Better not move randomly

Example of marine copepod swimming patterns. Four 1-minute trajectories in each panel: (a) Clausocalanus furcatus fast cruising pattern, (b) Temora stylifera female, (c) C. furcatus swim-and-sink pattern (sink in red), (d) T. stylifera male.

How organisms move through their environment determines how often they encounter prey, predators and mates. In a recently published paper on the Royal Society Interface (link) we outline a method – the trajectory self-overlap – that gives direct estimates of the resources and risks encountered by a moving animal. We applied this method to the three-dimensional world of plankton revealing fundamental compromise in how these organisms move.

There is a controversy surrounding the supposed prevalence of Lévy Walk (or Lévy Flight) in animal movement patterns. The case for Lévy Walks is almost universally posed in terms of search efficiency. However, movement patterns must also contend with predation risk. It appears from our analysis that the tortuosity of plankton motion has little to do with search efficiency, but is largely a response to predator avoidance. This is particularly apparent in swimming behaviours with long systematic correlations, such as for helical or loop-forming swimming patterns.

Avoiding moving in a random fashion and exploring their environment with regular trajectories, planktonic organisms can maintain high search efficiency for prey while keeping their exposure to predation risk at a minimum!

/Giuseppe