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

对生活在千叶潮间带岩岸的3种寄居蟹Paguruslanaguosus、P.filholi和Clibanariusvirescens的种间竞争进行了研究。这些种的群落高度重叠，但分带性较弱：P. filholi主要分布于中潮间带，C. virescens和P. lanadorosus最低。贝壳利用模式重叠，所有物种都使用Chlorostoma lischkei，Monodonta labio和Lunella coronata coreensis的贝壳。在实验室中观察到攻击性相互作用。将两个物种的一个个体放入小型水族箱中，一个个体被提供有人工打破孔径以促进攻击性的壳，另一个处于自然状态。竞争优势通过直接的炮弹战斗从邻近的敌人那里获得炮弹。攻击者最初把防御者的外壳翻过来，然后用它的走动腿抓住它。这一刻，防御者完全缩回了壳内。在这种姿态下，贝壳的孔彼此面对，攻击者将它的螯足插入防御者贝壳的孔中。然后攻击者直接进入说唱，并获得防御者的壳。C.在80个重复中，有12个（15%）被破壳的绿僵菌从菲霍氏棘球蚴上获得了壳。P. lananjuosus从C.在72份重复样品中，2份（3%）检出绿脓杆菌。在132个重复中，有20个（15%）从绒螯蟹身上获得了裂壳的菲氏原螯虾壳。裂壳的P. lanjuosus从P. filholi获得贝壳：。97/145份重复样品（67%）。竞争等级为（最强者为第一）：P. lananjuosus>C.绿毛蕨>黄毛蕨。这一顺序与栖息地从低到高的潮间带的顺序相一致，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.