Is Large Body Size always Advantageous for Terrestrial Adaptation?

摘要: Sesarmops intermedium de Haan (1835) is a semi-terrestrial crab inhabiting the areas around forest creek at Heng-chun Peninsula in southern Taiwan. Small and large individuals excavate tunnels near waterline, while those with medium body size are more distant from water. This unusual distribution pattern might reflect habitat preference related to physiological requirement of crabs different sizes. In natural conditions, animals keep their haemolymph osmolality relatively low level fully-rehydrated individuals. dehydrated animal was much higher negatively size. Both rates water loss uptake decrease increasing While, both potential time exposed air rehydration increase The rate may prolong air, but this advantage be offset by efficiency simultaneously. crabs, high small amount requirement, have shorter needed for rehydration. However, smaller than about 2 g living weight, due extremely fast water, access frequently thus lower terrestrial activity also. For sized advantages rate, less better ability utilize interstitial allow them emancipate body. Due constraints performance balance, optimum extending S. below 14 weight (=28.5 mm carapace width) which activity. adaptation regarding balance intermedium, how capability use various on land seem important reduce rate. Large hence not always advantageous possibly other crustaceans.