Spotlight
Why personality differences matter for social functioning and social structure Max Wolf and Jens Krause Department of Biology and Ecology of Fishes, Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Mueggelseedamm 310, 12587 Berlin, Germany
We outline three main ways how personality differences can affect social functioning and social structure. By highlighting the broad and significant consequences that personality differences can have for social processes, our article might serve as a starting point for a research focus that aims at a systematic understanding of these consequences.
Personality differences and social processes: a two-way interaction Personality differences, between-individual differences in behaviour that are consistent over time, are widespread in the animal kingdom. Over the last years, much research has focussed on the ecological and evolutionary causes of such differences. A key result of this research is that a variety of social processes such as frequency-dependent selection, reputation-building, or social niche specialisation have been found to be important factors causing the emergence of personality differences within populations [1]. However, this is only one side of the coin. While social processes can cause personality differences, the existence of personality differences can be expected to have substantial consequences for social processes within animal groups and populations. In our view, this latter issue has received far too little attention in the past. What are the consequences of personality differences for social functioning and social structure? We here provide a first conceptual framework for a research focus centred on this question. In particular, we outline three main ways in which personality differences can affect social processes at different levels of social organisation (see Table 1 for a brief summary). Social responsiveness, behavioural coordination and social competition Firstly, the presence of personality differences within groups and populations is predicted to promote the emergence of socially responsive individuals, that is, individuals that adjust their behaviour in response to the past behaviour (or reputation) of their interaction partners. The presence of socially responsive individuals, in turn, can increase both the degree of behavioural coordination and the level of social competition within groups and Corresponding author: Wolf, M. ([email protected]). Keywords: individual differences; social responsiveness; coordination; social competition; swarm intelligence; social network. 0169-5347/ ß 2014 Published by Elsevier Ltd. http://dx.doi.org/10.1016/j.tree.2014.03.008
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populations. While a series of recent theoretical models has investigated this link between personality differences, social responsiveness and social functioning, to date little is known about this relationship in natural systems. We here provide a brief summary of the main theoretical predictions. One key prediction from a series of different models is that, in a range of contexts including aggressive and cooperative interactions, the existence of personality differences selects for socially responsive individuals [2,3]. The logic underlying this prediction is as follows. When choosing an action, a socially responsive individual takes into account the past behaviour (or reputation) of its interaction partners. Social responsiveness is thus predicted to be particularly beneficial when (i) different interaction partners differ in their behaviour, since this makes it beneficial to fine-tune the behaviour to particular interaction partners and (ii) when such differences are consistent over time, since this allows a socially responsive individual to use past behaviour as a predictor for future behaviour. The presence of socially responsive individuals, in turn, is predicted to increase the levels of behavioural coordination within groups and populations, since socially responsive individuals match their behaviour to the behaviour of their interaction partners. In situations where individuals within a group have the choice between taking the lead or following, for example, the presence of socially responsive individuals can promote a high degree of coordinated behaviour among individuals within that group [4]. In hawk-dove like contest situations, the presence of socially responsive individuals can increase the frequency of ‘coordinated’ hawk-dove interactions, and decrease the frequency of ‘uncoordinated’ hawk-hawk and dove-dove interactions [2]. The presence of socially responsive individuals is also predicted to increase social competition within groups and populations. This is caused by the fact that socially responsive individuals might interrupt an interaction and look for a new interaction partner. This implicit threat inherent in interactions with socially responsive individuals puts pressure on their interaction partners which, in turn, can give rise to social outcomes that differ substantially from those achieved in the absence of socially responsive individuals [3]. In the context of cooperation, for example, the presence of socially responsive individuals can give rise to high levels of cooperation in situations where very little cooperation is expected in the absence of socially responsive individuals [3].
Spotlight
Trends in Ecology & Evolution June 2014, Vol. 29, No. 6
Table 1. Three main ways how personality differences can affect social functioning and social structure at different levels of social organisation Aspect Social responsiveness, behavioural coordination and social competition
Problem-solving ability
Social structure
Implications Personality differences select for socially responsive individuals. The presence of socially responsive individuals, in turn, is predicted to (i) increase the levels of behavioural coordination within groups and populations, (ii) increase the social competition within groups and populations, thereby giving rise to social outcomes (e.g., high levels of cooperation) that differ substantially from those achieved in the absence of socially responsive individuals. (i) ‘Pool of competence hypothesis’: the more diverse a group, the more likely it is to harbour the specialist for any given problem. (ii) Personality differences are associated with differences in experience, information acquisition and/or information use. Such differences can promote the ability of groups to make use of swarm intelligence. (iii) Personality differences can give rise to communication problems and in-group/out-group categorization processes hampering group performance. Personality types differ in the number and the frequency of interactions with others, the responsiveness to previous social experiences and their preferred social interaction partners. As a consequence of these differences, the composition of personality types within a group or population can have substantial consequences for the emerging social fine structure.
