4,907 research outputs found
Evolutionary Stability of Ecological Hierarchy
A self-similar hierarchical solution that is both dynamically and
evolutionarily stable is found to the multi dimensional Lotka-Volterra equation
with a single chain of prey-predator relations. This gives a simple and natural
explanation to the key features of hierarchical ecosystems, such as its
ubiquity, pyramidal population distribution, and higher aggressiveness among
higher trophic levels. pacs{87.23.Kg, 89.75.Da, 05.45.-a}
keywords{Lotka-Volterra equation, Trophic pyramid, Self-similarity}Comment: 4 Pages RevTeX4, 1 Fig, 1 Table, shortened by publishers reques
Mobility, fitness collection, and the breakdown of cooperation
The spatial arrangement of individuals is thought to overcome the dilemma of cooperation: When cooperators engage in clusters, they might share the benefit of cooperation while being more protected against noncooperating individuals, who benefit from cooperation but save the cost of cooperation. This is paradigmatically shown by the spatial prisoner's dilemma model. Here, we study this model in one and two spatial dimensions, but explicitly take into account that in biological setups, fitness collection and selection are separated processes occurring mostly on vastly different time scales. This separation is particularly important to understand the impact of mobility on the evolution of cooperation. We find that even small diffusive mobility strongly restricts cooperation since it enables noncooperative individuals to invade cooperative clusters. Thus, in most biological scenarios, where the mobility of competing individuals is an irrefutable fact, the spatial prisoner's dilemma alone cannot explain stable cooperation, but additional mechanisms are necessary for spatial structure to promote the evolution of cooperation. The breakdown of cooperation is analyzed in detail. We confirm the existence of a phase transition, here controlled by mobility and costs, which distinguishes between purely cooperative and noncooperative absorbing states. While in one dimension the model is in the class of the voter model, it belongs to the directed percolation universality class in two dimensions. DOI: 10.1103/PhysRevE.87.04271
Prisoner's Dilemma cellular automata revisited: evolution of cooperation under environmental pressure
We propose an extension of the evolutionary Prisoner's Dilemma cellular
automata, introduced by Nowak and May \cite{nm92}, in which the pressure of the
environment is taken into account. This is implemented by requiring that
individuals need to collect a minimum score , representing
indispensable resources (nutrients, energy, money, etc.) to prosper in this
environment. So the agents, instead of evolving just by adopting the behaviour
of the most successful neighbour (who got ), also take into account if
is above or below the threshold . If an
individual has a probability of adopting the opposite behaviour from the one
used by its most successful neighbour. This modification allows the evolution
of cooperation for payoffs for which defection was the rule (as it happens, for
example, when the sucker's payoff is much worse than the punishment for mutual
defection). We also analyse a more sophisticated version of this model in which
the selective rule is supplemented with a "win-stay, lose-shift" criterion. The
cluster structure is analyzed and, for this more complex version we found
power-law scaling for a restricted region in the parameter space.Comment: 15 pages, 8 figures; added figures and revised tex
Evolutionary prisoner's dilemma game on hierarchical lattices
An evolutionary prisoner's dilemma (PD) game is studied with players located
on a hierarchical structure of layered square lattices. The players can follow
two strategies [D (defector) and C (cooperator)] and their income comes from PD
games with the ``neighbors.'' The adoption of one of the neighboring strategies
is allowed with a probability dependent on the payoff difference. Monte Carlo
simulations are performed to study how the measure of cooperation is affected
by the number of hierarchical levels (Q) and by the temptation to defect.
According to the simulations the highest frequency of cooperation can be
observed at the top level if the number of hierarchical levels is low (Q<4).
For larger Q, however, the highest frequency of cooperators occurs in the
middle layers. The four-level hierarchical structure provides the highest
average (total) income for the whole community.Comment: appendix adde
Altruistic Contents of Quantum Prisoner's Dilemma
We examine the classical contents of quantum games. It is shown that a
quantum strategy can be interpreted as a classical strategies with effective
density-dependent game matrices composed of transposed matrix elements. In
particular, successful quantum strategies in dilemma games are interpreted in
terms of a symmetrized game matrix that corresponds to an altruistic game plan.Comment: Revised according to publisher's request: 4 pgs, 2 fgs, ReVTeX4. For
more info, go to http://www.mech.kochi-tech.ac.jp/cheon
Strategies for the evolution of sex
We find that the hypothesis made by Jan, Stauffer and Moseley [Theory in
Biosc., 119, 166 (2000)] for the evolution of sex, namely a strategy devised to
escape extinction due to too many deleterious mutations, is sufficient but not
necessary for the successful evolution of a steady state population of sexual
individuals within a finite population. Simply allowing for a finite
probability for conversion to sex in each generation also gives rise to a
stable sexual population, in the presence of an upper limit on the number of
deleterious mutations per individual. For large values of this probability, we
find a phase transition to an intermittent, multi-stable regime. On the other
hand, in the limit of extremely slow drive, another transition takes place to a
different steady state distribution, with fewer deleterious mutations within
the asexual population.Comment: RevTeX, 11 pages, multicolumn, including 12 figure
Robust ecological pattern formation induced by demographic noise
We demonstrate that demographic noise can induce persistent spatial pattern
formation and temporal oscillations in the Levin-Segel predator-prey model for
plankton-herbivore population dynamics. Although the model exhibits a Turing
instability in mean field theory, demographic noise greatly enlarges the region
of parameter space where pattern formation occurs. To distinguish between
patterns generated by fluctuations and those present at the mean field level in
real ecosystems, we calculate the power spectrum in the noise-driven case and
predict the presence of fat tails not present in the mean field case. These
results may account for the prevalence of large-scale ecological patterns,
beyond that expected from traditional non-stochastic approaches.Comment: Revised version. Supporting simulation at:
http://guava.physics.uiuc.edu/~tom/Netlogo
Aspiring to the fittest and promotion of cooperation in the prisoner's dilemma game
Strategy changes are an essential part of evolutionary games. Here we
introduce a simple rule that, depending on the value of a single parameter ,
influences the selection of players that are considered as potential sources of
the new strategy. For positive players with high payoffs will be considered
more likely, while for negative the opposite holds. Setting equal to
zero returns the frequently adopted random selection of the opponent. We find
that increasing the probability of adopting the strategy from the fittest
player within reach, i.e. setting positive, promotes the evolution of
cooperation. The robustness of this observation is tested against different
levels of uncertainty in the strategy adoption process and for different
interaction network. Since the evolution to widespread defection is tightly
associated with cooperators having a lower fitness than defectors, the fact
that positive values of facilitate cooperation is quite surprising. We show
that the results can be explained by means of a negative feedback effect that
increases the vulnerability of defectors although initially increasing their
survivability. Moreover, we demonstrate that the introduction of
effectively alters the interaction network and thus also the impact of
uncertainty by strategy adoptions on the evolution of cooperation.Comment: 7 two-column pages, 5 figures; accepted for publication in Physical
Review
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