Dr Elva Robinson and colleagues in the University's School of Biological Sciences fitted rock ants with tiny radio-frequency identification tags [see image], each measuring 1 / 2,000 (one two-thousandth) the size of a postage stamp, then observed as they chose between a poor nest nearby and a good nest further away. The ant colonies showed sophisticated nest-site choice, selecting the superior site even though it was nine times further away than the alternative. The best nest was chosen, despite the fact that very few individual ants made direct comparisons between the nest-sites. . . .
Dr Robinson said: "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 behaviour substitutes for direct comparison, facilitating effective choice between nest sites for the colony as a whole."
Wednesday, April 22, 2009
How house-hunting ants choose the best home: