Role of density in ant self-organized aggregation

Self-organized aggregation is a pervasive and important collective behavior, commonly found in biological species and in human society. It is a multi-disciplinary field widely studied in recent years. To study quantitatively macro-characteristics in self-organized aggregation, we performed experiments with ants (Tet-ramorium Caespitum )in a homogeneous environment to investigate relationship between self-organized aggregation and ant density. Aggregation intensity of ant groups was measured by hierarchic social entropy and quadrat method. Accurately controlled experiments and statistical analysis showed that ant groups had a close to random spatial distribution at low density, but a prominent state of aggregation emerged at high density. Therefore ant aggregation is density-dependent. Such data will be important regarding the micro-mechanism of ant self-organized aggregation. It is concluded that aggregation emergence is linked closely to density.