Neighbor intervention: a game-theoretic model.

Area of Science:

• Behavioral Ecology
• Evolutionary Game Theory
• Animal Behavior

Background:

• Territorial defense is crucial for resource acquisition and reproductive success.
• The potential benefit of neighbor intervention against intruders is to avoid costly renegotiation of territory boundaries.
• Previous theories suggested cooperation in territorial defense might require reciprocity.

Purpose of the Study:

• To quantify the conditions under which helping a neighbor defend territory is an evolutionarily stable strategy (ESS).
• To explore the role of fighting costs, renegotiation costs, and variation in fighting strength in cooperative territorial defense.
• To identify factors influencing the likelihood of neighbor intervention.

Main Methods:

• Development of a parameterized game-theoretic model involving residents, challengers, and potential allies.
• Analysis of simplified discrete games with zero variation in fighting strength.
• Inclusion of finite variation in fighting strength to explore interventional ESS.

Main Results:

• Neighbor intervention is an ESS only if fighting costs are low relative to renegotiation costs, or if fighting costs are high and fighting strength varies.
• Intervention occurs when the resident is unlikely to win alone, with factors like low home advantage, synergistic strengths, and low ally usurpation probability increasing intervention likelihood.
• The model explains observations in Australian fiddler crabs, including ally size relative to resident and intruder.

Conclusions:

• Cooperative territorial defense can evolve without reciprocity, driven by the strategic benefits of avoiding boundary renegotiation.
• The evolutionarily stable strategy for intervention depends critically on the relative costs of fighting versus renegotiation and the variation in combatant strength.
• Neighbor intervention is a conditional strategy influenced by ecological and social factors, not an inevitable outcome in territorial species.