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1. Generalized Lotka-Volterra Systems with Time Correlated Stochastic Interactions

Author

Suweis, Samir, Ferraro, Francesco, Azaele, Sandro, and Maritan, Amos

Subjects
Statistical Mechanics (cond-mat.stat-mech), Biological Physics (physics.bio-ph), FOS: Biological sciences, Populations and Evolution (q-bio.PE), FOS: Physical sciences, Physics - Biological Physics, Quantitative Biology - Populations and Evolution, Condensed Matter - Statistical Mechanics
Abstract

The dynamics of species communities are typically modelled considering fixed parameters for species interactions. The problem of over-parameterization that ensues when considering large communities has been overcome by sampling species interactions from a probability distribution. However, species interactions are not fixed in time, but they can change on a time scale comparable to population dynamics. Here we investigate the impact of time-dependent species interactions using the generalized Lotka-Volterra model, which serves as a paradigmatic theoretical framework in several scientific fields. In this work we model species interactions as stochastic colored noise. Assuming a large number of species and a steady state, we obtain analytical predictions for the species abundance distribution, which matches well empirical observations. In particular, our results suggest the absence of extinctions, unlike scenarios with fixed species interactions., Comment: 4 Figures

Published
2023
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2. Soft trade-offs and the stochastic emergence of diversification in E. coli evolution experiments

Author

López, Roberto Corral, Suweis, Samir, Azaele, Sandro, and Muñoz, Miguel A.

Subjects
Biological Physics (physics.bio-ph), FOS: Biological sciences, Populations and Evolution (q-bio.PE), FOS: Physical sciences, Physics - Biological Physics, Quantitative Biology - Populations and Evolution
Abstract

Laboratory experiments of bacterial colonies (e.g., \emph{Escherichia coli}) under well-controlled conditions often lead to evolutionary diversification in which (at least) two ecotypes, each one specialized in the consumption of a different set of metabolic resources, branch out from an initially monomorphic population. Empirical evidence suggests that, even under fixed and stable conditions, such an ``evolutionary branching'' occurs in a stochastic way, meaning that: (i) it is observed in a significant fraction, but not all, of the experimental repetitions, (ii) it may emerge at broadly diverse times, and (iii) the relative abundances of the resulting subpopulations are variable across experiments. Theoretical approaches shedding light on the possible emergence of evolutionary branching in this type of conditions have been previously developed within the theory of ``adaptive dynamics''. Such approaches are typically deterministic -- or incorporate at most demographic or finite-size fluctuations which become negligible for the extremely large populations of these experiments -- and, thus, do not permit to reproduce the empirically observed large degree of variability. Here, we make further progress and shed new light on the stochastic nature of evolutionary outcomes by introducing the idea of ``soft'' trade-offs (as opposed to ``hard'' ones). This introduces a natural new source of stochasticity which allows one to account for the empirically observed variability as well as to make predictions for the likelihood of evolutionary branching to be observed, thus helping to bridge the gap between theory and experiments.

Published
2023
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3. The architecture of information processing in biological systems

Author

Nicoletti, Giorgio, Bruzzone, Matteo, Suweis, Samir, Maschio, Marco Dal, and Busiello, Daniel Maria

Subjects
Chemical Physics (physics.chem-ph), Statistical Mechanics (cond-mat.stat-mech), Biological Physics (physics.bio-ph), Physics - Chemical Physics, FOS: Physical sciences, Physics - Biological Physics, Condensed Matter - Statistical Mechanics
Abstract

Biological systems process information at different scales and adapt to their changing environment. Informed both by experimental observations and theoretical constraints, we propose a chemical model for sensing that incorporates energy consumption, information storage, and negative feedback. We show that a biochemical architecture enclosing these minimal mechanisms leads to the emergence of dynamical memory and adaptation. Crucially, adaptation is associated with both an increase in the mutual information between external and internal variables and a reduction of dissipation of the internal chemical processes. By simultaneously minimizing energy consumption and maximizing information, we find that far-from-equilibrium sensing dominates in the low-noise regime. Our results, in principle, can be declined at different biological scales. We employ our model to shed light on large-scale neural adaptation in zebrafish larvae under repeated visual stimulation. We find striking similarities between predicted and observed behaviors, capturing the emergent adaptation of neural response. Our framework draws a path toward the unraveling of the essential ingredients that connect information processing, adaptation, and memory in biological systems.

