- Email: [email protected]
Group decision-making in fission–fusion societies
Behavioural Processes 84 (2010) 662–663
Contents lists available at ScienceDirect
Behavioural Processes journal homepage: www.elsevier.com/locate/behavproc
Group decision-making in fission–fusion societies Gerald Kerth a,b,∗ a b
Zoologisches Institut, Universität Zurich, Winterthurerstrasse, 190, CH-8057 Zurich, Switzerland Max-Planck-Institute for Ornithology, D-82319 Seewiesen, Germany
a r t i c l e
i n f o
Article history: Received 18 January 2010 Accepted 25 February 2010 Keywords: Bat Fission–fusion Group-decisions Sociality
a b s t r a c t The prevalent view of group splitting during group decisions is that a beneficial consensus has not been reached because time constraints, different individual information, or inter-individual conflicts lead to fission instead of a compromise. However, societies with high fission–fusion dynamics may allow their members to avoid consensus decisions that are not in their favour without foregoing grouping benefits that arise from collective behaviour. Moreover, by forming temporary subgroups that represent individual preferences better than the group as a whole fission–fusion societies could avoid a permanent break up even in situations where conflicts among their members are to strong to reach a consensus. © 2010 Elsevier B.V. All rights reserved.
The spatial and temporal dynamics of animal societies vary between species, ranging from complete cohesiveness to high fission–fusion dynamics. Societies with high fission–fusion dynamics are characterized by regular splitting into temporary subgroups, which places them among the most dynamic of all animal societies. Fission–fusion behaviour is widespread among animals, and complex multi-level fission–fusion societies occur in several mammals, including humans (Aureli et al., 2008). How members of fission–fusion societies coordinate their behaviour however is still largely unknown as most empirical and theoretical studies on group decision-making did not investigate the option of splitting into temporary subgroups, or treated it as a maladaptive outcome. In their seminal review, Conradt and Roper (2005) argued that a conceptual difference exists between consensus decisions, which occur in groups that maintain cohesion, and combined decisions, which occur in groups that can temporarily split into smaller subunits. Accordingly, most of the models dealing with animal group decision-making assume that individuals only gain grouping benefits if all of them obey to the same decision and stay within one group (Conradt and Roper, 2003, 2007; Rands et al., 2003; Couzin et al., 2005). This assumption is fully justified for many eusocial insects, such as honeybees and many ants. If they have only one queen, eusocial insect colonies depend on consensus decisions, for example when moving to a new nest site, because their members receive (indirect) fitness benefits only if they stay with their queen (e.g. Seeley, 2003). But in many other social species, including humans, where groups contain multiple breeders, the assumption
∗ Correspondence address: Max-Planck-Institute for Ornithology, D-82319 Seewiesen, Germany. E-mail address: [email protected]. 0376-6357/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.beproc.2010.02.023
that group cohesion is always required for gaining full grouping benefits is probably not met. Currently the prevalent view of group splitting during group decisions is that a beneficial consensus has not been reached because time constraints, different individual information, or interindividual conflicts lead to fission instead of a compromise (Franks et al., 2003; Conradt and Roper, 2003, 2005, 2009). However, it seems also possible that splitting into subgroups is an optimal outcome of a group decision, for example if it is best for all individuals to temporarily forage or rest in smaller subgroups (Kerth et al., 2006). It will depend on the shape of the function describing the relationship between the grouping benefits and the size of a group whether individuals in subgroups can still gain the full range of grouping benefits. In bats, for example, grouping benefits that arise from social thermoregulation do not increase linearly with group size but level off when a group reaches a certain size (Pretzlaff et al., 2010). Similar non-linear relationships between grouping benefits and group sizes are probably widespread in social species. Several recent empirical studies on group decision-making in bats and primates show that inter-individual conflicts can lead to temporary group fission instead of a consensus decision without risking permanent group fission (Kerth et al., 2006; King et al., 2008). In chacma baboons (Papioursinus) temporary group fission can occur if there is a conflict between high and low ranking individuals over the decision where to feed (King et al., 2008). In Bechstein’s bats (Myotis bechsteinii) that daily make group decisions about communal day roosts, colony fission can occur in situations where individuals differ in their information about the quality of novel roosts (Kerth et al., 2006). Similarly, in domestic pigeons (Columba livia f. domestica) that make group decisions about travel routes, group fission occurs if individuals differ strongly between their preferred individual routes (Biro et al., 2006).
