Italian freshwater decapods: exclusion between the crayfish Austropotamobius pallipes (Faxon) and the river crab Potamon fluviatile (Herbst).

In Italian freshwater systems, the crayfish Austropotamobius pallipes and the crab Potamon fluviatile mainly occur in different geographic areas and, when they are in sympatry, in different streams. Four issues are raised : (1) the two species once coexisted, (2) the two species share the same resources, (3) river crab is behaviorally dominant over crayfish, and (4) crab influences the habitat occupied by crayfish. These issues suggest a scenario of competitive exclusion in these two species, which is the result of past interspecific competition for common resources. The winner was P. fluviatile which had higher levels of aggression and strength than A. pallipes ; the latter was forced to migrate to other regions or, when still in sympatry, to remain in less favorable habitats, characterized by a lower temperature regime.