Published
2023
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4. Genomic evidence for global ocean plankton biogeography shaped by large-scale current systems

Author

Richter, Daniel J., Watteaux, Romain, Vannier, Thomas, Leconte, Jade, Frémont, Paul, Reygondeau, Gabriel, Maillet, Nicolas, Henry, Nicolas, Benoit, Gaëtan, da Silva, Ophélie, Delmont, Tom O., Fernández-Guerra, Antonio, Suweis, Samir, Narci, Romain, Berney, Cedric, Eveillard, Damien, Gavory, Frederick, Guidi, Lionel, Labadie, Karine, Mahieu, Eric, Poulain, Julie, Romac, Sarah, Roux, Simon, Dimier, Céline, Kandels‐Lewis, Stefanie, Picheral, Marc, Searson, Sarah, Oceans, Tara, Pesant, Stéphane, Aury, Jean-Marc, Brum, Jennifer R., Lemaitre, Claire, Pelletier, Eric, Bork, Peer, Sunagawa, Shinichi, Lombard, Fabien, Karp-Boss, Lee, Bowler, Chris, Sullivan, Matthew B., Karsenti, Eric, Mariadassou, Mahendra, Probert, Ian, Peterlongo, Pierre, Wincker, Patrick, Vargas, Colomban de, Ribera d’Alcalà, Maurizio, Iudicone, Daniele, Jaillon, Olivier, Tara Oceans Coordinators, Centre National de la Recherche Scientifique (France), European Molecular Biology Laboratory, Centre National de Séquençage (France), National Fund for Scientific Research (Belgium), Stazione Zoologica Anton Dohrn, Università degli Studi di Milano, Université Paris Sciences & Lettres, Agence Nationale de la Recherche (France), National Science Foundation (US), Veolia Foundation, Région Bretagne, World Courier, Illumina, Cap L’Orient, Fondation EDF, Fondation pour la Recherche sur la Biodiversité, Fondation Prince Albert II de Monaco, Ministère de l'Europe et des Affaires étrangères (France), Adaptation et diversité en milieu marin (ADMM), Institut national des sciences de l'Univers (INSU - CNRS)-Station biologique de Roscoff (SBR), Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Stazione Zoologica Anton Dohrn (SZN), Institut méditerranéen d'océanologie (MIO), Institut de Recherche pour le Développement (IRD)-Aix Marseille Université (AMU)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Toulon (UTLN)-Centre National de la Recherche Scientifique (CNRS), Institut de Génomique d'Evry (IG), Université Paris-Saclay-Institut de Biologie François JACOB (JACOB), Direction de Recherche Fondamentale (CEA) (DRF (CEA)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Direction de Recherche Fondamentale (CEA) (DRF (CEA)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA), Genoscope - Centre national de séquençage [Evry] (GENOSCOPE), Université Paris-Saclay-Direction de Recherche Fondamentale (CEA) (DRF (CEA)), University of British Columbia (UBC), Hub Bioinformatique et Biostatistique - Bioinformatics and Biostatistics HUB, Institut Pasteur [Paris]-Centre National de la Recherche Scientifique (CNRS), Institut de Recherche en Informatique et Systèmes Aléatoires (IRISA), Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), Institut National des Sciences Appliquées (INSA)-Université de Rennes (UNIV-RENNES)-Institut National des Sciences Appliquées (INSA)-Université de Bretagne Sud (UBS)-École normale supérieure - Rennes (ENS Rennes)-Institut National de Recherche en Informatique et en Automatique (Inria)-CentraleSupélec-Centre National de la Recherche Scientifique (CNRS)-IMT Atlantique (IMT Atlantique), Institut Mines-Télécom [Paris] (IMT)-Institut Mines-Télécom [Paris] (IMT), Max Planck Institute for Marine Microbiology, Max-Planck-Gesellschaft, Dipartimento di Fisica e Astronomia 'Galileo Galilei', Università degli Studi di Padova = University of Padua (Unipd), Consorzio Nazionale Interuniversitario per le Scienze FIsiche della Materia (CNISM), Mathématiques et Informatique Appliquées du Génome à l'Environnement [Jouy-En-Josas] (MaIAGE), Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE), Station biologique de Roscoff (SBR), Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Laboratoire