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Alarm Calls

• Traditionally alarm calls were thought to be a means of kin selection or reciprocal altruism.   This means that when a creature issues an alarm call his motive is to warn his relatives of a predator's presence.  In such a model calling is assumed to be more of a communication with the creature's kin rather than the predator.
• While the prey may suffer a direct individual cost for calling, also reaps inclusive fitness benefits by warning his relatives of danger.  This benefits the species as a whole if each other's motives are wholly altruistic.
• Prey can directly benefit in fitness if altruistic behavior is mutual between all members.  Such actions while costly to the individual greatly increase the survivability of his relatives.

Alternative function of Alarm Calls

• However if we assume the above model then we also cannot deny that in some cases a creature employ's an alarm call much louder (and therefore more costly) than is necessary to simply warn his kin. This raises the possibility that alarm calls may be directed at the predator as some sort of communication.
• Alarm calling communicates a prey's "undesirability" to the predator.  Such a call may deter a predator from pursuing a prey that is aware of his presence.  For to do so would was time an energy better spent on an unsuspecting prey. Therefore the  prey avoids pursuit and predator doesn't expend time and energy on a prey that is potentially harder to catch
• This model is based on prey's observed risk of predation or how strongly it believes it's in danger.  The prey is not entirely certain of predator's presence.  Therefore his survival is dependent on how at risk he feels given the potential that a predator is there.  If the prey that are more certain of a predator's presence are also that the predators do not wish to peruse, signaling equilibrium (stable state) is possible.

Simplified Model

• Assumptions Made
• A predator will always be present in our model with the variable being whether or not it gives chase.  It's giving chase will be decided by one of two percent values.  The first value being used if it hears a call made by the prey, the second value being used if no call is heard.
• The prey will not prepare battlements unless it believes a predator is present.  Battlements are a convention used to represent some undesirable actions performed by the prey which will cost the prey some amount of energy, but will also cost the predator if it chooses to attack the prey.  The predator will both be affected directly, by paying some value when attacking the prey, and indirectly by only getting a percentage of the value it would have received from the prey.
• Taken from "Alarm calls as a costly signals of antipredator vigilance: the watchful babbler game" is the simplification of interaction.  Assuming at any one time that only one predator and one prey will interact.  Further simplifying the model, every time a prey and predator interact, they will be aware of one another's presence.

Honesty in calling

• Since certainty is never a constant in this model it can only be said that prey issue the alarm call either as a bluff or because they truly perceive a danger.
• The elevated cost of calling is shown by preparing battlements.
• At times a prey may only call, call and prepare battlements, prepare battlements and not call at all.
• The prey's sense of predation risk must accurately reflect the chance that a predator is present. Therefore prey that sense they're more likely to be caught have a higher chance of surviving.

 

A. Chase & A. Tran, 2001

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