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Nicolis, Stamatios C.
Publications (10 of 10) Show all publications
Nicolis, G. & Nicolis, S. C. (2015). Probabilistic Network Approach to Decision-Making. Open systems & information dynamics, 22(2), Article ID 1550012.
Open this publication in new window or tab >>Probabilistic Network Approach to Decision-Making
2015 (English)In: Open systems & information dynamics, ISSN 1230-1612, E-ISSN 1573-1324, Vol. 22, no 2, article id 1550012Article in journal (Refereed) Published
Abstract [en]

A probabilistic approach to decision-making is developed in which the states of the underlying stochastic process, assumed to be of the Markov type, represent the competing options. The principal parameters determining the dominance of a particular option versus the others are identified and the transduction of information associated to the transitions between states is quantified using a set of entropy-like quantities.

National Category
Probability Theory and Statistics
Identifiers
urn:nbn:se:uu:diva-260736 (URN)10.1142/S1230161215500122 (DOI)000358260000005 ()
Funder
EU, European Research Council, IDCAB 220/104702003
Available from: 2015-08-24 Created: 2015-08-24 Last updated: 2017-12-04Bibliographically approved
Ranganathan, S., Nicolis, S. C., Spaiser, V. & Sumpter, D. J. (2015). Understanding Democracy and Development Traps Using a Data-Driven Approach. Big Data, 3(1), 22-33
Open this publication in new window or tab >>Understanding Democracy and Development Traps Using a Data-Driven Approach
2015 (English)In: Big Data, ISSN 2167-6461, Vol. 3, no 1, p. 22-33Article in journal (Refereed) Published
Abstract [en]

Methods from machine learning and data science are becoming increasingly important in the social sciences, providing powerful new ways of identifying statistical relationships in large data sets. However, these relationships do not necessarily offer an understanding of the processes underlying the data. To address this problem, we have developed a method for fitting nonlinear dynamical systems models to data related to social change. Here, we use this method to investigate how countries become trapped at low levels of socioeconomic development. We identify two types of traps. The first is a democracy trap, where countries with low levels of economic growth and/or citizen education fail to develop democracy. The second trap is in terms of cultural values, where countries with low levels of democracy and/or life expectancy fail to develop emancipative values. We show that many key developing countries, including India and Egypt, lie near the border of these development traps, and we investigate the time taken for these nations to transition toward higher democracy and socioeconomic well-being.

National Category
Computer and Information Sciences Political Science
Identifiers
urn:nbn:se:uu:diva-261283 (URN)10.1089/big.2014.0066 (DOI)000355563100003 ()
Available from: 2015-09-01 Created: 2015-09-01 Last updated: 2018-01-11Bibliographically approved
Arganda, S., Nicolis, S. C., Perochain, A., Pechabadens, C., Latil, G. & Dussutour, A. (2014). Collective choice in ants: The role of protein and carbohydrates ratios. Journal of insect physiology, 69, 19-26
Open this publication in new window or tab >>Collective choice in ants: The role of protein and carbohydrates ratios
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2014 (English)In: Journal of insect physiology, ISSN 0022-1910, E-ISSN 1879-1611, Vol. 69, p. 19-26Article in journal (Refereed) Published
Abstract [en]

In a foraging context, social insects make collective decisions from individuals responding to local information. When faced with foods varying in quality, ants are known to be able to select the best food source using pheromone trails. Until now, studies investigating collective decisions have focused on single nutrients, mostly carbohydrates. In the environment, the foods available are a complex mixture and are composed of various nutrients, available in different forms. In this paper, we explore the effect of protein to carbohydrate ratio on ants' ability to detect and choose between foods with different protein characteristics (free amino acids or whole proteins). In a two-choice set up, Argentine ants Linepithema humile were presented with two artificial foods containing either whole protein or amino acids in two different dietary conditions: high protein food or high carbohydrate food. At the collective level, when ants were faced with high carbohydrate foods, they did not show a preference between free amino acids or whole proteins, while a preference for free amino acids emerged when choosing between high protein foods. At the individual level, the probability of feeding was higher for high carbohydrates food and for foods containing free amino acids. Two mathematical models were developed to evaluate the importance of feeding probability in collective food selection. A first model in which a forager deposits pheromone only after feeding, and a second model in which a forager always deposits pheromone, but with greater intensity after feeding. Both models were able to predict free amino acid selection, however the second one was better able to reproduce the experimental results suggesting that modulating trail strength according to feeding probability is likely the mechanism explaining amino acid preference at a collective level in Argentine ants.

