Nest shape influences colony organization in ants: spatial distribution and connectedness of colony members differs from that predicted by random movement and is affected by nest space

Abstract

Many social animals produce architectures that greatly increase the builder’s ability to survive across environments. For example, the many forms and functions of ant nests facilitate their ability to occupy nearly every biome. However, nest shape is not always just determined by the ants, as some species inhabit cavities with externally determined shapes, such as rock crevices or hollow sticks. In both cases, we can ask not only how ant behaviour can affect the form and function of nests, but also how nest shapes impact the inhabiting ant colony’s behaviour. We examined how the spatial organization of Temnothorax rugatulus ants differed across given artificial nests with radically different internal shapes. We used geometric measures to describe the emerging spatial relationships of workers, brood, queens, and alates in these two shapes, and show that overall distributions of all types of colony members are influenced by nest shape. However, we also found that individual spatial fidelity zone size, i.e. the areas repeatedly occupied by individuals, which may be linked to their division of labor, are overall not affected by nest shape. This is despite the fact that spatial fidelity zone size does vary as a function of distance from the nest entrance and the brood center; and that this relationship is affected by both nest shape and density. Finally, we show that workers are found closer to the entrance of the nest than would be expected in a random walk model in both nest shapes. These findings indicate that ants actively regulate which areas of a nest they occupy, and that they may compensate for effects of nest architecture constraints. We conclude in this study that physical properties of nests can influence the in-nest spatial organization of ant colonies, which highlights the need to explore nest shape as a direct influence on the organization, movement, and communication of the inhabiting ant colony.