Social foraging: individual learning and cultural transmission of innovations

We present two stochastic models of individual and social learningthat count the number of individuals exhibiting a learned, resource-producingtrait in a group of social foragers. The novelty of our modelingresults from incorporating the empirically based assumptionthat rates of both individual and social learning should dependon the frequency of the learned trait within the group. Whenresources occur as clumps shared by group members, a naive individual'sacquisition of the skill required for clump discovery/productionshould involve opposing processes of frequency dependence. Theopportunity to learn via cultural transmission should increasewith the trait's frequency, but the opportunity for learningindividually should decrease as the trait's frequency increases.The results of the model suggest that the evolution of the capacityfor cultural transmission may be promoted in environments wherescrounging at resource clumps inhibits rates of individual learning.     

Influence of prey foraging posture on flight behavior and predation risk: predators take advantage of unwary prey

Foraging in animals is often associated with characteristicbody postures, such as the head-down posture. When foragingconflicts with the ability to detect predators or to flee, individualsmay incur a greater risk of mortality to predation than otherwise.Here we investigate the influence of different foraging postures(horizontal versus nose-down body posture) on the ability ofindividuals to respond to approaching predators and on the riskof mortality to predation in the guppy (Poecilia reticulata).Individuals engaged in nose-down foraging were assumed to beable to visually scan a smaller area for predators and to escapeless effectively due to their body posture, and thus are morevulnerable to stalking predators than horizontally foragingones. In a first experiment, we separately exposed nonforaging,horizontally foraging, and nose-down foraging guppies to anapproaching cichlid fish predator model. Nonforaging guppiesreacted sooner to and initiated flight further away from theapproaching model than did foraging fish collectively, and horizontallyforaging individuals responded sooner to the model than nose-downforaging ones. Comparing all test guppies, nose-down foragingindividuals were the most likely not to exhibit any responseto the predator model. When presented with a simultaneous choiceof two guppies behind a one-way mirror, individual blue acaracichlid (Aequidens pulcher), a natural predator of the guppy,preferred to attack foraging guppies over nonforaging ones andnose-down foraging guppies over horizontally foraging individuals.In a final experiment with free-swimming cichlids and guppies,we demonstrated that individual risk of predation for guppiesforaging nose down was greater than for guppies foraging horizontally,and both were at greater risk than nonforaging guppies. Thislatter result is consistent with the above differences in theguppy's responsiveness to approaching predators depending ontheir foraging behavior, and with the finding that cichlid predatorspreferred fish that were less likely to show any response tothem. Our results therefore indicate that the ability to respondto approaching predators and the risk of mortality to predationin the guppy is strongly influenced by their foraging activity,and in particular their foraging posture, and that cichlid predatorspreferentially select less wary and more vulnerable guppies.[BehavEcol 7: 264–271 (1996)]     

Beyond existence and aiming outside the laboratory: estimating frequency-dependent and pay-off-biased social learning strategies

The existence of social learning has been confirmed in diverse taxa, from apes to guppies. In order to advance our understanding of the consequences of social transmission and evolution of behaviour, however, we require statistical tools that can distinguish among diverse social learning strategies. In this paper, we advance two main ideas. First, social learning is diverse, in the sense that individuals can take advantage of different kinds of information and combine them in different ways. Examining learning strategies for different information conditions illuminates the more detailed design of social learning. We construct and analyse an evolutionary model of diverse social learning heuristics, in order to generate predictions and illustrate the impact of design differences on an organism's fitness. Second, in order to eventually escape the laboratory and apply social learning models to natural behaviour, we require statistical methods that do not depend upon tight experimental control. Therefore, we examine strategic social learning in an experimental setting in which the social information itself is endogenous to the experimental group, as it is in natural settings. We develop statistical models for distinguishing among different strategic uses of social information. The experimental data strongly suggest that most participants employ a hierarchical strategy that uses both average observed pay-offs of options as well as frequency information, the same model predicted by our evolutionary analysis to dominate a wide range of conditions.     

How copying affects the amount, evenness and persistence of cultural knowledge: insights from the social learning strategies tournament

Darwinian processes should favour those individuals that deploy the most effective strategies for acquiring information about their environment. We organized a computer-based tournament to investigate which learning strategies would perform well in a changing environment. The most successful strategies relied almost exclusively on social learning (here, learning a behaviour performed by another individual) rather than asocial learning, even when environments were changing rapidly; moreover, successful strategies focused learning effort on periods of environmental change. Here, we use data from tournament simulations to examine how these strategies might affect cultural evolution, as reflected in the amount of culture (i.e. number of cultural traits) in the population, the distribution of cultural traits across individuals, and their persistence through time. We found that high levels of social learning are associated with a larger amount of more persistent knowledge, but a smaller amount of less persistent expressed behaviour, as well as more uneven distributions of behaviour, as individuals concentrated on exploiting a smaller subset of behaviour patterns. Increased rates of environmental change generated increases in the amount and evenness of behaviour. These observations suggest that copying confers on cultural populations an adaptive plasticity, allowing them to respond to changing environments rapidly by drawing on a wider knowledge base.     

Social learning and the replication process: an experimental investigation

Human cultural traits typically result from a gradual process that has been described as analogous to biological evolution. This observation has led pioneering scholars to draw inspiration from population genetics to develop a rigorous and successful theoretical framework of cultural evolution. Social learning, the mechanism allowing information to be transmitted between individuals, has thus been described as a simple replication mechanism. Although useful, the extent to which this idealization appropriately describes the actual social learning events has not been carefully assessed. Here, we used a specifically developed computer task to evaluate (i) the extent to which social learning leads to the replication of an observed behaviour and (ii) the consequences it has for fitness landscape exploration. Our results show that social learning does not lead to a dichotomous choice between disregarding and replicating social information. Rather, it appeared that individuals combine and transform information coming from multiple sources to produce new solutions. As a consequence, landscape exploration was promoted by the use of social information. These results invite us to rethink the way social learning is commonly modelled and could question the validity of predictions coming from models considering this process as replicative.     