Problem-solving ability Secondly, personality differences can be expected to affect the problem-solving ability of groups. Different personality types often differ in their relative ability to solve different ecological problems. In fish, birds and rodents, for example, proactive types tend to outperform reactive types under stable environmental conditions, whereas reactive types outperform proactive types under changing environmental conditions [5]. Analogous context-dependent differences in the relative performance of personality types can be expected to be present in many other contexts. Consequently, for any given ecological problem, the more diverse a group, the higher its chance that it harbours the specialist for that problem (‘pool of competence hypothesis’ [6]). If a group can capitalize on this pool of abilities (e.g., via social learning), more diverse groups should thus be better problem solvers than less diverse groups; first evidence in birds is in line with this hypothesis [6]. The presence of personality differences might also affect the ability of groups to develop swarm intelligence (aka collective intelligence and wisdom of the crowd). In brief, swarm intelligence occurs whenever for a given cognitive problem a group can outperform even the best of its members [7]. Importantly, many of the mechanisms underlying swarm intelligence require that individuals differ in their experience and/or in the way they acquire or evaluate information [7]. Put simply, whenever individuals within a group are too similar, the swarm intelligence potential is diminished. Personality differences can be expected to be an important source of this required between-individual variation, since different personality types often differ systematically in experience, information acquisition and information use [5]. The presence of different personality types within a group might thus be a key factor promoting the ability of that group to make use of swarm intelligence. To the best of our knowledge, this link between personality differences and swarm intelligence remains largely unexplored in the animal literature. Before moving on, we stress that the existence of personality differences might not only have positive effects on the problem-solving ability of groups. In humans, for example, between-individual diversity can give rise to communication problems and in-group/out-group categorization processes,
Refs [2–4]
[6–8]
[9–11]
hampering group performance [8]; similarly, between-individual diversity might weaken group cohesion in many nonhuman species, thereby decreasing performance in tasks where cohesion is important. Social structure Thirdly, personality differences can be expected to be an important factor underlying the emerging social fine structure (i.e., social interaction network) within groups and populations. Personality types differ in the number and the frequency of interactions with others, the responsiveness to previous social experiences, and their preferred interaction partners [1,5]. As a consequence, the composition of personality types within a group or population can be expected to be a key determinant of its emerging social fine structure. To date, few studies in the animal literature have explicitly addressed this potentially important relationship between personality types and social fine structure. In one of these studies, bold sticklebacks, Gasterosteus aculeatus, have been shown to have fewer interaction than their shy conspecifics, but to distribute these interactions more evenly across all group members [9]. Shy individuals, in contrast, associated preferentially with a small number of other group members. As a result, groups composed of bold individuals were characterized by a relatively low number of interactions and a uniform distribution of these interactions whereas groups of shy individuals were characterized by more long-lasting associations between individuals and highly non-uniform interaction distributions. Different personality types differ consistently in their responsiveness to previous social experiences. Whether or not individuals in a group or population respond to previous social experiences (e.g., via breaking interactions), and how frequent such responsive individuals are, can have substantial consequences for social network dynamics and the emerging social fine structure. For example, in an experiment with humans, when given the chance to break interaction links, compared to a situation where individuals could not break interaction links, highly clustered networks emerged which, in turn, promoted high levels of cooperation [10]. Personality types might also differ in their preferred social interaction partners. Homophily, for example, refers 307
Spotlight to the observation that humans tend to associate with others that are similar to themselves. Such systematic differences in partner preferences, in turn, can give rise to non-random mixing of individuals in social networks and assortment based on personality types, a phenomenon that has been observed in a wild population of Trinidadian guppies, Poecilia reticulata [11]. To sum up, we have discussed three main ways in which the existence of personality differences can affect the social functioning and the social structure of groups and populations. While certainly not being comprehensive, the above discussion highlights the broad and significant consequences that personality differences can have for social processes and we hope that our article serves as a starting point for a research focus that aims at a systematic understanding of these consequences. Acknowledgments We thank Paul Craze and two anonymous reviewers for constructive criticism and valuable comments, we also thank the participants of the Symposium ‘Personality: causes and consequences of consistent behavioural variation’ and the Volkswagen Foundation for funding this Symposium. This work was part of the B-Types project funded through the Leibniz Competition (SAW-2013-IGB-2).
