Department of Biology, University of Texas at Arlington, 501 S. Nedderman Drive, Arlington, Texas, 76019, USA.
Washington State Department of Ecology, Environmental Assessment Program, 300 Desmond Drive SE, Lacey, Washington, 98503, USA.
Ecology. 2019 Nov;100(11):e02831. doi: 10.1002/ecy.2831. Epub 2019 Aug 27.
We developed a framework for the hierarchical pathways of bottom-up (niche dimensionality) and top-down control (herbivory) on biomass of stream algae via changes in guild composition (relative abundance of low profile, high profile, and motile guilds), species richness, and evenness. We further tested (1) the contrasting predictions of resource competition theory vs. the benthic model of coexistence on how the number of added nutrients constrains species richness, (2) the relationship between species richness and evenness, and (3) the biodiversity-ecosystem-function paradigm. Implementing a combination of field and lab experiments that manipulated for the first time in benthic algae herbivory and/or niche dimensionality, i.e., the number of added nutrients (NAN), including nitrogen, phosphorus, iron, and manganese, we made the following discoveries. First, important predictors of guild composition were herbivory (field) and NAN (lab); of richness, NAN (field) and NAN and guild composition (lab); of evenness, guild composition (field and lab) and herbivory (field); and of biomass, guild composition, NAN, and richness + evenness (field and lab). Herbivory increased the proportions of the low profile and motile guilds but decreased the proportion of the high profile guild. In the absence of grazing, greater proportions of the high profile guild resulted in elevated richness and biomass but diminished evenness, whereas in the presence of grazing, these relationships generally disappeared. Second, both experiments confirmed the prediction of the benthic model that species richness increases with NAN, a pattern inconsistent with resource competition theory. Third, supplementation with manganese and/or iron increased algal richness, indicating that micronutrients, which have generally been overlooked in stream ecology, added dimensions to the algal niche. Fourth, the richness-evenness relationship, observed only in the absence of herbivory, depended on the size of the species pool. It was positive at richness lower than 49 species (lab), implying complementarity and facilitation, while at higher richness (field and lab), this relationship was negative, consistent with negative interspecific interactions. Finally, the greater dependence of biomass production on guild composition and NAN than on richness and evenness suggests that more comprehensive, environmentally explicit, and trait-based approaches are necessary for the study of the biodiversity-ecosystem-function paradigm.
我们建立了一个框架，用于研究自下而上（生态位维度）和自上而下（食草作用）对溪流藻类生物量的控制途径，这些途径通过改变 guild 组成（低轮廓、高轮廓和运动型 guild 的相对丰度）、物种丰富度和均匀度来实现。我们进一步测试了以下内容：（1）资源竞争理论与底栖共存模型对添加养分数量如何限制物种丰富度的对比预测；（2）物种丰富度和均匀度之间的关系；（3）生物多样性-生态系统功能范式。通过实施一系列野外和实验室实验，首次在底栖藻类食草作用和/或生态位维度（添加的养分数量 NAN，包括氮、磷、铁和锰）方面进行了操纵，我们有了以下发现。首先， guild 组成的重要预测因子是食草作用（野外）和 NAN（实验室）；丰富度的重要预测因子是 NAN（野外）和 NAN 和 guild 组成（实验室）；均匀度的重要预测因子是 guild 组成（野外和实验室）和食草作用（野外）；生物量的重要预测因子是 guild 组成、NAN、丰富度+均匀度（野外和实验室）。食草作用增加了低轮廓和运动型 guild 的比例，但降低了高轮廓 guild 的比例。在没有放牧的情况下，高轮廓 guild 的比例增加会导致丰富度和生物量增加，但均匀度降低，而在有放牧的情况下，这些关系通常会消失。其次，这两个实验都证实了底栖模型的预测，即物种丰富度随 NAN 增加而增加，这与资源竞争理论不一致。第三，添加锰和/或铁会增加藻类的丰富度，表明在溪流生态学中通常被忽视的微量元素为藻类生态位增加了维度。第四，仅在没有食草作用的情况下观察到的丰富度-均匀度关系取决于物种库的大小。在低于 49 个物种的丰富度（实验室）下，该关系为正，表明存在互补性和促进作用，而在较高的丰富度（野外和实验室）下，该关系为负，与种间负相互作用一致。最后，生物量产生对 guild 组成和 NAN 的依赖程度大于对丰富度和均匀度的依赖程度，这表明需要更全面、更具环境明确性和基于特征的方法来研究生物多样性-生态系统功能范式。