Keywords
Collective decision, Nutrition, Protein, Amino acids, Foraging, Recruitment, Ants
National Category
Zoology
Identifiers
urn:nbn:se:uu:diva-237320 (URN)10.1016/j.jinsphys.2014.04.002 (DOI)000343341200004 ()24751909 (PubMedID)
Available from: 2014-12-01 Created: 2014-12-01 Last updated: 2017-12-05Bibliographically approved
Nicolis, S. C. & Nicolis, G. (2014). Dynamics of Collective Decisions in a Time-Dependent Environment. International Journal of Bifurcation and Chaos in Applied Sciences and Engineering, 24(8), 1440010
Open this publication in new window or tab >>Dynamics of Collective Decisions in a Time-Dependent Environment
2014 (English)In: International Journal of Bifurcation and Chaos in Applied Sciences and Engineering, ISSN 0218-1274, Vol. 24, no 8, p. 1440010-Article in journal (Refereed) Published
Abstract [en]

The field of dynamical systems had been revolutionized by the seminal work of Leonid Shil'nikov. As a tribute to his genius we analyze in this paper the response of dynamical systems to systematic variations of a control parameter in time, using a normal form approach. Explicit expressions of the normal forms and of their parameter dependences are derived for a class of systems possessing multiple steady-states associated to collective choices between several options in group-living organisms, giving rise to bifurcations of the pitchfork and of the limit point type. Depending on the conditions, delays in the transitions between states, stabilization of metastable states, or on the contrary enhancement of the choice of the most rewarding option induced by the time dependence of the parameter are identified.

Keywords
Normal forms, dynamical bifurcations, collective behavior, mathematical biology
National Category
Mathematics
Identifiers
urn:nbn:se:uu:diva-233604 (URN)10.1142/S0218127414400100 (DOI)000341494900011 ()
Available from: 2014-10-09 Created: 2014-10-07 Last updated: 2017-12-05Bibliographically approved
Zabzina, N., Dussutour, A., Mann, R. P., Sumpter, D. J. T. & Nicolis, S. C. (2014). Symmetry Restoring Bifurcation in Collective Decision-Making. PloS Computational Biology, 10(12), e1003960
Open this publication in new window or tab >>Symmetry Restoring Bifurcation in Collective Decision-Making
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2014 (English)In: PloS Computational Biology, ISSN 1553-734X, E-ISSN 1553-7358, Vol. 10, no 12, p. e1003960-Article in journal (Refereed) Published
Abstract [en]

How social groups and organisms decide between alternative feeding sites or shelters has been extensively studied both experimentally and theoretically. One key result is the existence of a symmetry-breaking bifurcation at a critical system size, where there is a switch from evenly distributed exploitation of all options to a focussed exploitation of just one. Here we present a decision-making model in which symmetry-breaking is followed by a symmetry restoring bifurcation, whereby very large systems return to an even distribution of exploitation amongst options. The model assumes local positive feedback, coupled with a negative feedback regulating the flow toward the feeding sites. We show that the model is consistent with three different strains of the slime mold Physarum polycephalum, choosing between two feeding sites. We argue that this combination of feedbacks could allow collective foraging organisms to react flexibly in a dynamic environment.