G. Kerth / Behavioural Processes 84 (2010) 662–663
In Bechstein’s bats and chacma baboons, group members can avoid group decisions that are against their individual interest by temporarily splitting into smaller subgroups that later merge again. Nevertheless, they often do achieve a consensus, which at least in Bechstein’s bats reflects the information or interests available to the majority of the group members (Kerth et al., 2006; King et al., 2008; Stueckle and Zinner, 2008). This suggests that group decision-making processes in fission–fusion societies are not fundamentally different from those in cohesive animal societies that depend more strongly on reaching a consensus. To settle the question, whether group decisions in fission–fusion societies differ from those in cohesive groups, more studies on group decision-making in fission–fusion societies are needed as currently most studies deal with group decision-making in cohesive animal societies (Conradt and Roper, 2005; Kerth et al., 2006; Kerth, 2010). Increasing evidence for highly flexible group decisions within a given species suggests that at least for many vertebrate societies the outcome of a group decision (fission versus cohesion) depends on the ratio of grouping benefits versus consensus costs in each situation (Biro et al., 2006; Kerth et al., 2006; King et al., 2008; Conradt and Roper, 2009; Kerth, 2010). Fission–fusion societies allow their members to avoid consensus decisions that are not in their favour without foregoing grouping benefits that arise from collective behaviour, such as social thermoregulation in bats (Kerth et al., 2006; Kerth, 2008; Pretzlaff et al., 2010). By forming temporary subgroups that represent individual preferences better than the group as a whole fission–fusion societies avoid a permanent break even in situations where conflicts among their members are to strong to reach a consensus. This is something we know well from our own societies: if you cannot reach a compromise a temporary splitting of groups is better than a permanent break up.
663
References Aureli, F., Schaffner, C.M., Boesch, C., et al., 2008. Fission–fusion dynamics: new research frameworks. Curr. Anthropol. 49, 627–654. Biro, D., Sumpter, D.J.T., Meade, J., et al., 2006. From compromise to leadership in pigeon homing. Curr. Biol. 16, 2123–2128. Conradt, L., Roper, T.J., 2003. Group decision-making in animals. Nature 421, 155–158. Conradt, L., Roper, T.J., 2005. Consensus decision making in animals. Trends Ecol. Evol. 20, 449–456. Conradt, L., Roper, T.J., 2007. Democracy in animals: the evolution of shared group decisions. Proc. R. Soc. Lond. B 274, 2317–2326. Conradt, L., Roper, T.J., 2009. Conflicts of interest and the evolution of decision sharing. Phil. Trans. R. Soc. B 364, 807–819. Couzin, I.D., Krause, J., Franks, N.R., et al., 2005. Effective leadership and decisionmaking in animal groups on the move. Nature 433, 513–516. Franks, N.R., Dornhaus, A., Fitzsimmons, J.P., et al., 2003. Speed versus accuracy in collective decision making. Proc. R. Soc. Lond. B 270, 2457–2463. Kerth, G, 2008. Causes and consequences of sociality in bats. BioScience 58, 737–755. Kerth, G., 2010. Group decision-making in animal societies, Kappeler (Ed.), Behavior: Evolution & Mechanisms, Springer Verlag. Kerth, G., Ebert, C., Schmidtke C, 2006. Group decision-making in fission–fusion societies: evidence from two field experiments in Bechstein’s bats. Proc. R. Soc. Lond. B 273, 2785–2790. King, A.J., Douglas, C.M.S., Huchard, E., et al., 2008. Dominance and affiliation mediate despotism in a social primate. Curr. Biol. 18, 1833–1838. Pretzlaff, I., Kerth, G., Dausmann, K.H., 2010. Communally breeding bats use physiological and behavioural adjustments to optimise daily energy expenditure. Naturwissenschaften 97, 353–363. Rands, S.A., Cowlishaw, G., Pettifor, R.A., et al., 2003. Spontaneous emergence of leaders and followers in foraging pairs. Nature 423, 432–434. Seeley, T.D., 2003. Consensus building during nest-site selection in honey bee swarms: the expiration of dissent. Behav. Ecol. Sociobiol. 53, 417–424. Stueckle, S., Zinner, D., 2008. To follow or not to follow: decision making and leadership during the morning departure in chacma baboons. Anim. Behav. 75, 1995–2004.
