Spatial organization and interactions of harvester ants during foraging activity

Abstract

Local interactions, when individuals meet, can regulate collective behavior. In a system without any central control, the rate of interaction may depend simply on how the individuals move around. But interactions could in turn influence movement; individuals might seek out interactions, or their movement in response to interaction could influence further interaction rates. We develop a general framework to address these questions, using collision theory to establish a baseline expected rate of interaction based on proximity. We test the models using data from harvester ant colonies. A colony uses feedback from interactions inside the nest to regulate foraging activity. Potential foragers leave the nest in response to interactions with returning foragers with food. The time series of interactions and local density of ants show how density hotspots lead to interactions that are clustered in time. A correlated random walk null model describes the mixing of potential and returning foragers. A model from collision theory relates walking speed and spatial proximity with the probability of interaction. The results demonstrate that although ants do not mix homogeneously, trends in interaction patterns can be explained simply by the walking speed and local density of surrounding ants.

Spatial fidelity of workers predicts collective response to disturbance in a social insect

“…Despite growing interest in spatial dynamics within social insect colonies 21 , 45 , 55 , 65 , the importance of spatial fidelity for flexible task reallocation is not well understood. Our results provide evidence for three key tenets supporting a functional role of spatial fidelity in flexible task allocation in bumble bees: (a) the existence of spatial fidelity among workers (Fig.…”

“…While some models explicitly address spatial fidelity within nests, these have most often treated spatial distributions as a consequence of age-based movements within the nest 50 – 52 , mobility patterns 53 , or aggression 54 . Despite growing interest in the spatial organization of work (and workers) in social insect colonies 46 , 48 , 55 , the role of worker spatial fidelity in structuring access to local information sources within the colony and the importance of this aspect of worker spatial structure for task allocation is not well understood.…”

Ant colonies maintain social homeostasis in the face of decreased density

“…This implies that the form and function of an interaction rate may affect how its rate is affected by changes in the density of the society. Alternatively, or in addition to this, ants may be able to regulate their interaction rates actively to keep them at an optimal level for the colony by: (a) changing their movement and distribution in the nest (Adler and Gordon, 1992; Gordon et al, 1993; Davidson and Gordon, 2017), thus maintaining local density, or (b) making a change in their interaction behavior that is independent of local (realized) density. To examine the relative support for these two scenarios in our experimental data, we measured the local (realized) density around each ant, here defined as the mean number of other ants within 15 mm (please see 'Materials and methods' for details).…”

Multiple nest entrances alter foraging and information transfer in ants

“…Another important positive feedback known to regulate collective foraging activity in ants is the interaction rate between successful foragers and potential recruits that are present inside the nest [14][15][16][17]. In this case, the ant nest plays a key role in shaping interactions between these informed and naive colony members.…”