29,860 research outputs found
Consequences of fluctuating group size for the evolution of cooperation
Studies of cooperation have traditionally focused on discrete games such as
the well-known prisoner's dilemma, in which players choose between two pure
strategies: cooperation and defection. Increasingly, however, cooperation is
being studied in continuous games that feature a continuum of strategies
determining the level of cooperative investment. For the continuous snowdrift
game, it has been shown that a gradually evolving monomorphic population may
undergo evolutionary branching, resulting in the emergence of a defector
strategy that coexists with a cooperator strategy. This phenomenon has been
dubbed the 'tragedy of the commune'. Here we study the effects of fluctuating
group size on the tragedy of the commune and derive analytical conditions for
evolutionary branching. Our results show that the effects of fluctuating group
size on evolutionary dynamics critically depend on the structure of payoff
functions. For games with additively separable benefits and costs, fluctuations
in group size make evolutionary branching less likely, and sufficiently large
fluctuations in group size can always turn an evolutionary branching point into
a locally evolutionarily stable strategy. For games with multiplicatively
separable benefits and costs, fluctuations in group size can either prevent or
induce the tragedy of the commune. For games with general interactions between
benefits and costs, we derive a general classification scheme based on second
derivatives of the payoff function, to elucidate when fluctuations in group
size help or hinder cooperation.Comment: 22 pages, 5 figure
Social Network Reciprocity as a Phase Transition in Evolutionary Cooperation
In Evolutionary Dynamics the understanding of cooperative phenomena in
natural and social systems has been the subject of intense research during
decades. We focus attention here on the so-called "Lattice Reciprocity"
mechanisms that enhance evolutionary survival of the cooperative phenotype in
the Prisoner's Dilemma game when the population of darwinian replicators
interact through a fixed network of social contacts. Exact results on a "Dipole
Model" are presented, along with a mean-field analysis as well as results from
extensive numerical Monte Carlo simulations. The theoretical framework used is
that of standard Statistical Mechanics of macroscopic systems, but with no
energy considerations. We illustrate the power of this perspective on social
modeling, by consistently interpreting the onset of lattice reciprocity as a
thermodynamical phase transition that, moreover, cannot be captured by a purely
mean-field approach.Comment: 10 pages. APS styl
Eco-evolutionary dynamics of social dilemmas
Social dilemmas are an integral part of social interactions. Cooperative
actions, ranging from secreting extra-cellular products in microbial
populations to donating blood in humans, are costly to the actor and hence
create an incentive to shirk and avoid the costs. Nevertheless, cooperation is
ubiquitous in nature. Both costs and benefits often depend non-linearly on the
number and types of individuals involved -- as captured by idioms such as `too
many cooks spoil the broth' where additional contributions are discounted, or
`two heads are better than one' where cooperators synergistically enhance the
group benefit. Interaction group sizes may depend on the size of the population
and hence on ecological processes. This results in feedback mechanisms between
ecological and evolutionary processes, which jointly affect and determine the
evolutionary trajectory. Only recently combined eco-evolutionary processes
became experimentally tractable in microbial social dilemmas. Here we analyse
the evolutionary dynamics of non-linear social dilemmas in settings where the
population fluctuates in size and the environment changes over time. In
particular, cooperation is often supported and maintained at high densities
through ecological fluctuations. Moreover, we find that the combination of the
two processes routinely reveals highly complex dynamics, which suggests common
occurrence in nature.Comment: 26 pages, 11 figure
Synergy and Group Size in Microbial Cooperation
Microbes produce many molecules that are important for their growth and development, and the consumption of these secretions by nonproducers has recently become an important paradigm in microbial social evolution. Though the production of these public goods molecules has been studied intensely, little is known of how the benefits accrued and costs incurred depend on the quantity of public good molecules produced. We focus here on the relationship between the shape of the benefit curve and cellular density with a model assuming three types of benefit functions: diminishing, accelerating, and sigmoidal (accelerating then diminishing). We classify the latter two as being synergistic and argue that sigmoidal curves are common in microbial systems. Synergistic benefit curves interact with group sizes to give very different expected evolutionary dynamics. In particular, we show that whether or not and to what extent microbes evolve to produce public goods depends strongly on group size. We show that synergy can create an âevolutionary trapâ which can stymie the establishment and maintenance of cooperation. By allowing density dependent regulation of production (quorum sensing), we show how this trap may be avoided. We discuss the implications of our results for experimental design
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