Clustering experiments.

<p>Objects are uniformly distributed along the border of a 50 cm diameter circular arena. Ants enter the arena spontaneously from below, mounting along a wood stick through the hole in the arena center. Two different initial one-dimensional densities are used: 127 and 255 objects per meter. The duration of each experiment is 50 hours. Fig. A and Fig. B correspond respectively to the beginning and the end of a high density experiment. Fig. C and Fig. D display the time series of the number of piles (mean s.d.) for the low and the high density experiments, respectively. Piles are defined as follows: Two neighboring objects are considered to belong to the same cluster if the distance between them is less than 1 mm. A cluster constitutes a pile if it contains at least 6 objects. In <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0038588#pone.0038588-Theraulaz2" target="_blank">[41]</a> another circular arena with a 25 cm diameter was also used (with the same low and high initial densities). For the purpose of the methodological illustration in the first part of the results section only the large arena is used, but the model built in the second part of the results section is compatible with all observations, including the ones in small arenas (see Fig. 6).