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Sökning: WFRF:(van Nes Egbert H.)

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1.
  • Downing, Andrea S., et al. (författare)
  • Coupled human and natural system dynamics as key to the sustainability of Lake Victoria's ecosystem services
  • 2014
  • Ingår i: Ecology & Society. - 1708-3087. ; 19:4, s. 31-
  • Tidskriftsartikel (refereegranskat)abstract
    • East Africa's Lake Victoria provides resources and services to millions of people on the lake's shores and abroad. In particular, the lake's fisheries are an important source of protein, employment, and international economic connections for the whole region. Nonetheless, stock dynamics are poorly understood and currently unpredictable. Furthermore, fishery dynamics are intricately connected to other supporting services of the lake as well as to lakeshore societies and economies. Much research has been carried out piecemeal on different aspects of Lake Victoria's system; e.g., societies, biodiversity, fisheries, and eutrophication. However, to disentangle drivers and dynamics of change in this complex system, we need to put these pieces together and analyze the system as a whole. We did so by first building a qualitative model of the lake's social-ecological system. We then investigated the model system through a qualitative loop analysis, and finally examined effects of changes on the system state and structure. The model and its contextual analysis allowed us to investigate system-wide chain reactions resulting from disturbances. Importantly, we built a tool that can be used to analyze the cascading effects of management options and establish the requirements for their success. We found that high connectedness of the system at the exploitation level, through fisheries having multiple target stocks, can increase the stocks' vulnerability to exploitation but reduce society's vulnerability to variability in individual stocks. We describe how there are multiple pathways to any change in the system, which makes it difficult to identify the root cause of changes but also broadens the management toolkit. Also, we illustrate how nutrient enrichment is not a self-regulating process, and that explicit management is necessary to halt or reverse eutrophication. This model is simple and usable to assess system-wide effects of management policies, and can serve as a paving stone for future quantitative analyses of system dynamics at local scales.
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2.
  • Mooij, Wolf M., et al. (författare)
  • Serving many at once : How a database approach can create unity in dynamical ecosystem modelling
  • 2014
  • Ingår i: Environmental Modelling & Software. - 1364-8152 .- 1873-6726. ; 61, s. 266-273
  • Tidskriftsartikel (refereegranskat)abstract
    • Simulation modelling in ecology is a field that is becoming increasingly compartmentalized. Here we propose a Database Approach To Modelling (DATM) to create unity in dynamical ecosystem modelling with differential equations. In this approach the storage of ecological knowledge is independent of the language and platform in which the model will be run. To create an instance of the model, the information in the database is translated and augmented with the language and platform specifics. This process is automated so that a new instance can be created each time the database is updated. We describe the approach using the simple Lotka-Volterra model and the complex ecosystem model for shallow lakes PCLake, which we automatically implement in the frameworks OSIRIS, GRIND for MATLAB, ACSL, R, DUFLOW and DELWAQ. A clear advantage of working in a database is the overview it provides. The simplicity of the approach only adds to its elegance.
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3.
  • van Gerven, Luuk P. A., et al. (författare)
  • Advantages of concurrent use of multiple software frameworks in water quality modelling using a database approach
  • 2015
  • Ingår i: Fundamental and Applied Limnology. - 1863-9135. ; 186:1-2, s. 5-20
  • Tidskriftsartikel (refereegranskat)abstract
    • Water quality modelling deals with multidisciplinary questions ranging from fundamental to applied. Addressing this broad range of questions requires multiple analysis techniques and therefore multiple frameworks. Through the recently developed database approach to modelling (DATM), it has become possible to run a model in multiple software frameworks without much overhead. Here we apply DATM to the ecosystem model for ditches PCDitch and its twin model for shallow lakes PCLake. Using DATM, we run these models in six frameworks (ACSL, DELWAQ, DUFLOW, GRIND for MATLAB, OSIRIS and R), and report on the possible model analyses with tools provided by each framework. We conclude that the dynamic link between frameworks and models resulting from DATM has the following main advantages: it allows one to use the framework one is familiar with for most model analyses and eases switching between frameworks for complementary model analyses, including the switch between a 0-D and 1-D to 3-D setting. Moreover, the strength of each framework - including runtime performance - can now be easily exploited. We envision that a community-based further development of the concept can contribute to the future development of water quality modelling, not only by addressing multidisciplinary questions but also by facilitating the exchange of models and process formulations within the community of water quality modellers.
