Biology Reference
In-Depth Information
which have been referred to by terms such as 'punishment' 'policing', and 'sanctions'
(Frank, 2003). The general point here is that is if there is a mechanism that rewards
cooperators and/or punishes free riders (cheats), then this can alter the benefit/cost
ratio of helping, and hence favour cooperation.
This can be illustrated by adding some form of enforcement to the Prisoner's
dilemma. For example, imagine that an individual who defected could be punished
by the other player. If the cost of this punishment outweighed the benefit of
exploitation, then this punishment mechanism would remove any benefit of free
riding, and hence make cooperation the best strategy, irrespective of what the other
player does.
We discussed reciprocity first, and in such detail, even though it is a relatively
unimportant enforcement mechanism, because it provides a good way of introducing
the basic issues, and has attracted the most attention. Now, we will use specific examples
to illustrate how some other enforcement mechanisms can work.
There are many
way in which
cooperation can
be enforced
Infanticide and eviction in meerkats
One way to enforce cooperation is to harass potential helpers and, hence, reduce their
ability to breed independently. Andy Young and colleagues investigated an example of
this in meerkats. It had been previously observed that about one month before a
dominant female gives birth she becomes aggressive towards some of the subordinates
in the group and drives them from the group until her litter is born. Young
et al
. (2006)
found that this aggression was not random - it was directed towards the subordinate
females in the group who were pregnant, or most likely to become pregnant (older and
less related to the dominant). This has a large negative impact on the likelihood that the
subordinates will reproduce and so produce offspring that will compete for resources
with the dominant's young. Whilst they are evicted, females spend their time alone or
with other evictees, leading to elevated levels of stress hormones, a higher probability
that a litter is aborted, a reduced rate of conception and a decrease in body weight
(Figs. 12.8a-12.8c). In addition, this removes the subordinate females when they may
be a danger to the offspring of the dominant female. In cases where pregnant
subordinates are not evicted, they have been observed to attack and kill, and then
usually eat, pups that were recently born to the dominant female (Young & Clutton-
Brock, 2006). This effect is substantial, with the probability that the dominant's young
survive being reduced by approximately 50% if one or more subordinate females are
pregnant when the litter is born (Fig. 12.8d).
Dominant
meerkats evict
subordinates to
prevent them
breeding
Punishment in birds and fish
Another way in which cooperation could be enforced is by punishing individuals that
do not cooperate. This increases the relative benefit of cooperation, because it leads to
a cost of not cooperating. In many cooperative breeding birds, young individuals
temporarily delay dispersal and independent reproduction, and instead remain in their
natal nest to help rear other offspring. Raoul Mulder and Naomi Langmore (1993)
tested whether punishment could play a role in explaining helping behaviour amongst
superb fairy-wrens. To test this, they removed helpers and held them in captivity for