des Sciences du Numérique de Nantes (LS2N), Université de Nantes - UFR des Sciences et des Techniques (UN UFR ST), Université de Nantes (UN)-Université de Nantes (UN)-École Centrale de Nantes (ECN)-Centre National de la Recherche Scientifique (CNRS)-IMT Atlantique (IMT Atlantique), Combinatoire et Bioinformatique (LS2N - équipe COMBI), Institut Mines-Télécom [Paris] (IMT)-Institut Mines-Télécom [Paris] (IMT)-Université de Nantes - UFR des Sciences et des Techniques (UN UFR ST), Laboratoire d'océanographie de Villefranche (LOV), Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Institut de la Mer de Villefranche (IMEV), Institut de Biologie François JACOB (JACOB), Ohio State University [Columbus] (OSU), Institut de biologie de l'ENS Paris (IBENS), Département de Biologie - ENS Paris, École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut National de la Santé et de la Recherche Médicale (INSERM)-Centre National de la Recherche Scientifique (CNRS)-École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut National de la Santé et de la Recherche Médicale (INSERM)-Centre National de la Recherche Scientifique (CNRS)-Institut National de la Santé et de la Recherche Médicale (INSERM)-Centre National de la Recherche Scientifique (CNRS), Center for Marine Environmental Sciences [Bremen] (MARUM), Universität Bremen, Ecology and Evolutionary Biology [Tucson] (EEB), University of Arizona, Scalable, Optimized and Parallel Algorithms for Genomics (GenScale), Inria Rennes – Bretagne Atlantique, Institut National de Recherche en Informatique et en Automatique (Inria)-Institut National de Recherche en Informatique et en Automatique (Inria)-GESTION DES DONNÉES ET DE LA CONNAISSANCE (IRISA-D7), Institut Mines-Télécom [Paris] (IMT)-Institut Mines-Télécom [Paris] (IMT)-Université de Rennes 1 (UR1), Institut Mines-Télécom [Paris] (IMT)-Institut Mines-Télécom [Paris] (IMT)-Institut de Recherche en Informatique et Systèmes Aléatoires (IRISA), Institut National des Sciences Appliquées (INSA)-Université de Rennes (UNIV-RENNES)-Institut National des Sciences Appliquées (INSA)-Université de Bretagne Sud (UBS)-École normale supérieure - Rennes (ENS Rennes)-CentraleSupélec-Centre National de la Recherche Scientifique (CNRS)-IMT Atlantique (IMT Atlantique), European Molecular Biology Laboratory [Heidelberg] (EMBL), University of Maine, Institut Pasteur [Paris] (IP)-Centre National de la Recherche Scientifique (CNRS), Fédération de recherche de Roscoff (FR2424), Université de Rennes (UR)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), Institut National des Sciences Appliquées (INSA)-Institut National des Sciences Appliquées (INSA)-Université de Bretagne Sud (UBS)-École normale supérieure - Rennes (ENS Rennes)-Institut National de Recherche en Informatique et en Automatique (Inria)-CentraleSupélec-Centre National de la Recherche Scientifique (CNRS)-IMT Atlantique (IMT Atlantique), Institut Mines-Télécom [Paris] (IMT)-Institut Mines-Télécom [Paris] (IMT)-Université de Rennes (UR)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), Institut National des Sciences Appliquées (INSA)-Institut National des Sciences Appliquées (INSA)-Université de Bretagne Sud (UBS)-École normale supérieure - Rennes (ENS Rennes)-CentraleSupélec-Centre National de la Recherche Scientifique (CNRS)-IMT Atlantique (IMT Atlantique), French National Research Agency (ANR)HYDROGEN/ANR-14CE23-0001, National Science Foundation (NSF)OCE-1536989, OCE-1829831, Commissariat a l'Energie Atomique et aux Energies Alternatives, Graphene Flagship, European Project: 634486,H2020,H2020-BG-2014-2,INMARE(2015), European Project: 287589,EC:FP7:KBBE,FP7-OCEAN-2011,MICRO B3(2012), Adaptation et diversité en milieu marin (AD2M), Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay, Institut National des Sciences Appliquées (INSA)-Université de