1. Punish, but not too hard: how costly punishment spreads in the spatial public goods gameDirk Helbing, Attila Szolnoki, Matjaž Perc, György Szabó, 2010, izvirni znanstveni članek Opis: We study the evolution of cooperation in spatial public goods games where, besides the classical strategies of cooperation (C) and defection (D), we consider punishing cooperators (PC) or punishing defectors (PD) as an additional strategy. Using a minimalist modeling approach, our goal is to separately clarify and identify the consequences of the two punishing strategies. Since punishment is costly, punishing strategies lose the evolutionary competition in case of well-mixed interactions. When spatial interactions are taken into account, however, the outcome can be strikingly different, and cooperation may spread. The underlying mechanism depends on the character of the punishment strategy. In the case of cooperating punishers,increasing the fine results in a rising cooperation level. In contrast, in the presence of the PD strategy, the phase diagram exhibits a reentrant transition as the fine is increased. Accordingly, the level of cooperation shows a non-monotonous dependence on the fine. Remarkably, punishing strategies can spread in both cases, but based on largely different mechanisms, which depend on the cooperativeness (or not) of punishers.
Ključne besede: evolutionary game theory, public goods, spatial games, punishment, social systems, moral
Objavljeno v DKUM: 03.07.2017; Ogledov: 1855; Prenosov: 406
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2. Evolution of cooperation on scale-free networks subject to error and attackMatjaž Perc, 2009, izvirni znanstveni članek Opis: We study the evolution of cooperation in the prisoner's dilemma and the snowdrift game on scale-free networks that are subjected to intentional and random removal of vertices. We show that, irrespective of the game type, cooperation on scale-free networks is extremely robust against random deletionof vertices, but declines quickly if vertices with the maximal degree are targeted. In particular, attack tolerance is lowest if the temptation to defect is largest, whereby a small fraction of removed vertices suffices to decimate cooperators. The decline of cooperation can be directly linked to the decrease of heterogeneity of scale-free networks that sets in due to the removal of high degree vertices. We conclude that the evolution of cooperation is characterized by similar attack and error tolerance as was previously reported for information readiness and spread of viruses on scale-free networks.
Ključne besede: evolutionary game theory, social dilemma, spatial games, complex networks
Objavljeno v DKUM: 30.06.2017; Ogledov: 1622; Prenosov: 382
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3. Emergence of target waves in paced populations of cyclically competing speciesLuo-Luo Jiang, Tao Zhou, Matjaž Perc, Xin Huang, Bing-Hong Wang, 2009, izvirni znanstveni članek Opis: We investigate the emergence of target waves in a cyclic predator-prey model incorporating a periodic current of the three competing species in a small area situated at the center of a square lattice. The periodic current acts as a pacemaker, trying to impose its rhythm on the overall spatiotemporal evolution of the three species. We show that the pacemaker is able to nucleate target waves that eventually spread across the whole population, whereby three routes leading to this phenomenon can be distinguished depending on the mobility of the three species and the oscillation period of the localized current. First, target waves can emerge due to the synchronization between the periodic current and oscillations of the density of the three species on the spatial grid. The second route is similar to the first, the difference being that the synchronization sets in only intermittently. Finally, the third route toward target waves is realized when the frequency of the pacemaker is much higher than that characterizing the oscillations of the overall density of the three species. By considering the mobility and frequency of the current as variable parameters, we thus provide insights into the mechanisms of pattern formation resulting from the interplay between local and global dynamics in systems governed by cyclically competing species.
Ključne besede: cyclical interactions, target waves, spatial games, diversity
Objavljeno v DKUM: 30.06.2017; Ogledov: 1555; Prenosov: 399
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4. Emergence of multilevel selection in the prisoner's dilemma game on coevolving random networksAttila Szolnoki, Matjaž Perc, 2009, izvirni znanstveni članek Opis: We study the evolution of cooperation in the prisoner's dilemma game, whereby a coevolutionary rule is introduced that molds the random topology of the interaction network in two ways. First, existing links are deleted whenever a player adopts a new strategy or its degree exceeds a threshold value; second, new links are added randomly after a given number of game iterations. These coevolutionary processes correspond to the generic formation of new links and deletion of existing links that, especially in human societies, appear frequently as a consequence of ongoing socialization, change of lifestyle or death. Due to the counteraction of deletions and additions of links the initial heterogeneity of the interaction network is qualitatively preserved, and thus cannot be held responsible for the observed promotion of cooperation. Indeed, the coevolutionary rule evokes the spontaneous emergence of a powerful multilevel selection mechanism, which despite the sustained random topology of the evolving network, maintains cooperation across the whole span of defection temptation values.
Ključne besede: evolutionary game theory, prisoner's dilemma, spatial games, coevolution, social systems
Objavljeno v DKUM: 30.06.2017; Ogledov: 1738; Prenosov: 423
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5. Coevolution of teaching activity promotes cooperationAttila Szolnoki, Matjaž Perc, 2008, izvirni znanstveni članek Opis: Evolutionary games are studied where the teaching activity of players can evolve in time. Initially all players following either the cooperative or defecting strategy are distributed on a square lattice. The rate of strategy adoption is determined by the payoff difference and a teaching activity characterizing the donor's capability to enforce its strategy on the opponent. Each successful strategy adoption process is accompanied by an increase in the donor's teaching activity. By applying an optimum value of the increment, this simple mechanism spontaneously creates relevant inhomogeneities in the teaching activities that support the maintenance of cooperation for both the prisoner's dilemma and the snowdrift game.