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4.
  • Downing, Andrea S., et al. (författare)
  • Effects of resources and mortality on the growth and reproduction of Nile perch in Lake Victoria
  • 2013
  • Ingår i: Freshwater Biology. - 0046-5070 .- 1365-2427. ; 58:4, s. 828-840
  • Tidskriftsartikel (refereegranskat)abstract
    • 1. A collapse of Nile perch stocks of Lake Victoria could affect up to 30million people. Furthermore, changes in Nile perch population size-structure and stocks make the threat of collapse imminent. However, whether eutrophication or fishing will be the bane of Nile perch is still debated. 2. Here, we attempt to unravel how changes in food resources, a side effect of eutrophication, and fishing mortality determine fish population growth and size structures. We parameterised a physiologically structured model to Nile perch, analysed the influence of ontogenetic diet shifts and relative resource abundances on existence boundaries of Nile perch and described the populations on either side of these boundaries. 3. Our results showed that ignoring ontogenetic diet shifts can lead to over-estimating the maximum sustainable mortality of a fish population. Size distributions can be indicators of processes driving population dynamics. However, the vulnerability of stocks to fishing mortality is dependent on its environment and is not always reflected in size distributions. 4. We suggest that the ecosystem, instead of populations, should be used to monitor long-term effects of human impact.
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5.
  • Scheffer, Marten, et al. (författare)
  • The Evolution of Functionally Redundant Species; Evidence from Beetles
  • 2015
  • Ingår i: PLOS ONE. - [Scheffer, Marten; Vergnon, Remi; van Nes, Egbert H.; Cuppen, Jan G. M.; Peeters, Edwin T. H. M.] geningen Univ, Dept Aquat Ecol & Water Qual Management, NL-6700 AA Wageningen, Netherlands. [Leijs, Remko] S Australian Museum, Adelaide, SA 5000, Australia. [Leijs, Remko] Univ Adelaide, Sch Earth & Environm Sci, Adelaide, SA, Australia. [Leijs, Remko] Flinders Univ South Australia, Sch Biol Sci, Adelaide, SA, Australia. [Nilsson, Anders N.] Umea Univ, Dept Ecol & Environm Sci, S-90187 Umea, Sweden.. - 1932-6203. ; 10:10
  • Tidskriftsartikel (refereegranskat)abstract
    • While species fulfill many different roles in ecosystems, it has been suggested that numerous species might actually share the same function in a near neutral way. So-far, however, it is unclear whether such functional redundancy really exists. We scrutinize this question using extensive data on the world's 4168 species of diving beetles. We show that across the globe these animals have evolved towards a small number of regularly-spaced body sizes, and that locally co-existing species are either very similar in size or differ by at least 35%. Surprisingly, intermediate size differences (10-20%) are rare. As body-size strongly reflects functional aspects such as the food that these generalist predators can eat, these beetles thus form relatively distinct groups of functional look-a-likes. The striking global regularity of these patterns support the idea that a self-organizing process drives such species-rich groups to self-organize evolutionary into clusters where functional redundancy ensures resilience through an insurance effect.
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6.