Contents lists available at ScienceDirect
Behavioural Processes journal homepage: www.elsevier.com/locate/behavproc
Group decision-making in fission–fusion societies Gerald Kerth a,b,∗ a b
Zoologisches Institut, Universität Zurich, Winterthurerstrasse, 190, CH-8057 Zurich, Switzerland Max-Planck-Institute for Ornithology, D-82319 Seewiesen, Germany
a r t i c l e
i n f o
Article history: Received 18 January 2010 Accepted 25 February 2010 Keywords: Bat Fission–fusion Group-decisions Sociality
a b s t r a c t The prevalent view of group splitting during group decisions is that a beneficial consensus has not been reached because time constraints, different individual information, or inter-individual conflicts lead to fission instead of a compromise. However, societies with high fission–fusion dynamics may allow their members to avoid consensus decisions that are not in their favour without foregoing grouping benefits that arise from collective behaviour. Moreover, by forming temporary subgroups that represent individual preferences better than the group as a whole fission–fusion societies could avoid a permanent break up even in situations where conflicts among their members are to strong to reach a consensus. © 2010 Elsevier B.V. All rights reserved.
The spatial and temporal dynamics of animal societies vary between species, ranging from complete cohesiveness to high fission–fusion dynamics. Societies with high fission–fusion dynamics are characterized by regular splitting into temporary subgroups, which places them among the most dynamic of all animal societies. Fission–fusion behaviour is widespread among animals, and complex multi-level fission–fusion societies occur in several mammals, including humans (Aureli et al., 2008). How members of fission–fusion societies coordinate their behaviour however is still largely unknown as most empirical and theoretical studies on group decision-making did not investigate the option of splitting into temporary subgroups, or treated it as a maladaptive outcome. In their seminal review, Conradt and Roper (2005) argued that a conceptual difference exists between consensus decisions, which occur in groups that maintain cohesion, and combined decisions, which occur in groups that can temporarily split into smaller subunits. Accordingly, most of the models dealing with animal group decision-making assume that individuals only gain grouping benefits if all of them obey to the same decision and stay within one group (Conradt and Roper, 2003, 2007; Rands et al., 2003; Couzin et al., 2005). This assumption is fully justified for many eusocial insects, such as honeybees and many ants. If they have only one queen, eusocial insect colonies depend on consensus decisions, for example when moving to a new nest site, because their members receive (indirect) fitness benefits only if they stay with their queen (e.g. Seeley, 2003). But in many other social species, including humans, where groups contain multiple breeders, the assumption
∗ Correspondence address: Max-Planck-Institute for Ornithology, D-82319 Seewiesen, Germany. E-mail address: [email protected]. 0376-6357/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.beproc.2010.02.023
that group cohesion is always required for gaining full grouping benefits is probably not met. Currently the prevalent view of group splitting during group decisions is that a beneficial consensus has not been reached because time constraints, different individual information, or interindividual conflicts lead to fission instead of a compromise (Franks et al., 2003; Conradt and Roper, 2003, 2005, 2009). However, it seems also possible that splitting into subgroups is an optimal outcome of a group decision, for example if it is best for all individuals to temporarily forage or rest in smaller subgroups (Kerth et al., 2006). It will depend on the shape of the function describing the relationship between the grouping benefits and the size of a group whether individuals in subgroups can still gain the full range of grouping benefits. In bats, for example, grouping benefits that arise from social thermoregulation do not increase linearly with group size but level off when a group reaches a certain size (Pretzlaff et al., 2010). Similar non-linear relationships between grouping benefits and group sizes are probably widespread in social species. Several recent empirical studies on group decision-making in bats and primates show that inter-individual conflicts can lead to temporary group fission instead of a consensus decision without risking permanent group fission (Kerth et al., 2006; King et al., 2008). In chacma baboons (Papioursinus) temporary group fission can occur if there is a conflict between high and low ranking individuals over the decision where to feed (King et al., 2008). In Bechstein’s bats (Myotis bechsteinii) that daily make group decisions about communal day roosts, colony fission can occur in situations where individuals differ in their information about the quality of novel roosts (Kerth et al., 2006). Similarly, in domestic pigeons (Columba livia f. domestica) that make group decisions about travel routes, group fission occurs if individuals differ strongly between their preferred individual routes (Biro et al., 2006).
