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Ecological aspects of social learning






 

Opportunity for the exchange of information among individuals is one of important benefits of living in groups. Species differ in their abilities to use socially acquired information and, in particular, in their abilities to learn through traditions (see Fig. VIII-1). Members of social groups often monitor the behaviour of their companions in an attempt to gain information about the location of foraging sites or approaching predators. Using social cues provided inadvertently by individuals engaged in efficient performance (“inadvertent social information”, or ISI), animals rely on “public information” (PI) about the quality of the resource (Valone, 1989: Giraldeau et al., 2002; Danchin et al., 2004). In many cases, for group living animals the only socially acquired information available to individuals is the behavioural actions of others that expose their decisions, rather than initial stimuli on which these decisions are based. So an individual has to make a choice between possibilities to use socially generated cues or to rely on a personal decision basing on the stimuli that gained directly from its environment. A readiness to pay attention only to socially generated cues can reflect a level of conformity of an individual or of a whole group.

As it has been already noted more than once, social learning rarely, if ever, appear as a single source of knowledge during normal ontogenesis; instead, social learning combines with consequences of maturation and with of individual experience. The question of how readily animals learn - in particular, by means of social cues - about predators, food, suitable partners and other vital things is important not only from theoretical but also from applied perspective. Reintroduced and translocated individuals as well as those reared in captivity, are vulnerable to predation and starvation risks. It is practically important to estimate the contribution of each component into an integral picture of behaviour of a certain species, that is, the role of individual experience, inherited patterns and readiness for social learning. There are many experimental data demonstrating the role of social learning in concrete situations of foraging, mate choice and antipredator behaviour of different species.

A role of social learning in foraging. The idea that animals may observe others to get information about resource quality arose mostly in foraging context (for a review see: Danchin et al., 2004). Animals can use socially gained cues in the context of searching patchy distributed food or making decision about food availability and appropriateness.

One of the central problems of behavioural ecology is whether individual group members can improve estimation of quality of a food patch by combining their prior knowledge of the distribution of prey with the obtained public information. For example, European starlings (Sturnus vulgaris) and red crossbills (Loxia curvirostra) use a patch-foraging scenario (Charnov, 1976) and exploit prey hidden in soil (starlings) or within a tree crone (cross bills). These birds must probe repeatedly to estimate the current quality of a foraging patch. Both species observe their flockmates’s probing success and use this as PI to decide when to leave a patch in search of another (Templeton and Giraldeau, 1995). Public information can also be obtained heterospecifically. For instance, nine-spined sticklebacks (Pungitius pungitius) use the feeding behaviour of three-spined sticklebacks (Gasterosteus aculeatus) to select the most profitable patch to exploit (Coolen et al., 2003). In ants’ species communities dominating species use behavioural cues from more agile subdominants to obtain hidden food items (Reznikova, 1982, 2003; see details further in this Chapter).

Social facilitation of eating novel food has been found in many species. Nevertheless, there is a debate and equivocal evidence about the role of this source of knowledge in formation of foraging habits in animals. It is likely that different ontogenetic scenarios imply different roles of social learning in a wide variety of species. For example, in mammals preference for a particular food is shaped under influences of inherited predisposition, information gathered from smell of mother’s milk and faeces and supplemented with smell and taste of food items (Galef, 1993; Altbä cker et al., 1995). Infants manage to get novel food directly from mother’s mouth or by pushing her away from the food without ceremony. In some avian species young also learn to choose appropriate food from parents and then from conspecifics whereas in others individual learning based on inherited predisposition dominates (Lefebvre and Palameta, 1988).

Animals living in groups monitor each other every moment of their periods of activity and react on specific motions which send messages that food is available. For example, Brown and Laland (2002) have shown that the specific darting motion serves a cue to naive fish to learn to forage on novel prey items. They found that 100% of the individuals that paired with pre-trained fishes learned to accept the novel prey. Naive fishes paired with equally naive individuals actually performed worse (50%) than the individuals learning in isolation (73%).

Although social learning would be particularly advantageous when food can be poisonous, and some concrete data support this hypothesis (Mason and Reidinger, 1981; Fryday and Greig-Smith, 1994) some species do not rely on social information. For example, Japanese macaques and tufted capuchins rely on their own experience and not on what they see other group members doing in response to a decrease of food palatability (Visalberghi and Addessi, 2001). However, it is easier for many species to acquire food preference socially than to learn by themselves to avoid food that is poisonous. In Galef et al.’s (1985) experiments with rats some of the critical features of the social interactions preceding formation of food preference have been revealed. The experimenters used a simple apparatus to allow one rat to smell food on an anaesthetised demonstrator rat (that one can call a “sleeping rat beauty”). An observer rat was placed into the basket of the apparatus, and an anaesthetised (and thus unintentional) demonstrator was placed into a wire mesh basket (Fig. VIII-2). Some demonstrators had food dusted on their faces, and others had food placed directly into their stomachs through a tube. In both cases the observers subsequently showed a preference for the flavoured diet that had just been fed to the demonstrator. However, if the rear end of the demonstrator was dusted with food and placed foremost in the basket, then only a slight preference for the food was demonstrated. Finally, if a wad of cotton wool, rather than a rat, was placed in the basket, then despite being dusted with food, there was no change in the attractiveness of the food. Thus the demonstrator does not need to be active to encourage the development of a food preference in another rat. But the demonstrator should be a rat, and the observer must be sure that the demonstrator touched the food by its face, not by a tail!