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References 1 Wolf, M. and Weissing, F.J. (2010) An explanatory framework for adaptive personality differences. Phil. Trans. R. Soc. B 365, 3959–3968 2 Wolf, M. et al. (2011) On the coevolution of social responsiveness and behavioural consistency. Proc. R. Soc. B 278, 440–448 3 McNamara, J.M. and Leimar, O. (2010) Variation and the response to variation as a basis for successful cooperation. Phil. Trans. R. Soc. B 365, 2627–2633 4 Johnstone, R.A. and Manica, A. (2011) Evolution of personality differences in leadership. Proc. Natl. Acad. Sci. U.S.A. 108, 8373– 8378 5 Coppens, C.M. et al. (2010) Coping styles and behavioural flexibility: towards underlying mechanisms. Phil. Trans. R. Soc. B 365, 4021– 4028 6 Morand-Ferron, J. and Quinn, J.L. (2011) Larger groups of passerines are more efficient problem solvers in the wild. Proc. Natl. Acad. Sci. U.S.A. 108, 15898–15903 7 Krause, J. et al. (2010) Swarm intelligence in animals and humans. Trends Ecol. Evol. 25, 28–34 8 Van Knippenberg, D. and Schippers, M.C. (2007) Work group diversity. Annu. Rev. Psychol. 58, 515–541 9 Pike, T.W. et al. (2008) Behavioural phenotype affects social interactions in an animal network. Proc. R. Soc. B 275, 2515–2520 10 Fehl, K. et al. (2011) Co-evolution of behaviour and social network structure promotes human cooperation. Ecol. Lett. 14, 546–551 11 Croft, D.P. et al. (2009) Behavioural trait assortment in a social network: patterns and implications. Behav. Ecol. Sociobiol. 63, 1495–1503
Why personality differences matter for social functioning and social structure Max Wolf and Jens Krause Department of Biology and Ecology of Fishes, Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Mueggelseedamm 310, 12587 Berlin, Germany
We outline three main ways how personality differences can affect social functioning and social structure. By highlighting the broad and significant consequences that personality differences can have for social processes, our article might serve as a starting point for a research focus that aims at a systematic understanding of these consequences.
Personality differences and social processes: a two-way interaction Personality differences, between-individual differences in behaviour that are consistent over time, are widespread in the animal kingdom. Over the last years, much research has focussed on the ecological and evolutionary causes of such differences. A key result of this research is that a variety of social processes such as frequency-dependent selection, reputation-building, or social niche specialisation have been found to be important factors causing the emergence of personality differences within populations [1]. However, this is only one side of the coin. While social processes can cause personality differences, the existence of personality differences can be expected to have substantial consequences for social processes within animal groups and populations. In our view, this latter issue has received far too little attention in the past. What are the consequences of personality differences for social functioning and social structure? We here provide a first conceptual framework for a research focus centred on this question. In particular, we outline three main ways in which personality differences can affect social processes at different levels of social organisation (see Table 1 for a brief summary). Social responsiveness, behavioural coordination and social competition Firstly, the presence of personality differences within groups and populations is predicted to promote the emergence of socially responsive individuals, that is, individuals that adjust their behaviour in response to the past behaviour (or reputation) of their interaction partners. The presence of socially responsive individuals, in turn, can increase both the degree of behavioural coordination and the level of social competition within groups and Corresponding author: Wolf, M. ([email protected]). Keywords: individual differences; social responsiveness; coordination; social competition; swarm intelligence; social network. 0169-5347/ ß 2014 Published by Elsevier Ltd. http://dx.doi.org/10.1016/j.tree.2014.03.008
306
Trends in Ecology & Evolution, June 2014, Vol. 29, No. 6
populations. While a series of recent theoretical models has investigated this link between personality differences, social responsiveness and social functioning, to date little is known about this relationship in natural systems. We here provide a brief summary of the main theoretical predictions. One key prediction from a series of different models is that, in a range of contexts including aggressive and cooperative interactions, the existence of personality differences selects for socially responsive individuals [2,3]. The logic underlying this prediction is as follows. When choosing an action, a socially responsive individual takes into account the past behaviour (or reputation) of its interaction partners. Social responsiveness is thus predicted to be particularly beneficial when (i) different interaction partners differ in their behaviour, since this makes it beneficial to fine-tune the behaviour to particular interaction partners and (ii) when such differences are consistent over time, since this allows a socially responsive individual to use past behaviour as a predictor for future behaviour. The