1,720,985 research outputs found
Towards a sustainable use of water resources: a whole-ecosystem approach using network analysis
No full textLinking trophic position and flow structure constraints in ecological networks: energy transfer efficiency or topology effect?
No full textIn the present work we investigate whether the distribution of energy flows in ecosystems responds to criteria of trophic organization. We analyzed weighted and unweighted food webs estimating, for each node, trophic position (TP), Shannon's index of inflow diversity (H) and individual contribution to the whole average mutual information (AMI). Finally, we performed the same analysis on simulated webs that were constructed using the following criteria: (a) preserving topology and varying link strength; (b) modifying position of links and their intensities. In real ecosystems, moving toward top species, higher pathway redundancy coupled to a strong specialistic trophic behavior was observed. This means that, beside the availability of multiple topological routes, top predators tend to establish "bipolar" predator-prey interactions feeding on preferred preys that, in turn, are mainly preyed by that : specialized consumer. Although the analysis shows that, in qualitative food webs, links should be more numerous at the top of the trophic hierarchy, with magnitude more evenly distributed among the interactions, in weighted networks, the tendency of sharing the main flow between donor and receiving compartments (i.e. "bipolar" predator-prey interaction) increases from basal to top species. Patterns displayed by empirical data vanish when indices are calculated for simulated networks, pointing out how topology of energy delivery and flow intensities may be read as a function of the trophic hierarchy
L'uso dell'acqua in ambito urbano: un approccio ecosistemico per valutarne la sostenibilità
No full textUso sostenibile della risorsa acqua: un approccio ecosistemico mediante network analysis
No full textL'ecosistema e le sue relazioni. Idee e strumenti per la valutazione di impatto ambientale e di incidenza
No full textInsights into the processing of carbon in the South Florida Cypress Wetlands: a whole-ecosystem approach using network analysis
No full textQuantitative versus qualitative modelling. Acomplementary approach in ecosystem study.
No full textNatural disturbance or human perturbation act upon ecosystems by changing some dynamical parameters of one or more species. Foreseeing these modifications is necessary before embarking on an intervention: predictions may help to assess management options and define hypothesis for interventions. Models become valuable tools for studying and making predictions only when they capture types of interactions and their magnitude. Quantitative models are more precise and specific about a system, but require a large effort in model construction. Because of this very often ecological systems remain only partially specified and one possible approach to their description and analysis comes from qualitative modelling. Qualitative models yield predictions as directions of change in species abundance but in complex systems these predictions are often ambiguous, being the result of opposite actions exerted on the same species by way of multiple pathways of interactions. Again. to avoid such ambiguities one needs to know the intensity of all links in the system. One way to make link magnitude explicit in a way that can be used in qualitative analysis is described in this paper and takes advantage of another type of ecosystem representation: ecological flow networks. These flow diagrams contain the structure, the relative position and the connections between the components of a system, and the quantity of matter flowing along every connection. in this paper it is shown how these ecological flow networks can be used to produce a quantitative model similar to the qualitative counterpart. Analyzed through the apparatus of loop analysis this quantitative model yields predictions that are by no means ambiguous, solving in an elegant way the basic problem of qualitative analysis. The approach adopted in this work is still preliminary and we must be careful in its application
Secondary extinctions in ecological networks: bottlenecks unveiled
No full textIn ecosystems, a single extinction event could eventually precipitate in a mass extinction, involving species that may be several connections away from the target of the perturbation. This topic has been illuminated by recent studies on network mechanics, thanks to the concepts of hub, error and targeted removal, attack sensitivity, small world, and so forth. To forecast the effects of a species removal one can use an algorithm that unfolds a complex food web into a topologically simpler scheme, called its dominator tree. This structure is simple, elegant, and highly informative; all the bottlenecks and the effects of species removal are clearly traceable. While food web studies are mostly qualitative, in this paper the use of the dominator tree is extended to weighted food webs, in which link magnitude is specified. These structures were obtained from ecological flow networks. in eight of these food webs, the analysis consisted in removing links that were weaker than a threshold of magnitude and building the dominator tree associated to the remaining structure. By progressively increasing the threshold up to the value that would make the graph disconnected, we had the opportunity to investigate patterns of dominance as a function of link magnitude
Cities as ecosystems: Growth, development and implications for sustainability
No full textPrescriptions for a more sustainable society are usually piecemeal. They are inspired by single issue criteria, no matter if sustainability is, rather, a whole system trait as it pertains to growth and development, that are overall system attributes. In this paper urban sustainability is discussed in a whole system perspective using the ecosystem approach as a framework. This required that urban systems were described as flow networks and investigated through ecological network analysis. Three cities are discussed as a case study and their network representation concerned water flows that were identified knowing water exchanges between city components (i.e. sectors of human activity). Network analysis yielded system level indices that condense the complexity of the flow structure (representing system's metabolism) in a few measures that provide information on how systems grow and develop; as such they allow to explore sustainability at the whole system scale.For every system the present network is compared with an alternative scenario envisioned considering policies that foster sustainability. The results show that although all the alternative scenarios would improve sustainability through reducing water consumption, effects at the whole system level may diverge from the expectation. Because system sustainability depends on the balance between organization of flows (order and coherence of flows) and flexibility (redundancy of connections), network reshaping may bring about a reduction in both these fundamental properties, with negative effects on system's propensity to be sustainable.System level indices are holistic measures that unveil the relation between internal processes and whole system performance. Understanding this relation is crucial because the former are the target of environmental policies but sustainability, the objective of such policies, is an overall system trait. (C) 2012 Elsevier B.V. All rights reserved
Network science in ecology: the structure of ecological communities and the biodiversity question
No full textThe study of networks in ecology is rapidly expanding. Although network thinking is by no means new to ecologists, cross-fertilization from other fields, ranging from computer science to sociology, has recently furthered the field significantly. Here we examine some of the applications of network science to ecology with an emphasis on its potential to contribute to the preservation of biodiversity, an issue that has relevant social and policy implication. Two different forms in which ecological networks may appear are used: food webs and signed digraphs of dynamical systems. In the former, networks represent energy flow transfers form producers to consumers, while in the latter what is depicted is the effect that populations exert on each other.
The main objective is to enlighten how applying network science can contribute to some central questions concerning biodiversity such as the identification of keystone species, the response of population to environmental perturbations, the robustness or inertia of the system to external events in the form of loss of species and links and press perturbations that alter populations dynamics
- …
