Aggression
Aggression
Because members of a population have a common niche, there is a strong potential for conflict. Agonistic behavior is displayed when there is a contest that will determine which competitor gains access to a particular resource—for example, food or a mate. The encounter involves both threatening and submissive behavior, and may also involve tests of strength.More often, the contestants engage in threat displays that make them look large or fierce, usually through exaggerated posturing and vocalizations.Eventually one animal will stop threatening and end with a display of submission or appeasement, in effect calling an end to the fight.
Much agonistic behavior includes ritual activity so that serious harm
does not occur to either combatant. In many circumstances, escalated vio-lence over ownership of a mate or commodity is less an adaptive behavior than it is an exchange of signals, whether threatening or submissive. The agonistic signals provide information about the likely intentions and levels of commitment of the senders, as well as the relative fighting ability if escalation occurs. Any future interactions between the same two animals is usually settled much more quickly and in favor of the original victor.
Aggression can be used in a number of different interactions, such as those concerning territorial defense, potential mates, parent-offspring communication,social integration, and food. Conflict resolution usually occurs at short sender-receiver distances. The senders perform actions with tactical and signal functions, and the receivers make decisions based on all the information pooled from the cues and all secondary sources.
Intra– and Interspecific Competition
Conflicts usually arise between two more or less equal individuals who need the same resources to secure or increase their fitness. Both would like to obtain the resource with minimal fighting, so both want the other individual to back down. However, the two opponents are rarely of equal fighting ability or resource-holding potential. Each combatant wants to convey that it is the superior fighter and so uses displays of aggression. However, each one must also assess the other’s fighting ability relative to its own. Thus both individuals are senders and receivers simultaneously. The number of signals and tactical acts, and the truthfulness in the information being conveyed, must have something to do with the resolution of the conflict.
Types of Conflict
Intraspecific competition. When the conflict is intraspecific, between members of the same species, dominance hierarchies come into consideration. For example, placing several hens together that are unfamiliar with each other results in pecking and skirmishing. Eventually, a pecking order is established in which the most dominant hen, the alpha hen, controls the behavior of all the other hens, mostly through threat rather than actual pecking. The beta (second-ranked) hen does the same and so on to the lowest hen, the omega. The advantage of the top hens is that they are assured access to food resources. There is an advantage for the lowerranked hens as well, because the system ensures that they will not waste energy or risk injury in futile combat.
Interspecific competition. In the event that two or more species in a community rely on similar resources, they may be subject to interspecific competition. Actual fighting between members of two different species is termed interference competition, whereas the use or consumption of the “shared” resources is called exploitative competition. As population densities increase and resources such as food or nesting sites decrease, there is bound to be an increase in competition between the species. The same tactics of agonistic signaling apply here despite the variation in numbers and types of signals among the different species.
Strategies for Victory
Individuals in conflict can employ a number of strategies when assessing their opponent and the minimal level of aggression necessary to be the victor.
Hawk vs. Dove. One theory, termed “hawk versus dove,” helps explain why two animals do not always fight over the commodity that is sure to increase the fitness of the winner. Assuming the contestants are equal, there are two clear choices regarding the sought-after commodity: fight (as an aggressive hawk would do) or exhibit peaceable displays (as a dove would be more apt to do). When two hawks meet, they immediately fight over the commodity, with the loser suffering fight injuries as well as the cost of having lost the resource. Because the contest is assumed to be symmetric, each hawk wins half of its battles with other hawks. When a hawk meets a dove, the hawk becomes aggressive and the dove flees. Two doves will both use some costless exchangeof displays to decide who gets the commodity and who leaves peacefully.
The take game. Another contest that has been observed is a take game, which again involves two strategies: to be passive or to cheat. The passive animal minds its own business. The cheat, however, increases its own fitness at the expense of the fitness of others. The fishing activity of gulls and terns offers a good example. Some (passive) birds will concentrate solely on catching their own fish. Others (the cheats) will give up some of their own fishing time to monitor the success of other birds. When another bird catches a fish, the cheat will chase after the bird until the fish is dropped and then steal the fish. There is an advantage to cheating only if the bird can steal more fish than it would catch on its own.
The significance of this game is that once any cheats appear, the population will become most stable once all the organisms cheat. Evolution will have therefore lowered the average fitness of the population, a nonintuitive outcome given the assumption that evolution generally improves the average fitness of populations. It is only where evolution models a more passive approach to the acquisition of resources that populations enjoy improvements
in their average fitness. However, many evolutionary models lead to lower average fitness, and this simply reflects the costs of competition.
The war of attrition. Certain games employ strategies drawn from a continuous range of possibilities. A classic example is the war of attrition, in which two opponents compete by selecting an amount of strategic investment to be played during the particular confrontation. Neither opponent knows before the confrontation what level of investment the other has chosen. During the confrontation, the opponent that chose a larger investment wins. The investment might be the amount of time each is prepared to display to the other, or it might be how much energy the players put into the display.
It is unlikely that many animals meet the conditions for a symmetric
war of attrition, where all players suffer the same cost of display and would obtain the same benefit in winning. Usually the rate at which costs accumulate will not be the same for any two players. Also, the commodity over which they are fighting is likely to have different fitness values for each player. The critical issue thus becomes which player stands to gain the most from the commodity and lose the least while trying to win it. If the two animals knew at the outset which one was on superior footing, then there would be no confrontation and the animal that stood to lose the most would leave immediately.
However, such complete and accurate information is rarely available as two opponents face each other. The “game” that is then played is called an asymmetric war of attrition. A player that suspects it has the winner role will likely select a higher investment, while a player that suspects it has the inferior role will likely select a lower investment. Of course, it is possible that both players will decide they occupy the same role. These considerations emphasize the uncertainty inherent in this game. Depending on the presumptions of both animals, the confrontation may brief—or it may prove to be a long and vigorous fight. SEE ALSO Behavior; Behavioral Ecology; Dominance Hierarchy; Social Animals.
