コメツキガニの行動と相互作用

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We have investigated the coaction between individuals of the sand-crab, Scopimera globosa DE HAAN, observing their behavior and the distribution of nest-holes, on the shore of the inner part of Tanabe Bay during July, 1953 and 1954,and the following results were obtained. 1) This crab lives in the sandy flat between the lines of the lower high tide and the higher low tide. 2) Tidal rhythmicity seems to be most prominent in the activities of this crab. Diel activity is of less importance. 3) There were observed two kinds of fighting between individuals : one is the sudden attacking without apparent reason and the other is in defence of the nest-hole when other crabs approach it. 4) The home-ranges coincide with the feeding areas, which do not overlap each other. They feed on fragments of small animals and sea-weeds, and plankton organisms attached to fine sand grains. They devour them together with the sand and the sand grains are disgorged forming "sand-pellets". Three types of the distribution of the sand-pellets are distinguished according to the variation of the population density of the sandcrabs. In the case of low density, the sand-pellets show uniform distribution except towards other nest-holes. In the case of fairly high density, the sand-pellets distribute in the shape of narrow sectors radiating from the nest-holes. In the case of very high density, which is not found under natural conditions but is made only experimentally, fighting happens frequently, the feeding area is overlapped, and the sand-pellets show a very irregular distribution making two or three layers on the ground. Another type of distribution of the sand-pellets is observed when they are made during night. 5) During the ebb tide, some crabs exchange their nest-holes and some of others make new ones. If the deserted nest-holes are not occupied again, they are destroyed by the rising tide. With these processes the distribution or nest-holes seems to tend to become uniform. In the field experiments, in which the population density is made about three times higher than the original density, some crabs are driven away to reduce the population to its original number. On the contrary, if the area is cleared off, new crabs invade the area and the population reaches the original number. 6) Statistically, the distribution of nest-holes is different according to the population density. In the case of low density, in spite of the fact that the distribution of the nest-holes is near-random, the coaction between individuals is clearly observed in fightings and nest-hole changes. In the case of fairly high density, the distribution is far from random, conforming to the mode of negatively contagious, and, of course, the coaction above mentioned is clearly observed. These observations teach us that the mere application of a statistical method on the distribution of the nest-holes does not necessarily clarify the existence of coaction between individuals. 7) All of the coactions mentioned above seem to be caused mainly with relation to their feeding behavior.
日本生態学会の論文
1955-03-31

コメツキガニの行動と相互作用

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