Michael Mesterton-Gibbons

Cooperation Among Unrelated Individuals: Evolutionary Factors

There are three categories of cooperation among unrelated individuals: group-selected behavior, reciprocal altruism, and by-product mutualism. A simple two-strategy game, the cooperators dilemma, which generalizes the well-known prisoners dilemma, provides a coherent framework for distinguishing the mechanisms that support cooperation in each category. The mechanism for cooperation in group-selected behavior is deme structure; variance among trait groups allows natural selection to favor individuals in groups with a higher frequency of cooperators. A prerequisite for this mechanism to work is differential productivity of trait groups. The mechanism for cooperation in reciprocal altruism is scorekeeping, which allows cooperators to relatiate against noncooperators by conditioning their behavior on that of others. A prerequisite for this mechanism is that the expected number of interactions between individuals be sufficiently high. In nonsessile organisms, individuals must typically have a sufficiently well-developed neural apparatus to recognize opponents and remember their actions on previous encounters. The mechanism for cooperation in by-product mutualism is the common enemy of a sufficiently adverse environment. A prerequisite for this mechanism is the boomerang factor, that is, any uncertainty that increases the probability that a noncooperator will be the victim of its own cheating. These mechanisms may operate, alone or together, in widely divergent taxa. Empirical studies suggest that cooperation among unrelated confoundresses in the desert seed harvester ant, Messor pergandei, exemplifies group-selected behavior. Other recent experiments suggest that predator inspection in fish may satisfy the prerequisites for cooperation via reciprocity between nonsessile organism. Cooperative hunting of large prey in lions appears to be an example of by-product mutualism. Both theoretical and empirical work are needed to distinguish among these possibilities, and future research directions are discussed.

An introduction to game-theoretic modelling

Noncooperative games Evolutionary stability and other selection criteria Cooperative games in strategic form Characteristic function games Cooperation and the prisoners dilemma More population games Appraisal The tracing procedure Solutions to selected exercises Bibliography Index.

A technique for finding optimal two-species harvesting policies

Abstract This paper describes a technique to find the optimal harvesting policy for a Lotka-Volterra ecosystem of two interdependent populations when harvest rate is proportional to harvesting effort and either a single stock is selectively harvested or both stocks are harvested together. A problem that yields to this technique is Chaudhuris ( Ecol. Model. , 41: 17–25, 1986) previously unsolved problem of harvesting two competing species. The solution reveals that even if two species would coexist in the absence of harvesting, one species may be driven to extinction by the optimal policy if it is sufficiently more catchable than the other. It is suggested that the technique may be widely applicable in ecological modelling, and other recent applications are described.

Cooperation among unrelated individuals: reciprocal altruism, by-product mutualism and group selection in fishes

Cooperation among unrelated individuals can evolve not only via reciprocal altruism but also via trait-group selection or by-product mutualism (or some combination of all three categories). Therefore the (iterated) prisoners dilemma is an insufficient paradigm for studying the evolution of cooperation. We replace this game by the cooperators dilemma, which is more versatile because it enables all three categories of cooperative behavior to be examined within the framework of a single theory. Controlled studies of cooperation among fish provide examples of each category of cooperation. Specifically, we describe reciprocal altruism among simultaneous hermaphrodites that swap egg parcels, group-selected cooperation among fish that inspect dangerous predators and by-product mutualism in the cooperative foraging of coral-reef fish.

Models of coalition or alliance formation

More than half a century has now elapsed since coalition or alliance formation theory (CAFT) was first developed. During that time, researchers have amassed a vast amount of detailed and high-quality data on coalitions or alliances among primates and other animals. But models have not kept pace, and more relevant theory is needed. In particular, even though CAFT is primarily an exercise in polyadic game theory, game theorists have devoted relatively little attention to questions that motivate field research, and much remains largely unexplored. The state of the art is both a challenge and an opportunity. In this review we describe a variety of game-theoretic and related modelling approaches that have much untapped potential to address the questions that field biologists ask.

Animal Contests as Evolutionary Games

Animal Contests as Evolutionary Games: Paradoxical behavior can be understood in the context of evolutionary stable strategies. The trick is to discover which game the animal is playing Author(s): Michael Mesterton-Gibbons and Eldridge S. Adams Reviewed work(s): Source: American Scientist, Vol. 86, No. 4 (JULY-AUGUST 1998), pp. 334-341 Published by: Sigma Xi, The Scientific Research Society Stable URL: http://www.jstor.org/stable/27857057 . Accessed: 14/11/2011 21:23

Ecotypic variation in the asymmetric Hawk-Dove game: When is Bourgeois an evolutionarily stable strategy?

