Creese R G, Underwood A J
School of Biological Sciences, University of Sydney, Zoology Building, 2006, Sydney, N.S.W., Australia.
Oecologia. 1982 Jun;53(3):337-346. doi: 10.1007/BF00389010.
The prosobranch limpet Cellana tramoserica grazes on microalgae, including the spores of macroalgae, and coexists with the pulmonate limpets Siphonaria denticulata and S. virgulata at mid-tidal levels on sandstone shores in New South Wales. These siphonarians graze on macroalgae, leaving the basal parts of the thalli intact. Where Cellana graze, they are capable of removing all algae; where Siphonaria graze, they leave at least a thin film of alga on the rocks, which is available to Cellana. S. denticulata normally show invariant homing behaviour, whereas S. virgulata tend to move around at random when Cellana are present, but apparently home when Cellana are absent. Both siphonarians have been observed to show opportunistic behavioural responses by moving towards patches of macroalgal foods when they become available.Experimental ecclosures of limpets at different densities and in different combinations revealed that Cellana tramoserica suffered increased mortality and reduced growth due to intraspecific competition when at increased densities. There was no effect on Cellana of increased densities of either species of Siphonaria. Nor was there any interspecific interaction between the siphonarians. Both species of Siphonaria showed some reduction of growth at increased intraspecific density. More importantly, both showed increased mortality when enclosed with low densities of Cellana. Larger densities of Cellana had no effect; the numbers of Cellana could not be maintained because of the reductions caused by intraspecific competition. Even after 27 weeks in enclosures with Cellana, the numbers of Siphonaria never declined to zero in any experimental enclosure. Thus, Cellana has a competitive effect on the survival of siphonarian limpets, but is unable to exclude them from an area of the shore. Siphonaria spp., in contrast, have no effect on Cellana.The nature of the competitive interactions between these types of limpets is explaied in terms of their methods of feeding; Cellana can exploit the food-resource before it reaches a suitable size for Siphonaria. The coexistence of Siphonaria spp. with Cellana is discussed with respect to the behaviour of the pulmonates. Intraspecific competition leading to reduced densitities of Cellana, however, will ensure that Cellana cannot exploit all the food resources, and some will be available to Siphonaria. The consequences of inter- and intra-specific competition among grazing gastropods are discussed with reference to the structure of intertidal communities, and it appears that competition for food is fundamentally different from competitive interactions for space in the organization of such communities.
原始腹足目帽贝细纹 Cellana tramoserica 以微藻为食，包括大型藻类的孢子，并与肺螺亚纲帽贝齿缘管唇螺 Siphonaria denticulata 和条纹管唇螺 S. virgulata 在新南威尔士州砂岩海岸的中潮位共存。这些管唇螺以大型藻类为食，使藻体基部保持完整。在 Cellana 觅食的地方，它们能够清除所有藻类；在管唇螺觅食的地方，它们会在岩石上至少留下一层薄薄的藻类，可供 Cellana 食用。齿缘管唇螺通常表现出不变的归巢行为，而条纹管唇螺在有 Cellana 存在时往往随机移动，但在 Cellana 不存在时显然会归巢。观察到这两种管唇螺在有大型藻类食物斑块出现时会表现出机会主义行为反应，朝着这些斑块移动。
对不同密度和不同组合的帽贝进行实验性围隔发现，细纹 Cellana tramoserica 在密度增加时，由于种内竞争，死亡率增加，生长受到抑制。管唇螺任何一种密度的增加对 Cellana 都没有影响。管唇螺之间也没有种间相互作用。两种管唇螺在种内密度增加时生长都有一定程度的降低。更重要的是，当与低密度的 Cellana 一起被围隔时，它们的死亡率都增加了。Cellana 密度更大时没有影响；由于种内竞争导致数量减少，Cellana 的数量无法维持。即使在与 Cellana 一起围隔 27 周后，在任何实验围隔中管唇螺的数量都从未降至零。因此，Cellana 对管唇螺帽贝的生存有竞争作用，但无法将它们从海岸的一个区域排除。相比之下，管唇螺对 Cellana 没有影响。
这些类型的帽贝之间竞争相互作用的性质可以根据它们的摄食方式来解释；Cellana 能够在食物资源达到管唇螺适宜大小之前就加以利用。管唇螺与 Cellana 的共存是根据肺螺亚纲动物的行为来讨论的。然而，导致 Cellana 密度降低的种内竞争将确保 Cellana 无法利用所有食物资源，一些资源将可供管唇螺利用。参照潮间带群落的结构讨论了植食性腹足类动物种间和种内竞争的后果，在这类群落的组织中，对食物的竞争似乎与对空间的竞争相互作用有着根本的不同。
