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Possible mechanisms of establishing new customs in populations






 

All examples of specific behavioural traditions fixed in populations that have been described above are based on the spread of innovations. It means that behavioural patterns obtained by innovative animals through their individual experience are then assimilated by observers. However, the inclusion of members of animal communities in new behavioural traditions may be based on initial performances by few carriers of " at once and entirely" complex of actions. Let us consider from this standpoint the two examples which have been described in Chapter 23.

The first example concerns hunting for jumping springtails in Myrmica ants (Reznikova and Panteleeva, 2001, 2005). A strong correlation between dynamic density of victims in different plots and number of skilled hunters in ant families inhabiting these plots enabled us to suggest that encounters with lucky hunters promote awakening of predisposed hunting behaviour in those specimens which possess only a “sketch” of this complex hunting stereotype. It turned out that about 10% of family members display hunting for difficult-to-handle victims at early age, while within the rest of family members hunting behaviour is socially biased. In this part of the family, the more frequently ants observe collisions between victims and able hunters the more effectively their hunting patterns are shaped.

The second example concerns tool use in New Caledonian Crows. Social learning in combination with predisposition for manipulation with tools has been considered main mechanisms underlying tool manufacture in this species. Preparedness for tool using should be strong because New Caledonian Crows is a single bird species displaying total spread of similar tool use within populations (see Chapter 23 for details). Discovery of " at once and entirely" tool manufacture in a single chick in Kenward et al.’s (2005) study enables us to suggest a similar mechanism of spread of complex behavioural patterns within birds’ population to that of hunting in Myrmica ants. It is very likely that presence of individuals equipped with an inherited complete behavioural stereotype is necessary for triggering this stereotype in other members of population, and individual experience and maturation accomplish fixation of behavioural tradition in populations.

Such a strategy should be evolutionary stable in populations. We can call this strategy triggering dormant behavioural patterns. From the point of view of the present discussion this possible mechanism of fixation of behavioural patterns is of interest because its widespread in populations can be attributed to social facilitation, where carriers of whole patterns to be spread serve as catalysts of social learning.

Let us return to the grooming hand-clasp referred in the previous paragraph as a social custom which has been described as a newly implanted one for several communities of wild and captive chimpanzees (McGrew and Tutin, 1978; DeWaal, 1989; deWaal and Seres, 1997). It may be that the process of infection of chimpanzee communities by the new social custom which is based on highly stereotypic behavioural sequence such as grooming hand-clasp has much in common with the two examples just described. One can suggest that if there is a carrier of a specific behavioural pattern within a social group, then performance of such a pattern can trigger dormant behavioural patterns in some members of the group by means of relatively simple forms of social learning.

Another example that could be revisited from the standpoint of the hypothesis of triggering dormant behavioural patterns is preparedness for development of fear of “fear-relevant” (FR) objects in some species including humans. In Chapter 22 experiments of Mineka and co-authors with rhesus monkeys were described in details. At the first stage of those experiments the evidence has been obtained that lab-reared monkeys are not equipped by innate recognition of snakes. Nevertheless, the lab-reared monkeys can readily acquire a fear of snakes by observing wild conspecifics expressing fear of snakes. It may be conjectured that, when testing a sufficirntly large group of naï ve monkeys in the lab, experimenters would find a few carriers of the whole fear-pattern, that is, individuals equipped by innate recognition of snakes. Perhaps those few carriers of phobias of snakes and spiders within populations of our species mentioned in Chapter 22 reflect evolutionary stable strategy in hominids.

One of the most important factors that influences the effectiveness of transmission of new behavioural patterns within a community is the frequency of performance of this pattern which may be affected both by the frequency of displays by a single individual, and the number of skilled (or being equipped from birth) demonstrators.

Triggering of dormant behavioural patterns can be based on a cumulative effect. There are several field observations and experiments which support this hypothesis. Beck and Galef (1989) found that multiple demonstrators allowed naï ve rats to learn more quickly about the proper diet. In experiments with pigeons Lefebvre and Giraldeau (1994) demonstrated that the rate of adoption of innovations increases with the number of knowledgeable “tutors” and the number of uninformed observers. Experimenters presented pigeons, Columba livia, with the problem of pecking open a stoppered inverted test tube to obtain seeds. In the first series of experiments they presented observers by one, three, six, or nine demonstrators. In the second series of experiments they added two, five and eight naï ve observers to an initial group of observers. The observers learnt more slowly with increasing number of naï ve birds. At the same time, they learned more quickly with increasing “tutors” number. The rate of learning increased exponentially as a result of a dual effect of increased “tutors” number and reduced the number of naï ve birds which became informed and switched to “tutoring”. It is worth to note that the authors call informed pigeons tutors without quotes. It seems however that more simple forms of social learning than tutoring have been involved such as social facilitation and stimulus enhancement.

When analysing situations of transmission of new social customs and feeding techniques within populations an interesting question arises about which features animals have to possess in order to be innovators, which is considered in the next section.

 


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