be a unimodal relationship between the biomass of omnivorous filter-feeding fish and the biomass of phytoplankton. This implies that to manage for reductions in phytoplankton biomass, heavy stocking or strong reduction of such fish is bes

    Omnivory by planktivores stabilizes plankton dynamics, but may either promote or reduce algal biomass

    Get PDF
    Classical models of phytoplankton–zooplankton interaction show that with nutrient enrichment such systems may abruptly shift from limit cycles to stable phytoplankton domination due to zooplankton predation by planktivorous fish. Such models assume that planktivorous fish eat only zooplankton, but there are various species of filter-feeding fish that may also feed on phytoplankton. Here, we extend these classical models to systematically explore the effects of omnivory by planktivorous fish. Our analysis indicates that if fish forage on phytoplankton in addition to zooplankton, the alternative attractors predicted by the classical models disappear for all realistic parameter settings, even if omnivorous fish have a strong preference for zooplankton. Our model also shows that the level of fish biomass above which zooplankton collapse should be higher when fish are omnivorous than when fish are zooplanktivorous. We also used the model to explore the potential effects of the now increasingly common practice of stocking lakes with filter-feeding fish to control cyanobacteria. Because omnivorous filter-feeding fish forage on phytoplankton as well as on the main grazers of phytoplankton, the net effect of such fish on the phytoplankton biomass is not obvious. Our model suggests that there may be a unimodal relationship between the biomass of omnivorous filter-feeding fish and the biomass of phytoplankton. This implies that to manage for reductions in phytoplankton biomass, heavy stocking or strong reduction of such fish is bes

    A Checklist of phytoplankton species around the Equator in GuaraĂ­ras, Galinhos and Diogo Lopes lagoons (Rio Grande do Norte, Brazil)

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    1 - Coastal lagoons show great fragility and vulnerability to the anthropogenic pressure. The understanding of physical, chemical, geological characteristics and ecological dynamics of lagoons is fundamental for planning the implementation of coastal management strategies in these ecosystems. The intrinsically high variability of phytoplankton communities in transitional environments should be taken into account not only because of phytoplankton ecological importance, but also because of the implications for environmental management.2 - The aim of this study is a general description of the phytoplankton community in three coastal lagoons situated in the Rio Grande do Norte region, at the Northeast of Brazil.3 - For the three lagoons, a total of 124 phytoplankton taxa were identified. In terms of species richness, diatoms were the largest group with 92 identified taxa belonging to 46 genera. At the class level, Bacillariophyceae recorded 39 taxa belonging to 18 genera; Coscinodiscophyceae recorded 39 taxa belonging to 21 genera and Fragilariophyceae recorded 14 taxa belonging to 7 genera. The group of the dinoflagellates recorded 15 taxa belonging to 6 genera and the Cyanophyceae was represented by 8 taxa belonging to 5 genera, including Trichodesmium erythraeum, a taxon related to toxic blooms

    Lower biodiversity of native fish but only marginally altered plankton biomass in tropical lakes hosting introduced piscivorous Cichla cf. ocellaris

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    We compared the species richness and abundance of fish, zooplankton and phytoplankton in nine mesotrophic coastal shallow lakes (Northeastern Brazil) with and without the exotic predator cichlid tucunarĂ© or ‘peacock bass’ (Cichla cf. ocellaris). We hypothesized that the introduction of tucunarĂ© would lead to decreased abundance and species diversity of native fish assemblages and cause indirect effects on the abundance and species diversity of the existing communities of zooplankton and phytoplankton and on water transparency. Our hypotheses were only partly confirmed. Although fish richness and diversity were, in fact, drastically lower in the lakes hosting tucunarĂ©, no significant differences were traced in total fish catch per unit of effort, zooplankton and phytoplankton biomass, plankton diversity or the zooplankton:phytoplankton biomass (TZOO:TPHYTO) ratio. However, zooplankton biomass and TZOO:TPHYTO tended to be higher and the phytoplankton biomass lower in lakes with tucunarĂ©. Our analyses therefore suggest that the introduction of tucunarĂ© had marked effect on the fish community structure and diversity in these shallow lakes, but only modest cascading effects on zooplankton and phytoplankton

    Ecological Literacy And Beyond: Problem-based Learning For Future Professionals

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    Ecological science contributes to solving a broad range of environmental problems. However, lack of ecological literacy in practice often limits application of this knowledge. In this paper, we highlight a critical but often overlooked demand on ecological literacy: to enable professionals of various careers to apply scientific knowledge when faced with environmental problems. Current university courses on ecology often fail to persuade students that ecological science provides important tools for environmental problem solving. We propose problem-based learning to improve the understanding of ecological science and its usefulness for real-world environmental issues that professionals in careers as diverse as engineering, public health, architecture, social sciences, or management will address. Courses should set clear learning objectives for cognitive skills they expect students to acquire. Thus, professionals in different fields will be enabled to improve environmental decision-making processes and to participate effectively in multidisciplinary work groups charged with tackling environmental issues. © 2014 Royal Swedish Academy of Sciences
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