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First published online July 25, 2005
Journal of Experimental Biology 208, 2903-2912 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01711

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Temporal organization of bi-directional traffic in the ant Lasius niger (L.)

Audrey Dussutour^1,*, Jean-Louis Deneubourg² and Vincent Fourcassié^1,

¹ Centre de Recherches sur la Cognition Animale, UMR CNRS 5169, Université Paul Sabatier, 118 route de Narbonne, F-31062, Toulouse Cedex 4, France
² Service d'Ecologie Sociale and Centre d'Etudes des Phénomènes Non-linéaires et des Systèmes Complexes, Université Libre de Bruxelles, CP231, Boulevard du Triomphe, B-1050 Bruxelles, Belgium

View larger version (12K): [in a new window]   Fig. 1. Schematic illustration of the 3 mm-width bridge, with the different sectors defined for the analysis of the ants' individual behaviour.

View larger version (16K): [in a new window]   Fig. 2. Mean number of ants per minute crossing the bridge in both directions every 3 min. Values are means ± S.E.M. N=15 trials for both bridge widths.

View larger version (22K): [in a new window]   Fig. 3. Effect of the number of encounters with contact on the duration of travel between the two bottlenecks of the bridge for the two bridge widths studied. The slope of the linear regression lines corresponds to the time lost by each ant per interaction; its intercept gives the duration of travel without interaction. N=133 and N=126 for the 3 mm and 10 mm bridge, respectively.

View larger version (26K): [in a new window]   Fig. 4. Relationship between the number of encounters with contact and the total number of encounters per ant for each bridge width studied. The slope of the lines corresponds to the probability of an ant travelling on the bridge to be contacted by another ant during an encounter. N=133 and N=126 for the 3 mm and 10 mm bridge, respectively.

View larger version (12K): [in a new window]   Fig. 5. Experimental results. Distribution frequency of the size of the groups of successive ants travelling in the same direction identified at the level of the line between the bottleneck and the entrance on the nest side of the bridge for each bridge width. The distribution frequency of group size obtained with a random sequence of ants generated on the basis of an equal probability of occurrence of nestbound and outbound ants is also represented. N=1203 and N=905 for the 10 mm and 3 mm bridge, respectively.

View larger version (16K): [in a new window]   Fig. 6. Distribution of the time spent crossing the bottlenecks and the entrances for ants travelling to and from the centre of a 3 mm bridge (for each sector, the results for the nest and source sides of the bridge have been pooled). The dotted lines within the boxplots represent the median, the lower and upper boundaries of the boxes represent, respectively, the 25th and 75th percentiles, while the whiskers extend to the smallest and largest values within 1.5 box lengths. The open circles represent the outliers. N=500 for each box plot.

View larger version (19K): [in a new window]   Fig. 7. Simulation results. Distribution frequency of the size of the groups of successive ants travelling in the same direction at the level of the line between the bottleneck and the entrance on the nest side of the bridge when the simulations were run with a flow of ants entering the bottlenecks of the bridge equal to 0.5 ants per time step, corresponding to the flow measured in the experiments on a 3 mm bridge. The simulations were run with and without implementing a cooperative rule between following ants. For explanations on the random distribution, see Fig. 5.

View larger version (21K): [in a new window]   Fig. 8. Simulation results. Distribution frequency of the size of groups of successive ants travelling in the same direction at the level of the line between the bottleneck and the entrance on the nest side of the bridge, when the simulations were run with increasing values of the flow of ants entering the bridge. For explanations on the random distribution, see Fig. 5. The inset shows the mean group size obtained for different values of entrance flow.