National Category
Mathematical Analysis
Identifiers
urn:nbn:se:uu:diva-312747 (URN)
Funder
EU, European Research Council, IDCAB 220/104702003
Available from: 2017-01-12 Created: 2017-01-12 Last updated: 2017-11-29
Zabzina, N., Dussutour, A., Mann, R. P., Sumpter, D. J. T. & Nicolis, S. C. (2014). Symmetry Restoring Bifurcation in Collective Decision-Making. PloS Computational Biology, 10(12), e1003960
Open this publication in new window or tab >>Symmetry Restoring Bifurcation in Collective Decision-Making
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2014 (English)In: PloS Computational Biology, ISSN 1553-734X, E-ISSN 1553-7358, Vol. 10, no 12, p. e1003960-Article in journal (Refereed) Published
Abstract [en]

How social groups and organisms decide between alternative feeding sites or shelters has been extensively studied both experimentally and theoretically. One key result is the existence of a symmetry-breaking bifurcation at a critical system size, where there is a switch from evenly distributed exploitation of all options to a focussed exploitation of just one. Here we present a decision-making model in which symmetry-breaking is followed by a symmetry restoring bifurcation, whereby very large systems return to an even distribution of exploitation amongst options. The model assumes local positive feedback, coupled with a negative feedback regulating the flow toward the feeding sites. We show that the model is consistent with three different strains of the slime mold Physarum polycephalum, choosing between two feeding sites. We argue that this combination of feedbacks could allow collective foraging organisms to react flexibly in a dynamic environment.

National Category
Mathematical Analysis
Identifiers
urn:nbn:se:uu:diva-243062 (URN)10.1371/journal.pcbi.1003960 (DOI)000346656700020 ()
Funder
EU, European Research Council, IDCAB 220/104702003
Available from: 2015-02-09 Created: 2015-02-04 Last updated: 2017-12-04Bibliographically approved
Dussutour, A. & Nicolis, S. C. (2013). Flexibility in collective decision-making by ant colonies: Tracking food across space and time. Chaos, Solitons & Fractals, 50(SI), 32-38
Open this publication in new window or tab >>Flexibility in collective decision-making by ant colonies: Tracking food across space and time
2013 (English)In: Chaos, Solitons & Fractals, ISSN 0960-0779, E-ISSN 1873-2887, Vol. 50, no SI, p. 32-38Article in journal (Refereed) Published
Abstract [en]

Deciding which of many available resources to exploit is a problem faced by a range of decentralized biological systems. For example, ants are able to choose between food sources that vary in quality using a chemical trail. This communication system characterized by a strong positive feedback allows a rapid transfer of information and the selection of the best food source. This is true in static environment, where a single, unchanging solution exists. In dynamic environments however such recruitment often 'lock' groups into suboptimal decisions, preventing a response to changes in available resources. Here, we investigate decision-making in a dynamic environment for the greenhead ants (Rhytidoponera metallica) which use a non-chemical recruitment. To experimentally test our study species' ability to adapt to changes in their foraging environment, we offered three feeders that changed in quality. At any given time, only one feeder provided high quality food, while the others provided low quality food. Every two hours, the quality of the feeders changed such that the previously high quality feeder became a low quality feeder, and vice versa. We showed that ants were able to track changes in food quality across space and time. By coupling behavioral observations to computer simulations, we demonstrate that selection of food sources relies uniquely on a retention effect of feeding individuals on newcomers without comparison between available opportunities. The elegance of these parsimonious foraging systems is that the collective decision arises from the perception of conspecifics without the need for a leader having a synoptic overall view of the situation and knowing all the available options.

National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-201236 (URN)10.1016/j.chaos.2013.02.004 (DOI)000318208300004 ()
Note

Both authors contributed equally.

Available from: 2013-06-10 Created: 2013-06-10 Last updated: 2017-12-06Bibliographically approved
Nicolis, S. C., Fernandez, J., Perez-Penichet, C., Noda, C., Tejera, F., Ramos, O., . . . Altshuler, E. (2013). Foraging at the Edge of Chaos: Internal Clock versus External Forcing. Physical Review Letters, 110(26), 268104
Open this publication in new window or tab >>Foraging at the Edge of Chaos: Internal Clock versus External Forcing
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2013 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 110, no 26, p. 268104-Article in journal (Refereed) Published
Abstract [en]

Activity rhythms in animal groups arise both from external changes in the environment, as well as from internal group dynamics. These cycles are reminiscent of physical and chemical systems with quasiperiodic and even chaotic behavior resulting from "autocatalytic'' mechanisms. We use nonlinear differential equations to model how the coupling between the self-excitatory interactions of individuals and external forcing can produce four different types of activity rhythms: quasiperiodic, chaotic, phase locked, and displaying over or under shooting. At the transition between quasiperiodic and chaotic regimes, activity cycles are asymmetrical, with rapid activity increases and slower decreases and a phase shift between external forcing and activity. We find similar activity patterns in ant colonies in response to varying temperature during the day. Thus foraging ants operate in a region of quasiperiodicity close to a cascade of transitions leading to chaos. The model suggests that a wide range of temporal structures and irregularities seen in the activity of animal and human groups might be accounted for by the coupling between collectively generated internal clocks and external forcings.

