Beyond Migration: Causes and Consequences of Nomadic Animal Movements

Recent advances in animal tracking reveal that many species display irregular movements that do not fall into classical categories of movement patterns such as range residency or migration. Here, we develop a unifying framework that distinguishes these nomadic movements based on their patterns, drivers, and mechanisms. Though they occur in diverse taxa and geographic regions, nomadic movements are united by both their underlying environmental drivers, mainly environmental stochasticity, and the resulting irregular, far-ranging movement patterns. The framework further classifies types of nomadic movements, including full, seasonal, phase, irruptive, and partial nomadism. Nomadic movements can have unique effects on populations, communities, and ecosystems, most notably providing intermittent disturbances and novel introductions of propagules. Many animals move long distances in an irregular manner, and thus do not fit into the conventional categories of either seasonal migration or range residency. These nomadic movements can be distinguished from other forms of movement both qualitatively and quantitatively. Nomadism usually occurs in highly variable, resource-limited environments. It can also provide escape from natural disasters, predators, and parasites. Nomadic movements have unique impacts on animal populations, community ecology, and ecosystems. These impacts include increasing population sizes, promoting dispersal of propagules to novel environments, and stabilizing ecosystems.