Data from: Species richness-productivity relationships of tropical terrestrial ferns at regional and local scales

1. The species richness-productivity relationship (SRPR), by which the species richness of habitats or ecosystems is related to the productivity of the ecosystem or the taxon, has been documented both on regional and local scales, but its generality, biological meaning, and underlying mechanisms remain debated. 2. We evaluated the SRPR and 3 mechanistic hypotheses using terrestrial ferns in 18 study plots along an elevational gradient (500-4000 m) in Ecuador. We measured annual increases in above-ground biomass of 6175 fern individuals from 91 species over 2 years, and estimated plot-level tree productivity from increases in above-ground woody biomass of 560 trees. Analyses were conducted by (a) comparing plots along the elevational gradient (regional scale) and (b) comparing plots within each elevational belt (local scale). 3. Fern diversity was related to the productivity of the fern assemblages, but not to above-ground productivity of the trees. At the regional scale, we found a positive relationship of fern species richness to fern productivity that appeared to be determined by an increase in the number of fern individuals and niche availability. In contrast, at the local scale this relationship was negative and likely driven by interspecific competition. 4. Synthesis: Plot diversity of ferns appears to be limited by the number of available niches and competition to occupy these niches. At the local scale, this is reflected in a negative SRPR probably driven by competition, whereas with increasing scale the positive influence of productivity emerges. This represents the first evidence that productivity and competition affect the diversity of tropical herb assemblages at the plot scale.

1. 物种丰富度-生产力关系（species richness-productivity relationship, SRPR）指生境或生态系统的物种丰富度与生态系统或类群的生产力相关联，该关系已在区域与局域尺度上得到实证记录，但其普适性、生物学内涵与潜在作用机制仍存在学术争议。2. 本研究以厄瓜多尔境内沿海拔梯度（500~4000米）设置的18个样地中的陆生蕨类为研究对象，对SRPR与3种机制假说进行了验证。研究周期为两年，测定了隶属于91个物种的6175株蕨类个体的地上生物量年增量，并通过560株树木的木质地上生物量增量估算了样地水平的树木生产力。分析采用两种方式展开：(a) 对比沿海拔梯度分布的各样地（区域尺度）；(b) 对比每个海拔带内的各样地（局域尺度）。3. 蕨类多样性与蕨类类群的生产力显著相关，但与树木的地上生产力并无关联。在区域尺度上，蕨类物种丰富度与蕨类生产力呈正相关关系，该关系似乎由蕨类个体数量的增加与生态位可利用性提升共同驱动；与之相反，在局域尺度上二者呈负相关关系，其潜在驱动因素大概率为种间竞争。4. 综合结论：蕨类的样地多样性似乎受可用生态位数量与占据这些生态位的种间竞争共同限制。在局域尺度上，这一规律体现为负向的SRPR，其驱动因素大概率为种间竞争；而随着观测尺度扩大，生产力的正向影响逐渐显现。本研究首次提供了实证证据，证明生产力与种间竞争可在样地尺度上调控热带草本类群的多样性。