Rennes (UNIV-RENNES)-Institut National des Sciences Appliquées (INSA)-Université de Bretagne Sud (UBS)-École normale supérieure - Rennes (ENS Rennes)-Institut National de Recherche en Informatique et en Automatique (Inria)-CentraleSupélec-Centre National de la Recherche Scientifique (CNRS)-IMT Atlantique Bretagne-Pays de la Loire (IMT Atlantique), Universita degli Studi di Padova, Université de Nantes (UN)-Université de Nantes (UN)-École Centrale de Nantes (ECN)-Centre National de la Recherche Scientifique (CNRS)-IMT Atlantique Bretagne-Pays de la Loire (IMT Atlantique), Combinatoire et Bioinformatique (COMBI), Centre National de la Recherche Scientifique (CNRS)-Institut National de la Santé et de la Recherche Médicale (INSERM)-Département de Biologie - ENS Paris, École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut National de la Santé et de la Recherche Médicale (INSERM)-Centre National de la Recherche Scientifique (CNRS)-École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut National de la Santé et de la Recherche Médicale (INSERM)-Centre National de la Recherche Scientifique (CNRS), Institut National des Sciences Appliquées (INSA)-Université de Rennes (UNIV-RENNES)-Institut National des Sciences Appliquées (INSA)-Université de Bretagne Sud (UBS)-École normale supérieure - Rennes (ENS Rennes)-CentraleSupélec-Centre National de la Recherche Scientifique (CNRS)-IMT Atlantique Bretagne-Pays de la Loire (IMT Atlantique), Centre National de la Recherche Scientifique (CNRS)-Station biologique de Roscoff (SBR), Centre de Mathématiques et de Leurs Applications (CMLA), École normale supérieure - Cachan (ENS Cachan)-Centre National de la Recherche Scientifique (CNRS), Centre National de la Recherche Scientifique (CNRS)-Université de Toulon (UTLN)-Aix Marseille Université (AMU)-Institut de Recherche pour le Développement (IRD), Centre National de la Recherche Scientifique (CNRS)-Institut Pasteur [Paris], Infectiologie Santé Publique (ISP-311), Institut National de la Recherche Agronomique (INRA)-Université de Tours, Institut Pprime (PPRIME), Université de Poitiers-ENSMA-Centre National de la Recherche Scientifique (CNRS), Institut National de la Recherche Agronomique (INRA), Laboratoire d'Informatique de Nantes Atlantique (LINA), Mines Nantes (Mines Nantes)-Université de Nantes (UN)-Centre National de la Recherche Scientifique (CNRS), Institut de biologie de l'ENS Paris (UMR 8197/1024) (IBENS), École normale supérieure - Paris (ENS Paris)-École normale supérieure - Paris (ENS Paris)-Institut National de la Santé et de la Recherche Médicale (INSERM)-Centre National de la Recherche Scientifique (CNRS), Université de Bretagne Sud (UBS)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), Institut National des Sciences Appliquées (INSA)-Université de Rennes (UNIV-RENNES)-Institut National des Sciences Appliquées (INSA)-Université de Rennes (UNIV-RENNES)-Institut National de Recherche en Informatique et en Automatique (Inria)-École normale supérieure - Rennes (ENS Rennes)-Centre National de la Recherche Scientifique (CNRS)-Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-CentraleSupélec-IMT Atlantique Bretagne-Pays de la Loire (IMT Atlantique), IMT Atlantique Bretagne-Pays de la Loire (IMT Atlantique), Université de Nantes (UN)-Université de Nantes (UN)-École Centrale de Nantes (ECN)-Centre National de la Recherche Scientifique (CNRS), Institut Mines-Télécom [Paris] (IMT)-Institut Mines-Télécom [Paris] (IMT)-Université de Bretagne Sud (UBS)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), and Institut National des Sciences Appliquées (INSA)-Université de Rennes (UNIV-RENNES)-Institut National des Sciences Appliquées (INSA)-Université de Rennes (UNIV-RENNES)-École normale supérieure - Rennes (ENS Rennes)-Centre National de la Recherche Scientifique (CNRS)-Université de Rennes 1 (UR1)