Ključne besede: evolutionary game theory, prisoner's dilemma, spatial games, snowdrift game, coevolution
Objavljeno v DKUM: 30.06.2017; Ogledov: 1370; Prenosov: 485
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6. Heterogeneous aspirations promote cooperation in the prisoner's dilemma gameMatjaž Perc, Zhen Wang, 2010, izvirni znanstveni članek Opis: To be the fittest is central to proliferation in evolutionary games. Individuals thus adopt the strategies of better performing players in the hopeof successful reproduction. In structured populations the array of those that are eligible to act as strategy sources is bounded to the immediate neighbors of each individual. But which one of these strategy sources should potentially be copied? Previous research dealt with this question either by selecting the fittest or by selecting one player uniformly at random. Here we introduce a parameter that interpolates between these two extreme options. Setting equal to zero returns the random selection of the opponent, while positive favor the fitter players. In addition, we divide the population intotwo groups. Players from group select their opponents as dictated by the parameter , while players from group do so randomly irrespective of . We denote the fraction of players contained in groups and by and , respectively. The two parameters and allow us to analyze in detail how aspirations in the context of the prisoner's dilemma game influence the evolution of cooperation. We find that for sufficiently positive values of there exist a robust intermediate for which cooperation thrives best. The robustness of this observation is tested against different levels of uncertainty in the strategy adoption process and for different interaction networks. We also provide complete phase diagrams depicting the dependence of the impact of and for different values of , and contrast the validity of ourconclusions by means of an alternative model where individual aspiration levels are subject to evolution as well. Our study indicates that heterogeneity in aspirations may be key for the sustainability of cooperation in structured populations.
Ključne besede: evolutionary game theory, prisoner's dilemma, spatial games, aspirations, social systems, physics and society
Objavljeno v DKUM: 19.06.2017; Ogledov: 1476; Prenosov: 394
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7. Evolutionary establishment of moral and double moral standards through spatial interactionsDirk Helbing, Attila Szolnoki, Matjaž Perc, György Szabó, 2010, izvirni znanstveni članek Opis: Situations where individuals have to contribute to joint efforts or share scarce resources are ubiquitous. Yet, without proper mechanisms to ensure cooperation, the evolutionary pressure to maximize individual success tends to create a tragedy of the commons (such as over-fishing or the destruction of our environment). This contribution addresses a number of related puzzles of human behavior with an evolutionary game theoretical approach as it has been successfully used to explain the behavior of other biological species many times, from bacteria to vertebrates. Our agent-based model distinguishes individuals applying four different behavioral strategies: non-cooperative individuals ('defectors'), cooperative individuals abstaining from punishment efforts (called 'cooperators' or 'second-order free-riders'), cooperators who punish non-cooperative behavior ('moralists'), and defectors, who punish otherdefectors despite being non-cooperative themselves ('immoralists'). By considering spatial interactions with neighboring individuals, our model reveals several interesting effects: First, moralists can fully eliminate cooperators. This spreading of punishing behavior requires a segregation of behavioral strategies and solves the 'second-order free-rider problem'. Second, the system behavior changes its character significantly even after very long times ('who laughs last laughs best effect'). Third, the presence of a number of defectors can largely accelerate the victory of moralists over non-punishing cooperators. Fourth, in order to succeed, moralists may profit from immoralists in a way that appears like an 'unholy collaboration'. Our findings suggest that the consideration of punishment strategies allows one to understand the establishment and spreading of 'moral behavior' by means of game-theoretical concepts. This demonstrates that quantitative biological modeling approaches are powerful even in domains that have been addressed with non-mathematical concepts so far. The complex dynamics of certain social behaviors become understandable as the result of an evolutionary competition between different behavioral strategies.
Ključne besede: evolutionary game theory, social dilemmas, spatial games, moral, cooperation
Objavljeno v DKUM: 16.06.2017; Ogledov: 1463; Prenosov: 415
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8. Uncertainties facilitate aggressive behavior in a spatial hawk-dove gameMatjaž Perc, 2007, izvirni znanstveni članek Opis: We study effects of additive spatiotemporal random variations, introduced to the payoffs of a spatial hawk-dove game, on the evolution of the reconciliatory and the aggressive strategy. We show that uncertainties facilitate aggressive behavior for a broad range of resource values. In particular, aggressors thrive best if stochastic influences are of the order of magnitude of deterministic payoff values. We argue that random payoff variations are potent and plausible promoters of aggressive behavior in human as well as animal societies if only the hawk-dove game payoff ranking applies.
Ključne besede: evolutionary game theory, hawk-dove game, noise, spatial games
Objavljeno v DKUM: 31.05.2012; Ogledov: 2231; Prenosov: 67
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