National Category
Mathematics
Identifiers
urn:nbn:se:uu:diva-204797 (URN)10.1103/PhysRevLett.110.268104 (DOI)000320999200005 ()
Available from: 2013-08-15 Created: 2013-08-12 Last updated: 2017-12-06Bibliographically approved
Perna, A., Granovskiy, B., Garnier, S., Nicolis, S. C., Labédan, M., Theraulaz, G., . . . Sumpter, D. J. T. (2012). Individual Rules for Trail Pattern Formation in Argentine Ants (Linepithema humile). PloS Computational Biology, 8(7), e1002592
Open this publication in new window or tab >>Individual Rules for Trail Pattern Formation in Argentine Ants (Linepithema humile)
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2012 (English)In: PloS Computational Biology, ISSN 1553-734X, E-ISSN 1553-7358, Vol. 8, no 7, p. e1002592-Article in journal (Refereed) Published
Abstract [en]

Many ant species produce large dendritic networks of trails around their nest. These networks result from self-organized feedback mechanisms: ants leave small amounts of a chemical -a pheromone- as they move across space. In turn, they are attracted by this same pheromone so that eventually a trail is formed. In our study, we introduce a new image analysis technique to estimate the concentrations of pheromone directly on the trails. In this way, we can characterise the ingredients of the feedback loop that ultimately leads to the formation of trails. We show that the response to pheromone concentrations is linear: an ant will turn to the left with frequency proportional to the difference between the pheromone concentrations on its left and right sides. Such a linear individual response was rejected by previous literature, as it would be incompatible with the results of a large number of experiments: trails can only be reinforced if the ants have a disproportionally higher probability to select the trail with higher pheromone concentration. However, we show that the required non-linearity does not reside in the perceptual response of the ants, but in the noise associated with their movement.

National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-180968 (URN)10.1371/journal.pcbi.1002592 (DOI)000306842200017 ()
Available from: 2012-09-14 Created: 2012-09-14 Last updated: 2017-12-07Bibliographically approved
Nicolis, S. C. & Sumpter, D. J. T. (2011). A dynamical approach to stock market fluctuations. International Journal of Bifurcation and Chaos in Applied Sciences and Engineering, 21(12), 3557-3564
Open this publication in new window or tab >>A dynamical approach to stock market fluctuations
2011 (English)In: International Journal of Bifurcation and Chaos in Applied Sciences and Engineering, ISSN 0218-1274, Vol. 21, no 12, p. 3557-3564Article in journal (Refereed) Published
Abstract [en]

The recent turbulence on the world's stock markets has reinvigorated the attack on classical economic models of stock market fluctuations. The key problem is determining a dynamic model, which is consistent with observed fluctuations and which reflects investor behavior. Here, we use a novel equation-free approach developed in nonlinear dynamics literature to identify the salient statistical features of fluctuations of the Dow Jones Industrial Average over the past 80 years. We then develop a minimal dynamical model in the form of a stochastic differential equation involving both additive and multiplicative system-noise couplings, which captures these features and whose parameterization on a time scale of days can be used to capture market distributions up to a time scale of months. The terms in the model can be directly linked to "herding" behavior on the part of traders. However, we show that parameters in this model have changed over a number of decades producing different market regimes. This result partially explains how, during some periods of history, "classic" economic models may work well and at other periods "econo-physics" models prove better.

Keywords
Econophysics, stochastic processes, extreme events
National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-169985 (URN)10.1142/S0218127411030726 (DOI)000300016000011 ()
Available from: 2012-03-08 Created: 2012-03-07 Last updated: 2017-12-07Bibliographically approved
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