Subjects
010504 meteorology & atmospheric sciences, Biogeography, Oceans and Seas, Context (language use), 01 natural sciences, General Biochemistry, Genetics and Molecular Biology, 03 medical and health sciences, plankton biogeography, genomics, Ecosystem, genetics, 14. Life underwater, microbial oceanography, 030304 developmental biology, 0105 earth and related environmental sciences, Seascape, [SDV.EE]Life Sciences [q-bio]/Ecology, environment, 0303 health sciences, metagenomics, General Immunology and Microbiology, Geography, General Neuroscience, Ocean current, fungi, Community structure, General Medicine, 15. Life on land, Plankton, Oceanography, 13. Climate action, Metagenomics, metabarcoding, ecology, [INFO.INFO-BI]Computer Science [cs]/Bioinformatics [q-bio.QM]
Abstract

Biogeographical studies have traditionally focused on readily visible organisms, but recent technological advances are enabling analyses of the large-scale distribution of microscopic organisms, whose biogeographical patterns have long been debated. Here we assessed the global structure of plankton geography and its relation to the biological, chemical, and physical context of the ocean (the ‘seascape’) by analyzing metagenomes of plankton communities sampled across oceans during the Tara Oceans expedition, in light of environmental data and ocean current transport. Using a consistent approach across organismal sizes that provides unprecedented resolution to measure changes in genomic composition between communities, we report a pan-ocean, size-dependent plankton biogeography overlying regional heterogeneity. We found robust evidence for a basin-scale impact of transport by ocean currents on plankton biogeography, and on a characteristic timescale of community dynamics going beyond simple seasonality or life history transitions of plankton., We thank the commitment of the following people and sponsors who made this expedition possible: CNRS (in particular Groupement de Recherche GDR3280), European Molecular Biology Laboratory (EMBL), Genoscope/CEA, Fund for Scientific Research – Flanders, VIB, Stazione Zoologica Anton Dohrn, UNIMIB, Paris Sciences et Lettres (PSL) Research University (ANR-11-IDEX-0001–02), the French Government ANR (projects FRANCE GENOMIQUE/ANR-10-INBS-09, MEMO LIFE/ANR-10-LABX-54, POSEIDON/ANR-09-BLAN-0348, PROMETHEUS/ANR-09-PCS-GENM-217, MAPPI/ANR-2010-COSI-004, TARA-GIRUS/ANR-09-PCS-GENM-218), US NSF grant DEB-1031049, FWO, BIO5, Biosphere 2, Agnès b., the Veolia Environment Foundation, Région Bretagne, World Courier, Illumina, Cap L’Orient, the EDF Foundation EDF Diversiterre, FRB, the Prince Albert II de Monaco Foundation, Etienne Bourgois, the Tara schooner and its captain and crew. We thank MERCATOR-CORIOLIS and ACRI-ST for providing daily satellite data during the expedition. The bulk of genomic computations were performed using the Airain HPC machine provided through GENCI- [TGCC/CINES/IDRIS] (grants t2011076389, t2012076389, t2013036389, t2014036389, t2015036389 and t2016036389). We are also grateful to the French Ministry of Foreign Affairs for supporting the expedition and to the countries who granted us sampling permissions.

Published
2022

5. Pairing statistics and melting of random DNA oligomers: Finding your partner in superdiverse environments

Author

Leo, Simone Di, Marni, Stefano, Plata Ramos, Carlos Alberto, Fraccia, Tommaso P., Smith, Gregory P., Maritan, Amos, Suweis, Samir, Bellini, Tommaso, and Universidad de Sevilla. Departamento de Física Atómica, Molecular y Nuclear

Abstract

Understanding of the pairing statistics in solutions populated by a large number of distinct solute species with mutual interactions is a challenging topic, relevant in modeling the complexity of real biological systems. Here we describe, both experimentally and theoretically, the formation of duplexes in a solution of random-sequence DNA (rsDNA) oligomers of length L = 8, 12, 20 nucleotides. rsDNA solutions are formed by 4L distinct molecular species, leading to a variety of pairing motifs that depend on sequence complementarity and range from strongly bound, fully paired defectless helices to weakly interacting mismatched duplexes. Experiments and theory coherently combine revealing a hybridization statistics characterized by a prevalence of partially defected duplexes, with a distribution of type and number of pairing errors that depends on temperature. We find that despite the enormous multitude of inter-strand interactions, defectless duplexes are formed, involving a fraction up to 15% of the rsDNA chains at the lowest temperatures. Experiments and theory are limited here to equilibrium conditions.

