McClanahan Timothy R
Coral Reef Conservation Project, P.O. Box 99470, Mombasa, Kenya.
East African Centre, Friends World College, P.O. Box 526, Machakos, Kenya.
Oecologia. 1988 Nov;77(2):210-218. doi: 10.1007/BF00379188.
Coexistence between the coral reef inhabiting sea urchins Echinometra mathaei, Diadema savignyi and D. setosum was studied by comparing differences in body morphology, distribution, diet, susceptibility to predators, intra- and interspecific competition and settlement. The three species share similar diets and broad within-habitat distributions but differ in their microspatial preferences. E. mathaei is the smallest species, has the highest settlement rates and lives territorially within small burrows or crevices. D. savignyi is intermediate in size and lives frequently in intermediate size crevices or occassionally in social groups. D. setosum is the largest species and occassionally lives in large crevices or more frequently in social groups. Both Diadema have similarily low settlement rates. Competition experiments showed that E. mathaei was consistently the top competitor for crevice space. Diadema species shared larger crevices but competition occured within smaller crevices and was frequently won by the largest individual, regardless of species. D. savignyi may be the top competitor for crevice space between the Diadema species due to a reduced spine length/test size ratio which gives it a larger test for the same crevice size requirement. Predation rates were high for E. mathaei and low for both Diadema species. Coexistence is mediated by predation on the competitive-dominant while predation coupled with different body morphologies and behavior allows spatial resource partitioning of the reef's variable topography. Consequently, the three variables of predation, topographic complexity and differing body shapes create the observed species diversity. A reduction in predators due to stochastic fluctuations or from fishing pressure can lead to E. mathaei population increases and competitive exclusion of Diadema.
通过比较栖息在珊瑚礁中的海胆马氏长海胆（Echinometra mathaei）、刺冠海胆（Diadema savignyi）和刺冠长海胆（D. setosum）在身体形态、分布、饮食、对捕食者的易感性、种内和种间竞争以及定居方面的差异，对它们的共存情况进行了研究。这三个物种具有相似的饮食和广泛的栖息地内分布，但在微空间偏好上有所不同。马氏长海胆是最小的物种，定居率最高，在小洞穴或裂缝中以领地形式生活。刺冠海胆体型中等，经常生活在中等大小的裂缝中，偶尔也生活在社会群体中。刺冠长海胆是最大的物种，偶尔生活在大裂缝中，更频繁地生活在社会群体中。两种刺冠海胆的定居率都同样较低。竞争实验表明，马氏长海胆一直是裂缝空间的顶级竞争者。刺冠海胆物种共享较大的裂缝，但在较小的裂缝中会发生竞争，并且通常由最大的个体获胜，无论其物种如何。由于刺长/壳径比降低，在相同的裂缝大小需求下，刺冠海胆的壳更大，因此刺冠海胆可能是刺冠海胆物种之间裂缝空间的顶级竞争者。马氏长海胆的捕食率很高，而两种刺冠海胆的捕食率都很低。共存是通过对竞争优势种的捕食来调节的，而捕食与不同的身体形态和行为相结合，使得珊瑚礁多变地形的空间资源得以划分。因此，捕食、地形复杂性和不同的身体形状这三个变量造就了观察到的物种多样性。由于随机波动或捕捞压力导致的捕食者减少，可能会导致马氏长海胆种群增加，并对刺冠海胆产生竞争排斥。
