Mechanism of coexistence and competition in a three species coexisting system: case study for hermit crabs

对栖息于千叶潮间带岩岸的三种寄居蟹（Pagurus lanuginosus， P.filholi, Clibanarius virescens）的种间竞争进行了研究。这些物种的生境高度重叠，但存在较弱的地带性格局：filholi主要分布在潮间带的中部，绿草c分布在较低的位置，绿草p分布在最低的位置。对壳的利用模式有一定的重叠，均利用了绿口藻、唇形藻和月牙藻的壳。在实验室中观察到侵略性相互作用。两个物种中的一个个体被放在一个小水族箱里，一个个体的壳被人工打破，以提高攻击性，另一个处于自然状态。竞争激烈的上级通过直接的炮弹战从下级手中获得炮弹。攻击者最初把防御者的壳翻过来，然后用它的活动腿抓住它。这时，防守者完全缩进了壳里。在这种姿态下，由于壳孔对着对方，攻击者将它的鳍足插入防御者壳的孔中。然后攻击者直接开始攻击，并得到了防守者的壳。80个重复中，破碎壳中的绿芽孢杆菌感染filholi假单胞菌12例（15%）。在72个重复中，有2个（3%）得到了绿芽孢杆菌的壳。132个重复中，破碎壳中有20例filholi感染了P. lanuginosus（15%）。带破碎壳的P. lanuginosus从P. filholi获得壳；145个重复中97个（67%）。竞争等级为（最强优先）：P. lanuginosus>C.；virescens > P。filholi。这一顺序与潮间带从下到上的生境顺序一致，表明竞争优势种占据了更舒适的区域。

Interspecific competition was investigated in three species of hermit crabs Pagurus lanuginosus, P.filholi, Clibanarius virescens, in which they are inhabiting intertidal rocky shores in Chiba. Habitats of these species were highly overlapped, but weak zonation patterns were recognized : P. filholi mainly inhabited the middle intertidal zone, with C. virescens occupying a lower and P. lanuginosus lowest zones. Shell utilization patterns were overlapped, all of these species using shells of Chlorostoma lischkei, Monodonta labio, Lunella coronata coreensis. Aggressive interaction was observed in laboratory. One individual from two species were put in a small aquaria and one individual was provided with a shell that aperture was artificially broken to promote aggressiveness and another was in natural state. The competitive superiors obtained shell from the inferiors by direct shell fighting. The attacker initially turned over the shell of the defender and then hold it with its ambulatory legs. At this moment, the defender completely withdrew into the shell. In this attitude, with shell apertures facing each other, the attacker inserted its chelipeds into the aperture hole of the defender's shell. The attacker then proceeded directly into rapping and get the defender's shell. C. virescens in broken shells got shells from P. filholi in 12 cases among 80 replicates(15%). P. lanuginosus with broken shells got shells from C. virescens in 2 among 72 replicates(3%). P. filholi in broken shells got shells from P. lanuginosus in 20 cases among 132 replicates (15%). P. lanuginosus with broken shells got shells from P. filholi :. 97 among 145 replicates(67%). Competitive hierarchy is (strongest first) : P. lanuginosus>C. virescens>P. filholi. This order coincidents with the order of habitat from lower to upper intertidal zones, suggesting the competitive dominant species occupies more comfortable areas.