  • Staal, Arie, et al. (författare)
  • Hysteresis of tropical forests in the 21st century
  • 2020
  • Ingår i: Nature Communications. - 2041-1723 .- 2041-1723. ; 11:1
  • Tidskriftsartikel (refereegranskat)abstract
    • Tropical forests modify the conditions they depend on through feedbacks at different spatial scales. These feedbacks shape the hysteresis (history-dependence) of tropical forests, thus controlling their resilience to deforestation and response to climate change. Here, we determine the emergent hysteresis from local-scale tipping points and regional-scale forest-rainfall feedbacks across the tropics under the recent climate and a severe climate-change scenario. By integrating remote sensing, a global hydrological model, and detailed atmospheric moisture tracking simulations, we find that forest-rainfall feedback expands the geographic range of possible forest distributions, especially in the Amazon. The Amazon forest could partially recover from complete deforestation, but may lose that resilience later this century. The Congo forest currently lacks resilience, but is predicted to gain it under climate change, whereas forests in Australasia are resilient under both current and future climates. Our results show how tropical forests shape their own distributions and create the climatic conditions that enable them. Tropical rainforests partly create their own climatic conditions by promoting precipitation, therefore rainforest losses may trigger dramatic shifts. Here the authors combine remote sensing, hydrological modelling, and atmospheric moisture tracking simulations to assess forest-rainfall feedbacks in three major tropical rainforest regions on Earth and simulate potential changes under a severe climate change scenario.
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7.
  • Carpenter, Stephen R., et al. (författare)
  • Allowing variance may enlarge the safe operating space for exploited ecosystems
  • 2015
  • Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - 0027-8424 .- 1091-6490. ; 112:46, s. 14384-14389
  • Tidskriftsartikel (refereegranskat)abstract
    • Variable flows of food, water, or other ecosystem services complicate planning. Management strategies that decrease variability and increase predictability may therefore be preferred. However, actions to decrease variance over short timescales (2-4 y), when applied continuously, may lead to long-term ecosystem changes with adverse consequences. We investigated the effects of managing short-term variance in three well-understood models of ecosystem services: lake eutrophication, harvest of a wild population, and yield of domestic herbivores on a rangeland. In all cases, actions to decrease variance can increase the risk of crossing critical ecosystem thresholds, resulting in less desirable ecosystem states. Managing to decrease short-term variance creates ecosystem fragility by changing the boundaries of safe operating spaces, suppressing information needed for adaptive management, cancelling signals of declining resilience, and removing pressures that may build tolerance of stress. Thus, the management of variance interacts strongly and inseparably with the management of resilience. By allowing for variation, learning, and flexibility while observing change, managers can detect opportunities and problems as they develop while sustaining the capacity to deal with them.
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8.
  • Downing, Andrea S., et al. (författare)
  • Was Lates Late? : A Null Model for the Nile Perch Boom in Lake Victoria
  • 2013
  • Ingår i: PLOS ONE. - 1932-6203. ; 8:10, s. e76847-
  • Tidskriftsartikel (refereegranskat)abstract
    • Nile perch (Lates niloticus) suddenly invaded Lake Victoria between 1979 and 1987, 25 years after its introduction in the Ugandan side of the lake. Nile perch then replaced the native fish diversity and irreversibly altered the ecosystem and its role to lakeshore societies: it is now a prised export product that supports millions of livelihoods. The delay in the Nile perch boom led to a hunt for triggers of the sudden boom and generated several hypotheses regarding its growth at low abundances - all hypotheses having important implications for the management of Nile perch stocks. We use logistic growth as a parsimonious null model to predict when the Nile perch invasion should have been expected, given its growth rate, initial stock size and introduction year. We find the first exponential growth phase can explain the timing of the perch boom at the scale of Lake Victoria, suggesting that complex mechanisms are not necessary to explain the Nile perch invasion or its timing. However, the boom started in Kenya before Uganda, indicating perhaps that Allee effects act at smaller scales than that of the whole Lake. The Nile perch invasion of other lakes indicates that habitat differences may also have an effect on invasion success. Our results suggest there is probably no single management strategy applicable to the whole lake that would lead to both efficient and sustainable exploitation of its resources.
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  • Resultat 1-8 av 8

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