As the article "Do ants make direct comparisons?" explains, Temnothorax albipennis makes a collective decision when a colony emigrates to a new nest. Scouting ants that discover new nests assess them on the basis of multiple attributes. Some of these scouts subsequently recruit nest-mates to the new nest using tandem-running, where an informed ant leads a second ant to her destination. When the number of ants in the new nest reaches a quorum, scouts begin rapid transport of the rest of the colony by carrying nest-mates and brood. Colonies are able to choose the best of several nests. Two individual-level mechanisms for this collective choosiness have been identified. Some ants visit both nest sites, and subsequently recruit only to the better site, which has been taken as evidence for direct comparison. However, ants that visit only one site still contribute to the colony decision, by starting to recruit earlier (i.e. using a shorter recruitment latency) when a nest is of higher quality.
According to Elva Robinson, "Each ant appears to have its own 'threshold of acceptability' against which to judge a nest individually. Ants finding the poor nest were likely to switch and find the good nest, whereas ants finding the good nest were more likely to stay committed to that nest. When ants switched quickly between the two nests, colonies ended up in the good nest. Individual ants did not need to comparatively evaluate both nests in order for the entire colony to make the correct decision.
On the other hand, animals – including humans – who use comparative evaluation frequently make 'irrational' decisions, due to the context in which options are compared or by inconsistently ranking pairs of options, (for example option A preferred to B, B preferred to C but C preferred to A).
The ants' threshold rule makes an absolute assessment of nest quality that is not subject to these risks, and circumvents the necessity for memorization and comparison of every site visited. Thus, simple individual behavior substitutes for direct comparison, facilitating effective choice between nest sites for the colony as a whole."
Specimen: CASENT0173192Species: Temnothorax albipennis
Photographer: April NobileDate Uploaded: 08/09/2007
Copyright: California Academy of Sciences, 2000-2007
Specimen: CASENT0173192Species: Temnothorax albipennis
Photographer: April NobileDate Uploaded: 08/09/2007
Robinson, E., Smith, F., Sullivan, K., & Franks, N. (2009). Do ants make direct comparisons? Proceedings of the Royal Society B: Biological Sciences DOI: 10.1098/rspb.2009.0350
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