presence of socially responsive individuals, in turn, is predicted to increase the levels of behavioural coordination within groups and populations, since socially responsive individuals match their behaviour to the behaviour of their interaction partners. In situations where individuals within a group have the choice between taking the lead or following, for example, the presence of socially responsive individuals can promote a high degree of coordinated behaviour among individuals within that group [4]. In hawk-dove like contest situations, the presence of socially responsive individuals can increase the frequency of ‘coordinated’ hawk-dove interactions, and decrease the frequency of ‘uncoordinated’ hawk-hawk and dove-dove interactions [2]. The presence of socially responsive individuals is also predicted to increase social competition within groups and populations. This is caused by the fact that socially responsive individuals might interrupt an interaction and look for a new interaction partner. This implicit threat inherent in interactions with socially responsive individuals puts pressure on their interaction partners which, in turn, can give rise to social outcomes that differ substantially from those achieved in the absence of socially responsive individuals [3]. In the context of cooperation, for example, the presence of socially responsive individuals can give rise to high levels of cooperation in situations where very little cooperation is expected in the absence of socially responsive individuals [3].
Spotlight
Trends in Ecology & Evolution June 2014, Vol. 29, No. 6
Table 1. Three main ways how personality differences can affect social functioning and social structure at different levels of social organisation Aspect Social responsiveness, behavioural coordination and social competition
Problem-solving ability
Social structure
Implications Personality differences select for socially responsive individuals. The presence of socially responsive individuals, in turn, is predicted to (i) increase the levels of behavioural coordination within groups and populations, (ii) increase the social competition within groups and populations, thereby giving rise to social outcomes (e.g., high levels of cooperation) that differ substantially from those achieved in the absence of socially responsive individuals. (i) ‘Pool of competence hypothesis’: the more diverse a group, the more likely it is to harbour the specialist for any given problem. (ii) Personality differences are associated with differences in experience, information acquisition and/or information use. Such differences can promote the ability of groups to make use of swarm intelligence. (iii) Personality differences can give rise to communication problems and in-group/out-group categorization processes hampering group performance. Personality types differ in the number and the frequency of interactions with others, the responsiveness to previous social experiences and their preferred social interaction partners. As a consequence of these differences, the composition of personality types within a group or population can have substantial consequences for the emerging social fine structure.
Problem-solving ability Secondly, personality differences can be expected to affect the problem-solving ability of groups. Different personality types often differ in their relative ability to solve different ecological problems. In fish, birds and rodents, for example, proactive types tend to outperform reactive types under stable environmental conditions, whereas reactive types outperform proactive types under changing environmental conditions [5]. Analogous context-dependent differences in the relative performance of personality types can be expected to be present in many other contexts. Consequently, for any given ecological problem, the more diverse a group, the higher its chance that it harbours the specialist for that problem (‘pool of competence hypothesis’ [6]). If a group can capitalize on this pool of abilities (e.g., via social learning), more diverse groups should thus be better problem solvers than less diverse groups; first evidence in birds is in line with this hypothesis [6]. The presence of personality differences might also affect the ability of groups to develop swarm intelligence (aka collective intelligence and wisdom of the crowd). In brief, swarm intelligence occurs whenever for a given cognitive problem a group can outperform even the best of its members [7]. Importantly, many of the mechanisms underlying swarm intelligence require that individuals differ in their experience and/or in the way they acquire or evaluate information [7]. Put simply, whenever individuals within a group are too similar, the swarm intelligence potential is diminished. Personality differences can be expected to be an important source of this required between-individual variation, since different personality types often differ systematically in experience, information acquisition and information use [5]. The presence of different personality types within a group might thus be a key factor promoting the ability of that group to make use of swarm intelligence. To the best of our knowledge, this link between personality differences and swarm intelligence remains largely unexplored in the animal literature. Before moving on, we stress that the existence of personality differences might not only have positive effects on the problem-solving ability of groups. In humans, for example, between-individual diversity can give rise to communication problems and in-group/out-group categorization processes,
