Hermit crabs in a mangrove swamp: proximate and ultimate factors in the clustering of Clibanarius laevimanus.

The proximate and ultimate factors of the clustering behavior in the mangal-dwelling hermit Clibanarius laevimanus have been studied at Mida Creek, Kenya. First, field experiments showed that the hermits correctly oriented towards their clustering sites after deprivation of references from the sky, landscape, and substrate. Second, the pros and cons are weighed of various hypotheses on the adaptive significance of clustering; the most plausible is that aggregations may serve as ''shell exchange markets''. Although shell exchange is rare, most hermits in the group could benefit from such a chain process, and the adaptive significance of clustering could be ''magnified''.