In experiments with domestic chickens Turner (1965) revealed that young chicks respond strongly to a pecking model of a hen.

Sherwin et al. (2002) demonstrated that avian social learning should be not fundamentally different that of mammals, and the similar features of the social interactions influence food preference in these groups of animals. In particular, it turned out that the more enthusiastically a demonstrator pecks novel food items, the more items observers consume. It is interesting to note that even in such socially independent chicks as brush-turkeys (see Chapters 22 and 24 for details) young chicks react positively to a pecking conspecific. This has been demonstrated by Gö th and Evans (2004) in experiments with the use of naive chicks and realistic pecking robots (Fig. VIII-3). Megapode chicks do not form bonds with their parents. They hatch with a general tendency to respond to some common features of food objects, such as contrast, movement and reflective surfaces, and while trial and error is initially important, they successfully aim their pecks at edible items soon after hatching.

Besides, megapode chicks show the predisposition in response to conspecific chicks of similar age. A pecking conspecific indicating food might speed up the transition from trial and error searching to more selective pecking through social facilitation.

Mate choice copying. It is an intriguing question to what extent social factors can influence the choice of sexual partner. Female mating decisions are often influenced by exposure to the mating interaction of others. This style of mating behaviour is called “mate choice copying” which is said to occur when the probability of an individual selecting another as a sexual partner increases because other individuals (of the same sex) have selected the same partner (Gibson and Hoglund, 1992). Mate choice copying has been reported in several species of birds and fishes. To estimate the role of social information in mate choice, it is necessary to separate the signals deliberately produced by displaying males from the cues that are inadvertently produced by females that make their choices.

Dugatkin (1992) has elaborated an experimental paradigm to investigate this problem. In his study on guppies two males were secured at the ends of an aquarium, one with a demonstrator female nearby. The observer, another female, placed centrally, watched the other female interact with one of the males. When, after the demonstrator has been removed, the observer was allowed to choose between the two males, she consistently chose the male that the first female chose. Multiple comparisons with choices that were made by control females enabled researchers to suggest that females follow a rule: “if this male is good for another female, he is good for me”, that is, they utilise the presence of the female near a male as an indication of his quality. At the same time, females take into account key features of males themselves. For guppy tail coloration is significant: in the case when males differ slightly by this sign, a female chooses more “popular” male, but if the male has a pale-coloured tail, he has no chance to be selected by a female (Dugatkin and Godin, 1992). There are, however, many other mating patterns in fishes that do not include “mate choice copying” (for a review see: Brown and Laland, 2003).

Galef and White (1998, 2000) have suggested an interesting experimental technique in order to explore social influences on reproductive behaviour. They used Japanese quail (Coturnix japonica) as a model species. Researchers changed typical look of birds by adding them a novel trait, namely, a white hat. Females that observed that males with novel traits mated successfully preferred males that possess similar white hats. Applying the same methodical trick, Swaddle et al. (2005) have revealed mate choice copying in zebra finch. Females preferred males that were wearing the same leg band colour as the apparently “chosen” males, that is, being demonstrated as bonded paired with other females. These studies show that mate preference can spread rapidly through population by social mechanisms, affecting the strength of sexual selection even in a monogamous species.

Public information about danger. Acquiring information about danger such as predators by use of social cues can sufficiently decrease the level of lethal risk for group living animals. Utilising information gained from observing conspecifics is especially advantageous as it allows to adopt appropriate behaviours without the need to independently verify the approach of a predator (Brown and Laland, 2003; Caro, 2005).

The general tendency to copy flee-responses of an entire group (flock, herd, or shoal) is based on a simplest form of social learning, namely, on contagion. A panic reaction of a single individual can trigger similar reactions of other members of the group. Individuals react to the flight response of neighbours rather than directly to the advancing predator itself. Synchronous predator responses seem to be cooperative at least in some species. For example, in herrings’ schools, attacks from predatory fish and killer whales induce massive predator-response patterns at the school level, including bend, vacuole, hourglass, pseudopodium, herd, split, and “tight-ball” formation within the shoal (Axelsen et al., 2001). It is still a discussible question whether the repertoire of predator responses observed in large groups of fishes and birds can be interpreted as a range of co operative tactics to trick predators, or different individual tactics determine the outcome at group level (Couzin et al., 2005).

Many researchers reported social learning at a group level when, after observing predator responses of a neighbouring group, a school of fishes or a flock of birds react much more readily to the approach of a predator (for a review see Brown and Laland, 2003). For example, minnows showed a significant increase in the frequency of flight responses after observing the flight responses of minnows in a neighbouring tank that had been threatened by a predator (Magurram and Higham, 1988). Animals often use predator responses of other species as social cues to lean to avoid danger, and this may include formation of reaction to a novel predator. For example, Curio (1988) has shown that blackbirds learn to mob a species of bird to which they were initially indifferent (Australian honeyeater, Philemon corniculatus) once they have seen conspecific apparently mobbing it.

 


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