Competitive dynamics of a Mediterranean hermit crab assemblage: the role of interference and exploitative competition for shells.

On a Mediterranean rocky shore, the shallow-water hermit crab assemblage is mostly composed of Clibanarius erythropus, exclusively inhabiting conventional gastropod shells, and Calcinus tubularis, which in part lives in fixed vermetid tubes. Laboratory experiments showed that shells are preferred by both species. If vermetid tubes are ‘the best of a bad situation’, the dominance expressed by Clibanarius over Calcinus does not result from an active competitive exclusion, as shown in laboratory experiments, but rather is the consequence of this species' greater ability to find and utilize vacant shells in the habitat.