The velocity and quiescence distributions in spontaneous locomotion across animals vary between modes of movement

Abstract

Abstract Locomotion in animals follows simple mathematical rules: when active, most time is spent at lower velocities and exponentially decreasing time is spent at increasing velocities; when inactive, there is an abundance of short quiescence periods decreasing by an inverse power function towards longer quiescence periods. We investigated whether these mathematical rules are ‘universal’, i.e. followed by all animals independently of their modes of movement (walking, gliding/crawling, swimming) or their habitat (land, water). Using automated video tracking with high temporal and spatial resolution, we investigated the velocity and quiescence period distributions in ten species representing major divisions of the animal kingdom (snails, woodlice, springtail, beetle, fish, reptile, chicken and mouse). We confirm that the two functions are followed by most species, although we also found important exceptions: the snails and woodlice showed uni- or bimodal velocity distributions; the snails did not follow the inverse power law of quiescence periods. Thus, most animals running on legs or swimming follow the expected distributions, while other runners (isopods) and substrate gliders/crawlers (snails) do not. We suggest a difference in velocity distribution between animals that use running to escape predators and those that do not (snails and woodlice).