Under the superorganism concept, insect societies are so tightly integrated that they possess features analogous to those of single organisms, including collective cognition. If so, colony function ...might fruitfully be studied using methods developed to understand individual animals. Here, we review research that uses psychological approaches to understand decision making by colonies. The application of neural models to collective choice shows fundamental similarities between how brains and colonies balance speed accuracy trade-offs in decision making. Experimental analyses have explored collective rationality, cognitive capacity, and perceptual discrimination at both individual and colony levels. A major theme is the emergence of improved colony-level function from interactions among relatively less capable individuals. However, colonies also encounter performance costs due to their reliance on positive feedback, which generates consensus but can also amplify errors. Collective learning is a nascent field for the further application of psychological methods to colonies. The research strategy reviewed here shows how the superorganism concept can serve as more than an illustrative analogy.
AbstractThe nests built by social insects are complex group-level structures that emerge from interactions among individuals following simple behavioral rules. Nest patterns vary among species, and ...the theory of complex systems predicts that there is no simple one-to-one relationship between variation in collective patterns and variation in individual behaviors. Therefore, a species-by-species comparison of the actual building process is essential to understand the mechanism producing diverse nest patterns. Here, we compare tunnel formation of three termite sp ecies and reveal two mechanisms producing interspecific variation: in one, a common behavioral rule yields distinct patterns via parameter tuning, and in the other, distinct rules produce similar patterns. We found that two related species transport sand in the same way using mandibles but build tunnels with different degrees of branching. The variation arises from different probabilities of choosing between two behavioral options at crowded tunnel faces: excavating the sidewall to make a new branch or waiting for clearance to extend the current tunnel. We further discovered that a third species independently evolved low-branched patterns using different building rules, namely, a bucket brigade that can excavate a crowded tunnel. Our findings emphasize the importance of direct comparative study of collective behaviors at both individual and group levels.
Increasing the number of options can paradoxically lead to worse decisions, a phenomenon known as cognitive overload 1. This happens when an individual decision-maker attempts to digest information ...exceeding its processing capacity. Highly integrated groups, such as social insect colonies, make consensus decisions that combine the efforts of many members, suggesting that these groups can overcome individual limitations 2–4. Here we report that an ant colony choosing a new nest site is less vulnerable to cognitive overload than an isolated ant making this decision on her own. We traced this improvement to differences in individual behavior. In whole colonies, each ant assesses only a small subset of available sites, and the colony combines their efforts to thoroughly explore all options. An isolated ant, on the other hand, must personally assess a larger number of sites to approach the same level of option coverage. By sharing the burden of assessment, the colony avoids overtaxing the abilities of its members.
Search theory predicts that animals evolve efficient movement patterns to enhance encounter rates with specific targets. The optimal movements vary with the surrounding environments, which may ...explain the observation that animals often switch their movement patterns depending on conditions. However, the effectiveness of behavioural change during search is rarely evaluated because it is difficult to examine the actual encounter dynamics.
Here we studied how partner‐seeking termites update their search strategies depending on the local densities of potential mates. After a dispersal flight, termites drop their wings and walk to search for a mate; when a female and a male meet, they form a female‐led tandem pair and search for a favourable nesting site. If a pair is separated, they have two search options—reunite with their stray partner, or seek a new partner. We hypothesized that the density of individuals affects separation–reunion dynamics and thus the optimal search strategy.
We observed the searching process across different densities and found that termite pairs were often separated but obtained a new partner quickly at high mate density. After separation, while females consistently slowed down, males increased their speed according to the density. Under high mate density, separated males obtained a partner earlier than females, who do not change movement with density.
Our data‐based simulations confirmed that the observed behavioural change by males contributes to enhancing encounters. Males at very low mate densities did best to move slowly and thereby reduce the risk of missing their stray partner, who is the only available mate. On the other hand, males that experienced high mate densities did better in mating encounters by moving fast because the risk of isolation is low, and they must compete with other males to find a partner.
These results demonstrate that termite males adaptively update their search strategy depending on conditions. Understanding the encounter dynamics experienced by animals is key to connecting the empirical work to the idealized search processes of theoretical studies.
This study reveals that termite males adjust their search mode to the density of potential mates. When a pair is separated at low densities, males move slowly to reduce the risk of missing their stray partner. At higher density, in contrast, males move fast because other mates are also available.
