Aggregation dynamics of terrestrial isopods under extended Vicsek model

Abstract

Terrestrial isopods display a rich behavioral repertoire, including fast escape responses and aggregation dynamics. Their response to environmental stimuli such as artificial light, humidity, vibration, heat and predation stress has been documented, but research highlights a variability in these responses, depending on the studied species and the different ecological niches they inhabit. The Vicsek model is widely used in the study of collective behavior and has been adapted multiple times to model different biological phenomena. In this work, we exposed terrestrial isopod Porcellionides pruinosus to different combinations of vibration and light stimuli within a circular enclosure and used the resulting experimental observations to extend the Vicsek model to account for aggregation dynamics and speed variability. To this end, we modeled aggregation dynamics using local group size and edge proximity to modulate aggregation probability. Our experimental results suggest that the combined effect of light and vibration increases the speed of isopods more than light or vibration alone. Additionally, the speed relaxation also occurs later when exposed to the combined stimuli. Interestingly, the classic Vicsek model correctly predicted the motion of isopods only within a few seconds under stimuli presence, indicating the isopods move in a collective fashion at short time scales. In contrast, the results of simulating swarms with the extended Vicsek model were consistent with the mean square displacement of the experimentally tracked isopods over longer times and also, depending on the stimuli, for the short times. This extension of the Vicsek model provides a framework that can be used for multi-modal stimuli testing of terrestrial collective and aggregation invertebrate behavior, thus providing a platform to understand better the variability of the responses of these valuable members of the ecosystem.