Ecology. 2014 Jan;95(1):185-96. doi: 10.1890/13-0496.1.
Facilitation cascades arise where primary foundation species facilitate secondary (dependent) foundation species, and collectively, they increase habitat complexity and quality to enhance biodiversity. Whether such phenomena occur in nonmarine systems and if secondary foundation species enhance food web structure (e.g., support novel feeding guilds) and ecosystem function (e.g., provide nursery for juveniles) remain unclear. Here we report on field experiments designed to test whether trees improve epiphyte survival and epiphytes secondarily increase the number and diversity of adult and juvenile invertebrates in a potential live oak-Tillandsia usneoides (Spanish moss) facilitation cascade. Our results reveal that trees reduce physical stress to facilitate Tillandsia, which, in turn, reduces desiccation and predation stress to facilitate invertebrates. In experimental removals, invertebrate total density, juvenile density, species richness and H' diversity were 16, 60, 1.7, and 1.5 times higher, and feeding guild richness and H' were 5 and 11 times greater in Tillandsia-colonized relative to Tillandsia-removal limb plots. Tillandsia enhanced communities similarly in a survey across the southeastern United States. These findings reveal that a facilitation cascade organizes this widespread terrestrial assemblage and expand the role of secondary foundation species as drivers of trophic structure and ecosystem function. We conceptualize the relationship between foundation species' structural attributes and associated species abundance and composition in a Foundation Species-Biodiversity (FSB) model. Importantly, the FSB predicts that, where secondary foundation species form expansive and functionally distinct structures that increase habitat availability and complexity within primary foundation species, they generate and maintain hot spots of biodiversity and trophic interactions.
促进级联现象是指初级基础物种促进次级（依赖）基础物种，它们共同增加栖息地的复杂性和质量，从而提高生物多样性。这种现象是否会在非海洋系统中发生，以及次级基础物种是否会增强食物网结构（例如，支持新的取食群体）和生态系统功能（例如，为幼体提供养育场所）尚不清楚。在这里，我们报告了一系列野外实验，旨在测试树木是否能提高附生植物的存活率，以及附生植物是否能在潜在的栎属- Tillandsia usneoides（西班牙苔藓）促进级联中，间接增加成年和幼年无脊椎动物的数量和多样性。我们的结果表明，树木减少了对 Tillandsia 的物理压力，从而促进了 Tillandsia 的生长，而 Tillandsia 的生长又减少了对无脊椎动物的干燥和捕食压力。在实验移除中，无脊椎动物总密度、幼体密度、物种丰富度和 H'多样性分别高出 16、60、1.7 和 1.5 倍，取食群体丰富度和 H'分别高出 5 和 11 倍。在整个美国东南部的调查中， Tillandsia 对群落的增强作用相似。这些发现表明，一个促进级联组织了这个广泛分布的陆地生物群，扩展了次级基础物种作为营养结构和生态系统功能驱动因素的作用。我们在一个基础物种-生物多样性（FSB）模型中，将基础物种的结构属性与其相关物种的丰度和组成联系起来。重要的是，FSB 预测，在次级基础物种形成广阔且功能独特的结构，增加初级基础物种内的栖息地可利用性和复杂性的情况下，它们会产生和维持生物多样性和营养相互作用的热点。
