Active behavior and 1/f noise in shell-changing behavior of the hermit crabs.

Hermit crabs are known to carry a gastropod shell to prevent abdomen from injuring by predators and cannibalism. One can regard the shell as a boundary between inside and outside worlds for hermit crabs. We conducted an experiment in which hermit crabs without shells deal with artificial tubes. The situation without a shell requires a part of experimental setup to be regarded as inside by each hermit crab. We accept the distance of locomotion as the indication of the estimation process performed by an individual on parts of the experimental setup. As a result, behavioral hierarchy was found with respect to the way of constituting the boundary. At each level of hierarchy, active behavior produced 1/f noise in comparison with the passive one. It suggests that finding 1/f noise at each level of hierarchy may lead to a lower level of hierarchy in another situation.