Refs [2–4]
[6–8]
[9–11]
hampering group performance [8]; similarly, between-individual diversity might weaken group cohesion in many nonhuman species, thereby decreasing performance in tasks where cohesion is important. Social structure Thirdly, personality differences can be expected to be an important factor underlying the emerging social fine structure (i.e., social interaction network) within groups and populations. Personality types differ in the number and the frequency of interactions with others, the responsiveness to previous social experiences, and their preferred interaction partners [1,5]. As a consequence, the composition of personality types within a group or population can be expected to be a key determinant of its emerging social fine structure. To date, few studies in the animal literature have explicitly addressed this potentially important relationship between personality types and social fine structure. In one of these studies, bold sticklebacks, Gasterosteus aculeatus, have been shown to have fewer interaction than their shy conspecifics, but to distribute these interactions more evenly across all group members [9]. Shy individuals, in contrast, associated preferentially with a small number of other group members. As a result, groups composed of bold individuals were characterized by a relatively low number of interactions and a uniform distribution of these interactions whereas groups of shy individuals were characterized by more long-lasting associations between individuals and highly non-uniform interaction distributions. Different personality types differ consistently in their responsiveness to previous social experiences. Whether or not individuals in a group or population respond to previous social experiences (e.g., via breaking interactions), and how frequent such responsive individuals are, can have substantial consequences for social network dynamics and the emerging social fine structure. For example, in an experiment with humans, when given the chance to break interaction links, compared to a situation where individuals could not break interaction links, highly clustered networks emerged which, in turn, promoted high levels of cooperation [10]. Personality types might also differ in their preferred social interaction partners. Homophily, for example, refers 307
Spotlight to the observation that humans tend to associate with others that are similar to themselves. Such systematic differences in partner preferences, in turn, can give rise to non-random mixing of individuals in social networks and assortment based on personality types, a phenomenon that has been observed in a wild population of Trinidadian guppies, Poecilia reticulata [11]. To sum up, we have discussed three main ways in which the existence of personality differences can affect the social functioning and the social structure of groups and populations. While certainly not being comprehensive, the above discussion highlights the broad and significant consequences that personality differences can have for social processes and we hope that our article serves as a starting point for a research focus that aims at a systematic understanding of these consequences. Acknowledgments We thank Paul Craze and two anonymous reviewers for constructive criticism and valuable comments, we also thank the participants of the Symposium ‘Personality: causes and consequences of consistent behavioural variation’ and the Volkswagen Foundation for funding this Symposium. This work was part of the B-Types project funded through the Leibniz Competition (SAW-2013-IGB-2).
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References 1 Wolf, M. and Weissing, F.J. (2010) An explanatory framework for adaptive personality differences. Phil. Trans. R. Soc. B 365, 3959–3968 2 Wolf, M. et al. (2011) On the coevolution of social responsiveness and behavioural consistency. Proc. R. Soc. B 278, 440–448 3 McNamara, J.M. and Leimar, O. (2010) Variation and the response to variation as a basis for successful cooperation. Phil. Trans. R. Soc. B 365, 2627–2633 4 Johnstone, R.A. and Manica, A. (2011) Evolution of personality differences in leadership. Proc. Natl. Acad. Sci. U.S.A. 108, 8373– 8378 5 Coppens, C.M. et al. (2010) Coping styles and behavioural flexibility: towards underlying mechanisms. Phil. Trans. R. Soc. B 365, 4021– 4028 6 Morand-Ferron, J. and Quinn, J.L. (2011) Larger groups of passerines are more efficient problem solvers in the wild. Proc. Natl. Acad. Sci. U.S.A. 108, 15898–15903 7 Krause, J. et al. (2010) Swarm intelligence in animals and humans. Trends Ecol. Evol. 25, 28–34 8 Van Knippenberg, D. and Schippers, M.C. (2007) Work group diversity. Annu. Rev. Psychol. 58, 515–541 9 Pike, T.W. et al. (2008) Behavioural phenotype affects social interactions in an animal network. Proc. R. Soc. B 275, 2515–2520 10 Fehl, K. et al. (2011) Co-evolution of behaviour and social network structure promotes human cooperation. Ecol. Lett. 14, 546–551 11 Croft, D.P. et al. (2009) Behavioural trait assortment in a social network: patterns and implications. Behav. Ecol. Sociobiol. 63, 1495–1503
