CHAPTER ONE--CONTENTS

Game Theory

Game theory allows biologists to model how evolution affects strategies and tactics. When thinking about an evolutionary game, the biologist precisely defines the participants, their goals, and the actions they can take to meet the goals. Generally, there are many different possible strategies but some are obviously faulty. An animal will never win a competition for food game, for example, if its strategy is to not eat.

The prisoner's dilemma is an example of a game for which researchers have defined several different strategies. The hawk versus dove game is a little less complex, as there are fewer possible strategies. Prediction games are complicated, but useful, in that they allow an animal to choose a strategy based on predictions about future environments.

Once the strategies are defined the next step is to play them against each other. A researcher or student can simply try this, exploring the success or failure of each strategy against each other strategy. If many trials are required to discover the most successful strategies, then its probably easier to program a computer to play the game against itself, and to have the computer track the results.

Games become more complicated if strategies contain conditional responses. In prisoner's dillema, for example, animal "A" might respond in one way if "B" has just defected, and another if "B" has just cooperated. The most complicated conditional strategies involve learning, so that an animal can change its behavior depending on the personality of its opponent.

An evolutionary stable strategy, or ESS, is a strategy which cannot be dislodged by the presence of another strategy in the population of animals. In some games there is only one ESS, and all successful animals play that ESS.

In other games more than one strategy can coexist. Conditions may fluctuate so that one ESS does well under some circumstances and the other ESS does well when conditions change. If the rate of evironmental fluctuation is faster than the rate of selection in removing the alernative strategies, more than one strategy persists. In some cases a strategy may persist at the same time as another because it does well when played against another ESS, but poorly when played against itself.

Davis, M. D. 1983. Game theory, a nontechnical introduction. Dover: Mineola, New York.

Dugatkin, L. A. and H. K. Reeve. 1998. Game theory and animal behavior. Oxford University Press: Oxford.