Abstract
Hermit crabs are anomuran decapod crustaceans which have evolved the behabiour of utilizing empty gastropod shells as portable shelters. This paper briefly reviewed various aspects of population ecology of the hermit crabs. Hermit crabs in the field are generally unable to procure empty shells from living snails. Rather they are dependent ultimately upon snail mortality for shells. Snail size affects some parameters of the population through the individual-level processes of the crabs. Some studies indicate that crab growth is slowed by occupation of too small or too large shells. Fecundity is also affected directly by shell occupancy. Reduced clutch size is correlated with reduced shell size, even after the effects of crab size are taken in account. The flexibility in life history traits which shells regulated trade-off between growth and reproduction was reported. Crabs with large shells put effort to growth, while crabs in shells too small to permit growth allocate more time and energy into reproduction. There are considerable inferential and some direct evidences that hermit crab population are limited by supplies of empty shells. Adding many empty shells to the crab population in the field resulted in increasing the crab density. Finally, some problems of life history tactics of hermit crabs and other marine invertebrates are discussed.