Published
2022

6. The emergence of cooperation from shared goals in the Systemic Sustainability Game of common pool resources

Author

Tu, Chengyi, DOdorico, Paolo, Li, Zhe, and Suweis, Samir

Subjects
FOS: Economics and business, Economics - Theoretical Economics, Theoretical Economics (econ.TH)
Abstract

The sustainable use of common-pool resources (CPRs) is a major environmental governance challenge because of their possible over-exploitation. Research in this field has overlooked the feedback between user decisions and resource dynamics. Here we develop an online game to perform a set of experiments in which users of the same CPR decide on their individual harvesting rates, which in turn depend on the resource dynamics. We show that, if users share common goals, a high level of self-organized cooperation emerges, leading to long-term resource sustainability. Otherwise, selfish/individualistic behaviors lead to resource depletion ("Tragedy of the Commons"). To explain these results, we develop an analytical model of coupled resource-decision dynamics based on optimal control theory and show how this framework reproduces the empirical results.

Published
2021
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7. Virtual water controlled demographic growth of nations

Author

Suweis, Samir, Rinaldo, Andrea, Maritan, Amos, and D'Odorico, Paolo

Subjects
Physics - Geophysics, Physics - Physics and Society, Physics - Data Analysis, Statistics and Probability, FOS: Physical sciences, Physics and Society (physics.soc-ph), Data Analysis, Statistics and Probability (physics.data-an), Geophysics (physics.geo-ph)
Abstract

Population growth is in general constrained by food production, which in turn depends on the access to water resources. At a country level, some populations use more water than they control because of their ability to import food and the virtual water required for its production. Here, we investigate the dependence of demographic growth on available water resources for exporting and importing nations. By quantifying the carrying capacity of nations based on calculations of the virtual water available through the food trade network, we point to the existence of a global water unbalance. We suggest that current export rates will not be maintained and consequently we question the long-run sustainability of the food trade system as a whole. Water rich regions are likely to soon reduce the amount of virtual water they export, thus leaving import-dependent regions without enough water to sustain their populations. We also investigate the potential impact of possible scenarios that might mitigate these effects through (1) cooperative interactions among nations whereby water rich countries maintain a tiny fraction of their food production available for export; (2) changes in consumption patterns; and (3) a positive feedback between demographic growth and technological innovations. We find that these strategies may indeed reduce the vulnerability of water-controlled societies., Comment: 11 pages, 3 figures

Published
2013
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8. Water for food: The global virtual water trade network

Author

Konar, M., Dalin, C., Suweis, SAMIR SIMON, Hanasaki, N., Rinaldo, Andrea, and Rodriguez Iturbe, I.

Subjects
Integrated Model, Flows, Products, Complex Networks, Resources, Scale
Abstract

We present a novel conceptual framework and methodology for studying virtual water trade. We utilize complex network theory to analyze the structure of the global virtual water trade associated with the international food trade. In the global virtual water trade network, the nations that participate in the international food trade correspond to the nodes, and the links represent the flows of virtual water associated with the trade of food from the country of export to the country of import. We find that the number of trade connections follows an exponential distribution, except for the case of import trade relationships, while the volume of water that each nation trades compares well with a stretched exponential distribution, indicating high heterogeneity of flows between nations. There is a power law relationship between the volume of virtual water traded and the number of trade connections of each nation. Highly connected nations are preferentially linked to poorly connected nations and exhibit low levels of clustering. However, when the volume of virtual water traded is taken into account, this structure breaks down. This indicates a global hierarchy, in which nations that trade large volumes of water are more likely to link to and cluster with other nations that trade large volumes of water, particularly when the direction of trade is considered. Nations that play a critical role in maintaining the global network architecture are highlighted. Our analysis provides the necessary framework for the development of a model of global virtual water trade aimed at applications ranging from network optimization to climate change impact evaluations.

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