Australian Gouldian finches and the Hawk-Dove Theory
Article: http://news.discovery.com/animals/angry-birds-show-too-much-war-is-bad-140912.htm
A researcher’s theory that excessive conflict is bad for society has been demonstrated in an animal population, in findings motivated by game theory. As it turns out, aggressive and peaceful Gouldian finches can live together, as long as the aggressors are not too successful.
In this article, Professor Simon Griffith examined data of northern Australian Gouldian finches to see if it fitted the hawk-dove theory. The distinguishing characteristic of gouldian finches is that their coloration determines whether or not they are more likely to play a hawk strategy or play a dove strategy. The red-headed finch is aggressive and more likely to win a fight over a nest hollow, while the more numerous black-headed variety is more passive. The researchers were thus able to construct a model that predicted the number of hawks and doves as seen in real populations.
The hawk dove game is motivated by the story in which two animals are engaged in a contest to determine how a resource will be split between them. The animal can either behave aggressively (hawk strategy) or passively (dove strategy).
If a hawk fights a hawk, one of them will win the entire resource, getting benefit B. The loser will get injured and incur cost C. If we think of B and C as food calories, then the resource calories gained by the winner are positive, but the resource calories that the loser obtains is negative—the loser must devote calories to healing. Thus on average, a hawk will gain calories B/2 calories and lose C/2 calories in a hawk-hawk interaction, or a net change of (B-C)/2, in a hawk-hawk interaction.
In a hawk-dove interaction the dove does not fight but leaves. The hawk gets the full benefit B with no cost, and the dove gets a payoff of 0.
In a dove, dove interaction, doves split the resource evenly—each dove gets a payoff of B/2, without cost to anyone. The results can be summarized as follows:
|
Animal y |
|||
|
Animal x |
Hawk | Dove | |
| Hawk | (B-C)/2 , (B-C)/2 | B, 0 | |
| Dove | 0, B | B/2, B/2 | |
Assume a situation in which the field is completely doves; a single hawk will have it incredibly easy, obtaining a positive payoff B from any interaction.
Assume the opposite situation, a dove in an all hawk environment. If the cost C of a hawk-hawk interaction is greater than the benefit B, each hawk will experience an overall calorie loss as time goes on, whilst the Dove remains steady. Thus, the optimum mix of passive and aggressive behavior traits depends on the exact values of the costs and benefits.
Fights between red-headed finches incur high costs for the losers, thus it would be natural that there are less of them in the population compared to the black heads. Griffith and his team found that the hawk-dove game predicted that the optimal ratio of reds to blacks in the population would be 30:70 – which is exactly what is seen in the field.
Griffin says: “There is a trade off between how much time you spend fighting and how much time you spend at your nest looking after your chicks,” says Griffith. According to the hawk-dove theory, there is an optimal ratio of hawks to doves that allows for the fact that hawks who incur negative costs have decreased fitness, and are not as good as looking after their chicks.