Inferring collective behaviour from a fossilized fish shoal Mizumoto, Nobuaki; Miyata, Shinya; Pratt, Stephen C
Proceedings - Royal Society. Biological sciences/Proceedings - Royal Society. Biological Sciences,
05/2019, Letnik:
286, Številka:
1903
Journal Article
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Collective motion by animal groups can emerge from simple rules that govern each individual's interactions with its neighbours. Studies of extant species have shown how such rules yield coordinated ...group behaviour, but little is known of their evolutionary origins or whether extinct group-living organisms used similar rules. Here, we report evidence consistent with coordinated collective motion in a fossilized group of the extinct fish Erismatopterus levatus, and we infer possible behavioural rules that underlie it. We found traces of two rules for social interaction similar to those used by extant fishes: repulsion from close individuals and attraction towards neighbours at a distance. Moreover, the fossilized fish showed group-level structures in the form of oblong shape and high polarization, both of which we successfully reproduced in simulations incorporating the inferred behavioural rules. Although it remains unclear how the fish shoal's structure was preserved in the fossil, these findings suggest that fishes have been forming shoals by combining sets of simple behavioural rules since at least the Eocene. Our study highlights the possibility of exploring the social communication of extinct animals, which has been thought to leave no fossil record.
In collective animal motion, coordination is often achieved by feedback between leaders and followers. For stable coordination, a leader's signals and a follower's responses are hypothesized to be ...attuned to each other. However, their roles are difficult to disentangle in species with highly coordinated movements, hiding potential diversity of behavioural mechanisms for collective behaviour. Here, we show that two
termite species achieve a similar level of coordination via distinct sets of complementary leader-follower interactions. Even though
females produce less pheromone than
, tandem runs of both species were stable. Heterospecific pairs with
males were also stable, but not those with
males. We attributed this to the males' adaptation to the conspecific females;
males have a unique capacity to follow females with small amounts of pheromone, while
males reject
females as unsuitable but are competitive over females with large amounts of pheromone. An information-theoretic analysis supported this conclusion by detecting information flow from female to male only in stable tandems. Our study highlights cryptic interspecific variation in movement coordination, a source of novelty for the evolution of social interactions.
The decentralized cognition of animal groups is both a challenging biological problem and a potential basis for bioinspired design. In this study, we investigated the house-hunting algorithm used by ...emigrating colonies of
ants to reach consensus on a new nest. We developed a tractable model that encodes accurate individual behavior rules, and estimated our parameter values by matching simulated behaviors with observed ones on both the individual and group levels. We then used our model to explore a potential, but yet untested, component of the ants' decision algorithm. Specifically, we examined the hypothesis that incorporating site population (the number of adult ants at each potential nest site) into individual perceptions of nest quality can improve emigration performance. Our results showed that attending to site population accelerates emigration and reduces the incidence of split decisions. This result suggests the value of testing empirically whether nest site scouts use site population in this way, in addition to the well-demonstrated quorum rule. We also used our model to make other predictions with varying degrees of empirical support, including the high cognitive capacity of colonies and their rational time investment during decision-making. In addition, we provide a versatile and easy-to-use Python simulator that can be used to explore other hypotheses or make testable predictions. It is our hope that the insights and the modeling tools can inspire further research from both the biology and computer science community.
Quorum responses and consensus decision making Sumpter, David J.T; Pratt, Stephen C
Philosophical transactions - Royal Society. Biological sciences,
03/2009, Letnik:
364, Številka:
1518
Journal Article
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Animal groups are said to make consensus decisions when group members come to agree on the same option. Consensus decisions are taxonomically widespread and potentially offer three key benefits: ...maintenance of group cohesion, enhancement of decision accuracy compared with lone individuals and improvement in decision speed. In the absence of centralized control, arriving at a consensus depends on local interactions in which each individual's likelihood of choosing an option increases with the number of others already committed to that option. The resulting positive feedback can effectively direct most or all group members to the best available choice. In this paper, we examine the functional form of the individual response to others' behaviour that lies at the heart of this process. We review recent theoretical and empirical work on consensus decisions, and we develop a simple mathematical model to show the central importance to speedy and accurate decisions of quorum responses, in which an animal's probability of exhibiting a behaviour is a sharply nonlinear function of the number of other individuals already performing this behaviour. We argue that systems relying on such quorum rules can achieve cohesive choice of the best option while also permitting adaptive tuning of the trade-off between decision speed and accuracy.
The study of rational choice in humans and other animals typically focuses on decision outcomes, but rationality also applies to decision latencies, especially when time is scarce and valuable. For ...example, the smaller the difference in quality between two options, the faster a rational actor should decide between them. This is because the consequences of choosing the inferior option are less severe if the options are similar. Experiments have shown, however, that humans irrationally spend more time choosing between similar options. In this study, we assessed the rationality of time investment during nest-site choice by the rock ant,
. Previous studies have shown that collective decision-making allows ant colonies to avoid certain irrational errors. Here we show that the same is true for time investment. Individual ants, like humans, irrationally took more time to complete an emigration when choosing between two similar nests than when choosing between two less similar nests. Whole colonies, by contrast, rationally made faster decisions when the options were more similar. We discuss the underlying mechanisms of decision-making in individuals and colonies and how they lead to irrational and rational time investment, respectively.
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