With this set-up lit 24 hours a day, ants’ digging activity was strongly stimulated and workers dug 2D tunnel networks in the sand within three days (fig. To prevent ants from escaping, an arena (diameter 50 cm) with a wall coated with Fluon GP2s was placed around the disk.
The mould was then removed and the disk of sand covered by a glass plate (25 cm 6 25 cm). We used fine yellow homogeneous sand which was poured into a mould and humidified by spraying with water (25 ml). The general experimental set-up consisted of a disk of sand (radius r ~ 100 mm, height h ~ 5 mm). We recorded and quantified the digging activity of groups of Messor sancta ants in a two dimensional and uniform environment. Let us briefly recall the main features of the experiments described in. Our experiments complied with the laws and ethical recommendations currently in effect in France where the experiments were performed. Messor sancta is not a protected nor endangered species. Colonies of ants Messor sancta were collected in southwestern France (Narbonne), on a private property with the permission of the owner. We conclude that an increase of the number of workers is a sufficient condition to induce a transition from tree-like to highly branched and meshed structures. In these conditions, the model predicts that the meshedness rapidly increases with the number of workers and then reaches a plateau at a critical size.
We then explore the predictions of the model over a large range of colony sizes in which collective digging progresses outward from a centre. We test the predictive power of the model for the networks meshedness with 50, 100 and 200 ants respectively. Here to investigate the impact of this parameter on the resulting network structure, we use the dataset obtained with the three group sizes and we introduce a new model that incorporates explicitly the ants digging activity level. However, preliminary numerical explorations showed that the number of workers might be worth further investigation. We then suggested that a next step should be a sensitivity analysis of the network topology to the model parameters. In a subsequent paper, we analyzed the tunneling dynamics using the dataset obtained with 200 workers and formulated a model for the network growth in which the tunnels were the basic units, focusing on their birth, growth and the intersection events between tunnels. We previously characterized the topological structure of the networks built by three group sizes (50, 100 and 200 workers). Hence we investigated the dynamics of collective digging in controlled laboratory conditions, allowing groups of ants to dig into horizontal moistened and homogeneous disks made of sand. However these methods cannot be used to follow the development of the nest structure over time. Structural features of a hypogeous nest can be quantified with plaster or aluminium casts at a given moment of colony life. Quantitative descriptions of nests dug in natural conditions are difficult to obtain. As a general trend, however, nest complexity increases with colony size (see Table 1). In most ant genera, nests are subterranean excavated networks, but within each particular genus, there exists a large variability of nest size and complexity. So far no correlation has been established between the observed variations in the complexity of nest architecture and phylogeny. The simplest nests are made up of a few chambers stacked along a single vertical tunnel, whereas dense networks of tunnels with a large number of interconnected chambers are found in the most complex nests. In addition to the adjustment of nest volume, the variations of ant nest architecture with colony size result in a different number of chambers and tunnels. Previous field studies and controlled laboratory experiments have shown that nest size was proportional to the size of a colony in several species of ants. The tunnels ensure the connection of the underground parts of the nest to the soil surface.
Sometimes they may also be used as resting places in which dense aggregations of workers can be found.
These chambers are ellipsoidal cavities used to raise brood, store seeds, grow fungus or accumulate litter and corpses. species of ants excavate their nest and form a subterranean network of tunnels that connect several chambers.
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