How threat displays work: species-specific fighting techniques, weaponry and proximity risk

doi:10.1016/j.anbehav.2008.07.010

Animal Behaviour

Volume 76, Issue 5, November 2008, Pages 1455-1463

https://doi.org/10.1016/j.anbehav.2008.07.010 Get rights and content

Whether threat displays can reveal information about the strength or condition of the contestants is a long-debated issue. Enquist (1985, Animal Behaviour, 33, 1152–1161) showed that communication of such information is possible by means of choice of action in aggressive encounters. The key assumption of Enquist's model is that weak individuals signalling that they are strong (i.e. cheaters) cannot get away without fighting even if they want to, if they meet an honest strong individual. However, this assumption was not elaborated further and Enquist's model is often cited in support of Zahavi's handicap principle. Here I elaborate this assumption and show in terms of Enquist's model, by introducing spatial distance between opponents as a continuous variable, that it is the proximity of the opponent, what I call ‘proximity risk’, that maintains the honesty of threat displays. I show that the honest use of threat displays, sensu Enquist, is evolutionarily stable only within a certain distance threshold. Outside this threshold there may or may not be a zone where a mixture of honest and cheating displays can be evolutionarily stable. Outside this second zone threat displays are unreliable and thus expected not to be used and attended to. The model gives specific predictions about weaponry, species-specific fighting techniques and the value of these thresholds. Finally, I show that key predictions of the model, namely the relation between signal intensity, riskiness and proximity has strong support in the literature.

Section snippets

The model

Here I use Enquist's (1985) model, which can be seen as a modified version of the Hawk–Dove game (Maynard Smith 1982), where each player can be weak or strong and knows its own strength but not that of the opponent. The game has two steps. In the first step each player can choose between two cost-free signals A or B, then in the second round each animal can give up, attack unconditionally or attack if the opponent does not withdraw. Let V denote the value of the contested resource, and C_WW and C

Discussion

I have shown that it is the proximity risk that maintains the reliability of threat displays. There is a given threshold of distance (honest striking distance, x_HSD) within which honest signalling is an ESS; outside this threshold a mixed strategy supported by honest and cheating signallers is an ESS up to another threshold of distance (dishonest striking distance, x_DSD), while outside x_DSD threat displays are unreliable and thus will not be used. Depending on the value of the contested

Acknowledgments

I thank István Scheuring and József Garay for helpful comments. This work was supported by the European Union Framework 6 (Grant IST-FET 1940), the National Office for Research and Technology (Grant NAP2005/CKCHA005), and the Hungarian National Science Foundation (OTKA, Grant T049692).

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ArticlesHow threat displays work: species-specific fighting techniques, weaponry and proximity risk

Section snippets

The model

Discussion

Acknowledgments

Journal of Theoretical Biology

Animal Behaviour

Animal Behaviour

Animal Behaviour

Animal Behaviour

Journal of Theoretical Biology

Journal of Theoretical Biology

Animal Behaviour

Journal of Theoretical Biology

Journal of Theoretical Biology

Animal Behaviour

Journal of Theoretical Biology

Animal Behaviour

Journal of Theoretical Biology

Journal of Theoretical Biology

Articles
How threat displays work: species-specific fighting techniques, weaponry and proximity risk