176
P.L. Tyack and c.w. Clark
runaway process is the elaborate male display, but equally important is the
selection pressure for auditory mechanisms in females that allow them to
perceive and discriminate between subtle differences in the elaborate vocal
displays of males.
These three different models of sexual selection make different predictions about selection for specialized auditory processes. The male quality
model suggests females may need to select the male with the most extreme
development of a relatively simple acoustic feature, such as peak frequency
or formant dispersion. The sensory bias model suggests that sexual selection may take advantage of a preexisting bias, and may not create a selection pressure for changing this bias. The runaway process model suggests
the potential for an open-ended selection for increasingly more developed
displays and more refined preferences in females.
2.6.3 Threats and Fighting Assessment
Animals often find themselves in situations where they must compete with
a conspecific for access to a critical resource. In most of these contests,
it will be worth a competitor's while to gather some information on the
willingness and ability of its opponent to fight. Both competitors will often
have a shared interest in gaining this information, and many contests start
with a ritualized phase of exchanging displays. While such contests will
sometimes involve physical contact and injury, contests may be settled prior
to such escalation through a series of displays. If one contestant concludes
from this initial assessment phase that it would be likely to lose a fight, or
that the potential cost of injury outweighs the potential benefit of winning,
then it may gain by breaking off and leaving the contest (Krebs and Davies
1993). In this case, the contestant may benefit from producing a submissive
display to the opponent.
Two different models have dominated analysis of signals used in the early
stages of an aggressive contest. One model emphasizes how receivers may
attend to features of signals that are reliable indicators of fighting ability.
Typical attributes associated with fighting ability such as age, physical condition, or size cannot be changed without considerable cost. If a contestant
is using a signal to estimate the fighting ability of an opponent, then it is
critical for the signal to involve features that cannot be faked to increase
the apparent ability of the signaler. If an animal can use a signal to bluff
about its motivation or ability, then it will pay the opponent to call the bluff.
In many situations, it may even pay for the opponent to ignore this kind of
signal. This kind of logic has led biologists to emphasize the importance of
signals that cannot be faked because they are inherently linked to an
attribute associated with fighting ability.
Body size is often a good predictor of the outcome of fights in many
animal species (Krebs and Davies 1993). As was discussed in the context of
female choice, a variety of animal species assess the lowest frequency of
P.L. Tyack and c.w. Clark
runaway process is the elaborate male display, but equally important is the
selection pressure for auditory mechanisms in females that allow them to
perceive and discriminate between subtle differences in the elaborate vocal
displays of males.
These three different models of sexual selection make different predictions about selection for specialized auditory processes. The male quality
model suggests females may need to select the male with the most extreme
development of a relatively simple acoustic feature, such as peak frequency
or formant dispersion. The sensory bias model suggests that sexual selection may take advantage of a preexisting bias, and may not create a selection pressure for changing this bias. The runaway process model suggests
the potential for an open-ended selection for increasingly more developed
displays and more refined preferences in females.
2.6.3 Threats and Fighting Assessment
Animals often find themselves in situations where they must compete with
a conspecific for access to a critical resource. In most of these contests,
it will be worth a competitor's while to gather some information on the
willingness and ability of its opponent to fight. Both competitors will often
have a shared interest in gaining this information, and many contests start
with a ritualized phase of exchanging displays. While such contests will
sometimes involve physical contact and injury, contests may be settled prior
to such escalation through a series of displays. If one contestant concludes
from this initial assessment phase that it would be likely to lose a fight, or
that the potential cost of injury outweighs the potential benefit of winning,
then it may gain by breaking off and leaving the contest (Krebs and Davies
1993). In this case, the contestant may benefit from producing a submissive
display to the opponent.
Two different models have dominated analysis of signals used in the early
stages of an aggressive contest. One model emphasizes how receivers may
attend to features of signals that are reliable indicators of fighting ability.
Typical attributes associated with fighting ability such as age, physical condition, or size cannot be changed without considerable cost. If a contestant
is using a signal to estimate the fighting ability of an opponent, then it is
critical for the signal to involve features that cannot be faked to increase
the apparent ability of the signaler. If an animal can use a signal to bluff
about its motivation or ability, then it will pay the opponent to call the bluff.
In many situations, it may even pay for the opponent to ignore this kind of
signal. This kind of logic has led biologists to emphasize the importance of
signals that cannot be faked because they are inherently linked to an
attribute associated with fighting ability.
Body size is often a good predictor of the outcome of fights in many
animal species (Krebs and Davies 1993). As was discussed in the context of
female choice, a variety of animal species assess the lowest frequency of