FEATURE ARTICLE
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
Mike Mesterton-Gibbons, Eldridge Adams
The Value of Game Theory
It is not unusual for an exercise in game theory to remain partially inconclusive. On the one hand, game-theoretic models are valuable because they suggest ways to test new ideas. The damselfly model suggests a test—whether the reserves of the loser correlate positively with contest duration—for an evolutionary stable strategy in which the contestants cannot assess their opponents' strength. The stomatopod model suggests a test—whether animals that threaten and lose pay higher costs than those that lose without threatening—for the idea of an evolutionary stable strategy with partial bluffing. Finally, the spider model suggests a test—whether an intruder is almost as likely as an owner to win an actual fight—for the idea of an anti-Bourgeois evolutionary stable strategy. On the other hand, suggesting a test is not the same thing as conducting it, and the difficulties of doing so should not be underestimated. For example, the only way to measure resource-holding potential is to precipitate actual fights, which may be far from easy in a species as reclusive as the spider O. civitas.
In fact, the difficulties of testing the predictions of evolutionary game theory have led some to question its value. But games are not valuable solely because they suggest ways to test new ideas. They are also valuable because they allow us to explore the logic of a verbal argument rigorously, assuming biologically realistic ecotypes, and to determine when it is true and when it is false. As these cases illustrate, game theory often demonstrates what is difficult to intuit. As a result of exploring damselfly duels, we now understand that victory by stronger animals need not imply that strength is being assessed. As a result of investigating stomatopod strife, we now understand how bluffing can persist at a high frequency. And through analyzing spider spats, we now understand how a non-fighting population of usurpers can evolve, under decreasing predation, from a fighting population that ignores the asymmetry of ownership.
Perhaps non-assessment of strength, high-frequency bluffing and sequential displacement are all remarkably rare in nature. For example, the domino effect has not been observed in colonial spiders other than O. civitas. But it is rarely the commonplace that piques our interest. Rather, it is strange behavior that engages our attention and spurs us on to deeper understanding, even of the commonplace. In that regard, evolutionary games have proved their usefulness over and over again. They have become indispensable analytical tools toward progress in behavioral ecology.
» Post Comment