SummaryThis paper develops a mathematical model of an iterated, asymmetric Hawk-Dove game with the novel feature that not only are successive pairs of interactants — in the roles of owner and intruder contesting a site — drawn randomly from the population, but also the behaviour adopted at one interaction affects the role of a contestant in the next. Under the assumption that a site is essential for reproduction, the evolutionarily stable strategy (ESS) of the population is found to depend on the probability, w, that the game will continue for at least a further period (which is inversely related to predation risk), and five other parameters; two of them are measures of site scarcity, two are measures of fighting costs, and the last is a measure of resource holding potential (RHP). Among the four strategies — Hawk (H), Dove (D), Bourgeois (B) and anti-Bourgeois (X) — only D is incapable of being an ESS; and regions of parameter space are found in which the ESS can be only H, or only X, or only B; or either H or X; or either X or B; or either H or B; or any of the three. The scarcer the sites or the lower the costs of fighting, or the lower the value of w, the more likely it is that H is an ESS; the more abundant the sites or the higher the costs of fighting, or the higher the value of w, the more likely it is that X or B is an ESS. The different ESSs are interpreted as different ecotypes. The analysis suggests how a non-fighting population could evolve from a fighting population under decreasing risk of predation. If there were no RHP, or if RHP were low, then the ESS in the non-fighting population would be X; only if RHP were sufficiently high would the ESS be B, and the scarcer the sites, the higher the RHP would have to be. These conclusions support the thesis that if long-term territories are essential for reproduction and sites are scarce, then ownership is ruled out not only as an uncorrelated asymmetry for settling disputes in favour of owner, but also as a correlated asymmetry.

Variation between Self- and Mutual Assessment in Animal Contests

Limited resources lead animals into conflicts of interest, which are resolved when an individual withdraws from a direct contest. Current theory suggests that the decision to withdraw can be based on a threshold derived from an individual’s own state (self-assessment) or on a comparison between their own state and their opponent’s (mutual assessment). The observed variation between these assessment strategies in nature does not conform to theory. Thus, we require theoretical developments that explain the functional significance of different assessment strategies. We consider a hawk-dove game with two discrete classes that differ in fighting ability, in which the players strategically decide on their investment toward mutual assessment. Analysis of the model indicates that there are simultaneous trade-offs relating to assessment strategies. First, weak individuals in a population must decide on whether to acquire information about their opponents at the cost of providing opponents with information about themselves. Secondly, all individuals must decide between investing in mutual assessment and being persistent in contests. Our analysis suggests that the potential for individuals to make errors during contests and differences in the consequences of sharing information within a population may serve as fundamental concepts for explaining variation in assessment strategy.

On sperm competition games: incomplete fertilization risk and the equity paradox.

Evolutionary game theory has been used to predict the effect on sperm expenditure of a trade–off between the value of a mating and the cost of its acquisition. In particular, G. A. Parker has predicted that if two males ‘know’ whether they are first or second to mate, but these roles are assigned randomly, then sperm numbers should be the same for both males whether the ‘raffle’ for fertilization is fair or unfair. This prediction relies on the assumption that, in the absence of sperm competition, ejaculates would always contain enough sperm to ensure complete fertilization after mating. The slightest risk of incomplete fertilization, however, is enough to ensure that favoured males expend more than disfavoured males in the presence of sperm competition, unless the competition is perfectly fair. Divergence of expenditures increases with unfairness until unfairness reaches a critical value, beyond which a disfavoured male should no longer compete. The higher the fertilization risk, the lower the critical unfairness. All predictions are independent of the probability of mating first or second. Implications are discussed for the mechanisms that underlie sperm competition.

Landmarks in Territory Partitioning: A Strategically Stable Convention?

A convention is a rule based on arbitrary cues that allows quick resolution of potentially protracted disputes. A familiar example is the Bourgeois strategy, in which the second of two animals to discover a resource yields it to the first, even though it may be stronger than its opponent. Here we develop a game‐theoretic model to show that neighbors with imperfect information about one another’s fighting abilities can be favored to accept a landmark as the designator of a territory boundary, even when the resulting territory is smaller than the one that would have been won through fighting. Thus, the use of landmarks or other mutually obvious solutions can serve as a convention for territory partitioning. For a distribution of fighting ability with low variance and high skew, there is a remarkably high probability that an animal will accept a smaller territory than it would have won through fighting. The analysis provides a possible explanation for the observed use of landmarks as boundary markers by territorial animals in a variety of taxa, including birds, fish, insects, and mammals. The analysis also suggests why territory boundaries are stable, once established, despite changes in characteristics of the residents or the environment.