Accurate decisions in an uncertain world: collective cognition increases true positives while decreasing false positives
Wolf, M. ; Kurvers, R.H.J.M. ; Ward, A.J.W. ; Krause, S. ; Krause, J. - \ 2013
Proceedings of the Royal Society. B: Biological Sciences 280 (2013)1756. - ISSN 0962-8452 - 9 p.
antipredator vigilance - social information - predatory attack - fish shoals - flocking - evolution - selection - flight - birds - foragers
In a wide range of contexts, including predator avoidance, medical decision-making and security screening, decision accuracy is fundamentally constrained by the trade-off between true and false positives. Increased true positives are possible only at the cost of increased false positives; conversely, decreased false positives are associated with decreased true positives. We use an integrated theoretical and experimental approach to show that a group of decision-makers can overcome this basic limitation. Using a mathematical model, we show that a simple quorum decision rule enables individuals in groups to simultaneously increase true positives and decrease false positives. The results from a predator-detection experiment that we performed with humans are in line with these predictions: (i) after observing the choices of the other group members, individuals both increase true positives and decrease false positives, (ii) this effect gets stronger as group size increases, (iii) individuals use a quorum threshold set between the average true- and false- positive rates of the other group members, and (iv) individuals adjust their quorum adaptively to the performance of the group. Our results have broad implications for our understanding of the ecology and evolution of group-living animals and lend themselves for applications in the human domain such as the design of improved screening methods in medical, forensic, security and business applications.
The influence of social interactions on the foraging path of Bewick's Swans Cygnus columbianus bewickii
Klaassen, R.H.G. ; Nolet, B.A. ; Bankert, D. - \ 2006
Ardea 94 (2006)3. - ISSN 0373-2266 - p. 477 - 484.
tundra swans - behavior - information - habitat - efficiency - migration - depletion - foragers - patterns - tubers
The efficiency in which high-density food patches are found is determined by the way foragers move between patches. In this study we explore the effect of social interactions on the foraging path, in particular the distance moved between patches. We studied Bewick¿s Swans Cygnus columbianus bewickii that foraged on belowground tubers of Fennel Pondweed Potamogeton pectinatus. We accurately mapped the foraging path of individual swans and determined the distances between visited patches. 24% of inter-patch movements are associated with social interactions. When a swan retreats from a patch because it is chased away by another swan, it moves a significantly larger distance to a patch than if the movement is not associated with a social interaction. Such longer movements are thought to reduce the rate at which high-density patches are encountered, and thus the energy gain rate a swan can achieve. We observed a strong social hierarchy in which families are dominant over pairs and singletons, and pairs are dominant over singletons, which represents a producer¿scrounger model. Singletons were most frequently observed to retreat from patches and are consequently thought to achieve the lowest gain rates, and also as a result exhibit the slowest speed of movement between patches. However singletons might partly compensate for more frequent retreats from patches by moving larger distances to arrive at the front edge of a flock where they encounter unexploited resources.