Abstract
Abstract. Social insect colonies possess remarkable
abilities to select the best among several courses of action. In populous
societies with highly efficient recruitment behaviour, decision-making is
distributed across many individuals, each acting on limited local
information with appropriate decision rules. To investigate the degree
to which small societies with less efficient recruitment can also
employ distributed decision-making, we studied nest site selection in
Leptothorax albipennis. Colonies were found to make sophisticated
choices, taking into account not only the intrinsic qualities of
each site, but also its value relative to the available options. In
choices between two sites, individual ants were able to visit both
sites, compare them and choose the better one. However, most ants
encountered only one site in the course of an emigration. These poorly
informed ants also contributed to the colony's decision, because
their probability of initiating recruitment to a site depended on
its quality. This led to shorter latencies between discovery and
recruitment to a superior site, and so created greater amplification via
positive feedback of the population at the better site. In short, these
small colonies make use of a distributed mechanism of information
processing, but also take advantage of direct decision-making by
well-informed individuals. The latter feature may in part stem from the
limitations of their social structure, but may also reflect the stringent
demand for unanimous decisions by house-hunting colonies of any size.
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