The ability to move in complex environments is, together with basic birth and death rates, one of the main factors affecting fitness and success of biological organisms. In some cases mobility is self-generated, and individuals perform some type of random or directed walk. In others, organisms are more or less passively transported by environmental flows, as in the case of plankton advected by marine currents.
In this talk I will visit a few ecological situations spanning a wide range of biological scales in which mobility plays a determinant role. A first theoretical approach explores the interplay between competition for resources, pattern formation, and type of motion (Brownian random walk vs Lévy flights) in an individual-based model of simple interacting organisms, showing that the type of motion can decide competition outcome. Then, more realistic studies of plankton abundance correlated with ocean turbulence will be described, to finally show that hydrodynamic structures may provide 'biological corridors' for marine birds.