29 research outputs found
Cooperation in public goods games: stay, but not for too long
Cooperation in repeated public goods game is hardly achieved, unless
contingent behavior is present. Surely, if mechanisms promoting positive
assortment between cooperators are present, then cooperators may beat
defectors, because cooperators would collect greater payoffs. In the context of
evolutionary game theory, individuals that always cooperate cannot win the
competition against defectors in well-mixed populations. Here, we study the
evolution of a population where fitness is obtained in repeated public goods
games and players have a fixed probability of playing the next round. As a
result, the group size decreases during the game. The population is well-mixed
and there are only two available strategies: always cooperate (ALLC) or always
defect (ALLD). Through numerical calculation and analytical approximations we
show that cooperation can emerge if the players stay playing the game, but not
for too long. The essential mechanism is the interaction between the transition
from strong to weak altruism, as the group size decreases, and the existence of
an upper limit to the number of rounds representing limited time availability
Adoption of simultaneous different strategies against different opponents enhances cooperation
The emergence of cooperation has been widely studied in the context of game theory on structured populations. Usually the individuals adopt one strategy against all their neighbors. The structure can provide reproductive success for the cooperative strategy, at least for low values of defection tendency. Other mechanisms, such punishment, can also be responsible for cooperation emergence. But what happens if the players adopt simultaneously different strategies against each one of their opponents, not just a single one? Here we study this question in the prisoner dilemma scenario structured on a square lattice and on a ring. We show that if an update rule is defined in which the players replace the strategy that furnishes the smallest payoff, a punishment response mechanism against defectors without imputing cost to the punishers appears, cooperation dominates and, even if the tendency of defection is huge, cooperation still remains alive
On the synchronization of coupled random walks and applications to social systems
Some political strategies to win elections over the last years were based
heavily on fomenting general distrust in information institutions and favoring
distrustful sources. The misinformation pandemic has the straightforward
consequence that people do not believe any information unless it is compatible
with their own beliefs. We present a simple model to study the emergence of
consensus in opinion pools of uncertain agents that trust (couple to) their
neighbors (information sources) with strength K. We focus the studies on
regular lattices and linear coupling. Depending on the coupling constant, K,
and the propensity to choose an opinion (the probability to manifest a given
opinion in solitude), p_0, we get regions where consensus is surely reached
even in infinity systems (K greater than or equal to K_c), regions where
not-consensus is the only steady state (K lesser than K_c), and a region where
consensus on any opinion is transitory with each agent presenting periods of
strong oscillation of opinions before changing polarization (p_0 equal to p_c
and K greater than or equal K_c. The first model in this last region presents
transition probabilities identical to the voter model (p_0 equal to p_c and K
equal to K_c). Different upbringings, exposition to education biased to a
single political view, and previous coexistence with opinion polarized people
can change the opinion of agents in isolation. We model such characteristics
with heterogeneous populations (p^i_0 not equal to p^j_0 for some pairs of
nodes i,j). Such systems present regions where the coexistence of local
consensus (bulk-stable clusters of like-minded opinions), weak consensus
(bulk-unstable temporary clusters where contrary opinions emerge inside the
cluster), and distrust (random orientations that do not form clusters) are
possible.Comment: 14 pages, 7 figures, 4 section appendi
Distinguishing the opponents in the prisoner dilemma in well-mixed populations
Here we study the effects of adopting different strategies against different
opponent instead of adopting the same strategy against all of them in the
prisoner dilemma structured in well-mixed populations. We consider an
evolutionary process in which strategies that provide reproductive success are
imitated and players replace one of their worst interactions by the new one. We
set individuals in a well-mixed population so that network reciprocity effect
is excluded and we analyze both synchronous and asynchronous updates. As a
consequence of the replacement rule, we show that mutual cooperation is never
destroyed and the initial fraction of mutual cooperation is a lower bound for
the level of cooperation. We show by simulation and mean-field analysis that
for synchronous update cooperation dominates while for asynchronous update only
cooperations associated to the initial mutual cooperations are maintained. As a
side effect of the replacement rule, an "implicit punishment" mechanism comes
up in a way that exploitations are always neutralized providing evolutionary
stability for cooperation
Role-separating ordering in social dilemmas controlled by topological frustration
"Three is a crowd" is an old proverb that applies as much to social
interactions, as it does to frustrated configurations in statistical physics
models. Accordingly, social relations within a triangle deserve special
attention. With this motivation, we explore the impact of topological
frustration on the evolutionary dynamics of the snowdrift game on a triangular
lattice. This topology provides an irreconcilable frustration, which prevents
anti-coordination of competing strategies that would be needed for an optimal
outcome of the game. By using different strategy updating protocols, we observe
complex spatial patterns in dependence on payoff values that are reminiscent to
a honeycomb-like organization, which helps to minimize the negative consequence
of the topological frustration. We relate the emergence of these patterns to
the microscopic dynamics of the evolutionary process, both by means of
mean-field approximations and Monte Carlo simulations. For comparison, we also
consider the same evolutionary dynamics on the square lattice, where of course
the topological frustration is absent. However, with the deletion of diagonal
links of the triangular lattice, we can gradually bridge the gap to the square
lattice. Interestingly, in this case the level of cooperation in the system is
a direct indicator of the level of topological frustration, thus providing a
method to determine frustration levels in an arbitrary interaction network.Comment: 9 two-column pages, 9 figures; accepted for publication in Physical
Review