Altieri Andrew H, Silliman Brian R, Bertness Mark D
Department of Ecology and Evolutionary Biology, Brown University, Providence, Rhode Island 02912, USA.
Am Nat. 2007 Feb;169(2):195-206. doi: 10.1086/510603. Epub 2007 Jan 2.
It has recently been proposed that many communities are structured by a hierarchy of interactions in which facilitation by foundation species is of primary importance. We conducted the first explicit experimental test of this hypothesis by investigating the organization of positive interactions on New England cobblestone beaches. In this midintertidal community, wave-generated substrate instability and solar stress largely limit marine organisms to the shelter of cordgrass beds. Cordgrass, which can establish and persist without the aid of other foundation species, facilitates a dense assemblage of inhabitants (e.g., mussels, snails, seaweeds) with roots/rhizomes that stabilize substrate and a dense canopy that baffles waves and provides shade. Within the cordgrass bed community, ribbed mussels further enhance physical conditions and densities of other species (e.g., amphipods, barnacles) by providing crevice space and hard substrate. We conclude that cordgrass bed communities are hierarchically organized: secondary interactions (e.g., facilitation by ribbed mussels) play a key role within an assemblage dependent on primary facilitation by the independently successful foundation species cordgrass. Our results identify emergent indirect positive interactions in the form of facilitation cascades, have broad implications for conservation, and help unify existing models of community organization that were developed without considering the fundamental role of positive interactions.
最近有人提出，许多群落是由一系列相互作用构成的层级结构，其中基础物种的促进作用至关重要。我们通过研究新英格兰鹅卵石海滩上的正向相互作用的组织方式，对这一假设进行了首次明确的实验检验。在这个潮间带中部群落中，海浪引起的底物不稳定性和太阳辐射压力在很大程度上限制了海洋生物只能栖息在互花米草床的庇护之下。互花米草无需其他基础物种的帮助就能扎根并存活，它促进了大量生物（如贻贝、蜗牛、海藻）的聚集，这些生物的根/根茎能稳定底物，茂密的树冠能阻挡海浪并提供遮荫。在互花米草床群落中，带肋贻贝通过提供缝隙空间和坚硬底物，进一步改善了其他物种（如双足虾、藤壶）的物理条件和密度。我们得出结论，互花米草床群落是层级组织的：次级相互作用（如带肋贻贝的促进作用）在依赖独立成功的基础物种互花米草的初级促进作用的组合中起着关键作用。我们的研究结果识别出了以促进级联形式出现的间接正向相互作用，对保护具有广泛的意义，并有助于统一在未考虑正向相互作用的基本作用的情况下发展起来的现有群落组织模型。