G. Kerth / Behavioural Processes 84 (2010) 662–663
In Bechstein’s bats and chacma baboons, group members can avoid group decisions that are against their individual interest by temporarily splitting into smaller subgroups that later merge again. Nevertheless, they often do achieve a consensus, which at least in Bechstein’s bats reflects the information or interests available to the majority of the group members (Kerth et al., 2006; King et al., 2008; Stueckle and Zinner, 2008). This suggests that group decision-making processes in fission–fusion societies are not fundamentally different from those in cohesive animal societies that depend more strongly on reaching a consensus. To settle the question, whether group decisions in fission–fusion societies differ from those in cohesive groups, more studies on group decision-making in fission–fusion societies are needed as currently most studies deal with group decision-making in cohesive animal societies (Conradt and Roper, 2005; Kerth et al., 2006; Kerth, 2010). Increasing evidence for highly flexible group decisions within a given species suggests that at least for many vertebrate societies the outcome of a group decision (fission versus cohesion) depends on the ratio of grouping benefits versus consensus costs in each situation (Biro et al., 2006; Kerth et al., 2006; King et al., 2008; Conradt and Roper, 2009; Kerth, 2010). Fission–fusion societies allow their members to avoid consensus decisions that are not in their favour without foregoing grouping benefits that arise from collective behaviour, such as social thermoregulation in bats (Kerth et al., 2006; Kerth, 2008; Pretzlaff et al., 2010). By forming temporary subgroups that represent individual preferences better than the group as a whole fission–fusion societies avoid a permanent break even in situations where conflicts among their members are to strong to reach a consensus. This is something we know well from our own societies: if you cannot reach a compromise a temporary splitting of groups is better than a permanent break up.
663
References Aureli, F., Schaffner, C.M., Boesch, C., et al., 2008. Fission–fusion dynamics: new research frameworks. Curr. Anthropol. 49, 627–654. Biro, D., Sumpter, D.J.T., Meade, J., et al., 2006. From compromise to leadership in pigeon homing. Curr. Biol. 16, 2123–2128. Conradt, L., Roper, T.J., 2003. Group decision-making in animals. Nature 421, 155–158. Conradt, L., Roper, T.J., 2005. Consensus decision making in animals. Trends Ecol. Evol. 20, 449–456. Conradt, L., Roper, T.J., 2007. Democracy in animals: the evolution of shared group decisions. Proc. R. Soc. Lond. B 274, 2317–2326. Conradt, L., Roper, T.J., 2009. Conflicts of interest and the evolution of decision sharing. Phil. Trans. R. Soc. B 364, 807–819. Couzin, I.D., Krause, J., Franks, N.R., et al., 2005. Effective leadership and decisionmaking in animal groups on the move. Nature 433, 513–516. Franks, N.R., Dornhaus, A., Fitzsimmons, J.P., et al., 2003. Speed versus accuracy in collective decision making. Proc. R. Soc. Lond. B 270, 2457–2463. Kerth, G, 2008. Causes and consequences of sociality in bats. BioScience 58, 737–755. Kerth, G., 2010. Group decision-making in animal societies, Kappeler (Ed.), Behavior: Evolution & Mechanisms, Springer Verlag. Kerth, G., Ebert, C., Schmidtke C, 2006. Group decision-making in fission–fusion societies: evidence from two field experiments in Bechstein’s bats. Proc. R. Soc. Lond. B 273, 2785–2790. King, A.J., Douglas, C.M.S., Huchard, E., et al., 2008. Dominance and affiliation mediate despotism in a social primate. Curr. Biol. 18, 1833–1838. Pretzlaff, I., Kerth, G., Dausmann, K.H., 2010. Communally breeding bats use physiological and behavioural adjustments to optimise daily energy expenditure. Naturwissenschaften 97, 353–363. Rands, S.A., Cowlishaw, G., Pettifor, R.A., et al., 2003. Spontaneous emergence of leaders and followers in foraging pairs. Nature 423, 432–434. Seeley, T.D., 2003. Consensus building during nest-site selection in honey bee swarms: the expiration of dissent. Behav. Ecol. Sociobiol. 53, 417–424. Stueckle, S., Zinner, D., 2008. To follow or not to follow: decision making and leadership during the morning departure in chacma baboons. Anim. Behav. 75, 1995–2004.