Dear Enemies and the Prisoner's Dilemma: Why Should Territorial Neighbors Form Defensive Coalitions?

Abstract

SYNOPSIS. Game-theoretic arguments are used to derive two new hypotheses to explain why territorial residents so consistently defeat potential usurpers. Both hypotheses are based on help from established, familiar neighbors. The first hypothesis follows simply from Krebs' (1982) assertion that the value of a territory to a usurper must be decremented by the costs of negotiating dear-enemy relationships with the remaining neighbors. An implication is that the remaining neighbors will also have to pay these renegotiation costs if the usurper succeeds. The first hypothesis is that it may benefit a territorial animal to help its established neighbors defend so it can avoid having to renegotiate territorial boundaries with a new, unfamiliar neighbor. This hypothesis assumes net positive benefits to helping without requiring reciprocation. The second hypothesis requires reciprocation to compensate for immediate net costs of helping. An animal should help its neighbors fight off usurpers only if the neighbors will reciprocate. This hypothesis is based on the prisoner's dilemma game and builds on Axelrod's (1984) work. Cooperative defense (reciprocal help) can be an evolutionarily stable strategy (ESS) if several conditions are met. One critical condition is that the relationship between neighbors is relatively stable. Cooperative defense should help established neighbors retain their territories, and should therefore be a cause, as well as a consequence of stability. It is suggested that the necessary conditions are not very restrictive, that they are often met in nature, and that shared defense is observed but not recognized as such.

The social interaction role of song in song sparrows: implications for signal design

“…If territorial birds in nature use conventional matches (and to be clear: conventional matching has not yet been observed in the wild), then the process of negotiating with each neighbor long enough to establish conventional match pairings represents a potentially significant social investment. The benefits of conventional matching and the time investment it may take to develop the signals may be one of the factors behind the widely documented 'Dear Enemy' phenomenon in which neighbors show lower aggression towards each other than towards strangers (Fisher, 1954;Getty, 1987;Temeles, 1994).…”

Friendship, cliquishness, and the emergence of cooperation

“…We have avoided non-evolutionary pairwise tournaments and included mutation on all of our strategy parameters in order to avoid the restricted ecologies that have clouded prior work. Finally, the model permits us to examine prior assumptions about relationship decay in the IPD environment and to show the assumption of geometric decay is only valid in the long-run and not during initial interactions (Feldman and Thomas, 1987;Getty, 1987).…”

Tit for Tat in the Dear Enemy Relationship Between Territorial Females of a Cichlid Fish

“…The dear enemy effect is beneficial for participant territory owners because it allows them to reduce territorial defense costs and to spend their energies on other activities that may increase their fitness (e.g., Temeles, 1994;Leiser and Itzkowitz, 1999;Leiser, 2003;Carazo et al, 2007;Briefer et al, 2008). Explanations for the evolution of this relationship have invoked reciprocal altruism based on the tit for tat (TFT) strategy in an iterated Prisoner's Dilemma (Trivers, 1971(Trivers, , 1985Axelrod and Hamilton, 1981;Getty, 1987), and we do not know alternative mechanical hypotheses for this phenomenon.…”