The benefits of stealing from a predator: foraging rates, predation risk, and intraspecific aggression in the kleptoparasitic spider Argyrodes antipodiana

In the trade-off between food and safety, the role of aggressiveintraspecific interactions has not been extensively examined.Here I present information on this system using a kleptoparasiticspider, Argyrodts antipodiana, and its host spider and potentialpredator, Eriophora pustulosa. A. antipodiana can feed eitherat a potentially dangerous site (the hub of its host's web withthe host), or at a relatively safe site (on food bundles aroundthe edge of the host's web). I found that A. antipodiana cangain food very quickly when feeding with the host, apparentlyby exploiting the host's ability to digest the prey. Thus A.antipodiana follows predictions based on foraging models inthat it accepts a higher predation risk at the hub because ofthe higher food payoff. A. antipodiana also aggressively competesfor access to more food. However, aggressive competition increasesthe predation risk from the host, especially at tile hub wherethe host is very close. Consequently, A. antipodiana modifiesits level of intraspecific aggressiveness in accordance withits position on the web: at the hub, where the cost of aggressionis high (due to predation risk), A. antipodiana reduces itsaggressiveness, but it is aggressive away from the hub whencompeting for food bundles. The ability of A. antipodiana tochange interaction intensity as a function of its position onthe web enables it to exploit a rich, but risky, food sourceand provides a new angle for examining food and safety tradeoffs in light of intraspecific competition for food     

Social learning and human mate preferences: a potential mechanism for generating and maintaining between-population diversity in attraction

Inspired by studies demonstrating mate-choice copying effects in non-human species, recent studies of attractiveness judgements suggest that social learning also influences human preferences. In the first part of our article, we review evidence for social learning effects on preferences in humans and other animals. In the second part, we present new empirical evidence that social learning not only influences the attractiveness of specific individuals, but can also generalize to judgements of previously unseen individuals possessing similar physical traits. The different conditions represent different populations and, once a preference arises in a population, social learning can lead to the spread of preferences within that population. In the final part of our article, we discuss the theoretical basis for, and possible impact of, biases in social learning whereby individuals may preferentially copy the choices of those with high status or better access to critical information about potential mates. Such biases could mean that the choices of a select few individuals carry the greatest weight, rapidly generating agreement in preferences within a population. Collectively, these issues suggest that social learning mechanisms encourage the spread of preferences for certain traits once they arise within a population and so may explain certain cross-cultural differences.     

Social learning of predators in the dark: understanding the role of visual,chemical and mechanical information

The ability of prey to observe and learn to recognize potential predators from the behaviour of nearby individuals can dramatically increase survival and, not surprisingly, is widespread across animal taxa. A range of sensory modalities are available for this learning, with visual and chemical cues being well-established modes of transmission in aquatic systems. The use of other sensory cues in mediating social learning in fishes, including mechano-sensory cues, remains unexplored. Here, we examine the role of different sensory cues in social learning of predator recognition, using juvenile damselfish (Amphiprion percula). Specifically, we show that a predator-naive observer can socially learn to recognize a novel predator when paired with a predator-experienced conspecific in total darkness. Furthermore, this study demonstrates that when threatened, individuals release chemical cues (known as disturbance cues) into the water. These cues induce an anti-predator response in nearby individuals; however, they do not facilitate learnt recognition of the predator. As such, another sensory modality, probably mechano-sensory in origin, is responsible for information transfer in the dark. This study highlights the diversity of sensory cues used by coral reef fishes in a social learning context.     

Trading safety for food: evidence from gut contents in roach and bleak captured at different distances offshore from their daytime littoral refuge

1. Regular diel habitat shifts in roach were detected by hydro‐acoustics in five moderately eutrophic, stratifying (maximum depth 24–27 m) and approximately circular lakes (of surface area 15, 75, 125, 300 and 900 ha and diameters 250, 600, 1000, 1700 and 2600 m) in north‐eastern Poland in the years 1998–2000, when the lakes were free of smelt and other typical offshore planktivores, and their offshore areas were completely free of fish during the day. 2. The diel change in roach distribution was shown to assume a similar pattern in each lake: fish migrated from a daytime littoral refuge towards the centre of the lake at dusk, and returned to the littoral refuge at dawn. After sunset, fish gradually dispersed offshore until they covered the entire lake area in each of the three smaller lakes. In each of the two larger lakes, only small numbers of fish were seen in the central area at night, implying that the centre of the lake retained high food availability throughout the summer. 3. Inshore–offshore gradients in zooplankton prey density, body size, and numbers of eggs per clutch were weak or undetectable in the two smallest lakes, but strong and persistent in the three larger lakes, with Daphnia densities 5–30 times as high and body length 1.2–1.5 times as great in the central area as inshore. 4. The likely increase in the potential predation risk with distance from the littoral daytime refuge was found to be compensated by increased food gains in those fish which moved offshore at dusk to feed within a short time window, when light intensity was lower to make the risk reduced, but still high enough to see zooplankton prey. The benefit because of increased prey acquisition was greatest in the centre of the largest lake (at 1300 m from the shore), as revealed from gut inspections of roach and bleak trawl‐sampled at different distances from the edge of the reed belt, and seen as a gradual, order‐of‐magnitude increase in the volume of food in the foregut, The food volume against distance‐from‐shore regression was highly significant on each of the four sampling dates in the largest lake, in spite of the wide variability of food volume in individual fish.