Data from: Functional traits and environmental conditions predict community isotopic niches and energy pathways across spatial scales

1. Despite ongoing research in food web ecology and functional biogeography, the links between food-web structure, functional traits and environmental conditions across spatial scales remain poorly understood. Trophic niches, defined as the amount of energy and elemental space occupied by species and food webs, may help bridge this divide. 2. Here, we ask how the functional traits of species, the environmental conditions of habitats and the spatial scale of analysis jointly determine the characteristics of trophic niches. We used isotopic niches as a proxy of trophic niches, and conducted analyses at spatial scales ranging from local food webs and metacommunities to geographically distant sites. 3. We sampled aquatic macroinvertebrates from 104 tank bromeliads distributed across five sites from Central to South America, and compiled the macroinvertebrates’ functional traits and stable isotope values (δ15N and δ13C). We assessed how isotopic niches within each bromeliad were influenced by the functional trait composition of their associated invertebrates and environmental conditions (i.e., habitat size, canopy cover, and detrital concentration). We then evaluated whether the diet of dominant predators and, consequently, energy pathways within food webs, reflected functional and environmental changes among bromeliads across sites. Finally, we determined the extent to which the isotopic niches of macroinvertebrates within each bromeliad contributed to the metacommunity isotopic niches within each site, and compared these metacommunity-level niches over biogeographic scales. 4. At the bromeliad level, isotopic niches increased with the functional richness of species in the food web and the detrital concentration in the bromeliad. The diet of top predators tracked shifts in prey biomass along gradients of canopy cover and detrital concentration. Bromeliads that grew under heterogeneous canopy cover displayed less trophic redundancy and therefore combined to form larger metacommunity isotopic niches. Finally, the size of metacommunity niches depended on within-site heterogeneity in canopy cover. 5. Our results suggest that the trophic niches occupied by food webs can predictably scale from local food webs to metacommunities to biogeographic regions. This scaling process is determined by both the functional traits of species and heterogeneity in environmental conditions.

1. 尽管当前食物网生态学（food web ecology）与功能生物地理学（functional biogeography）领域已开展大量研究，但不同空间尺度下食物网结构、功能性状与环境条件之间的关联仍未得到充分阐释。营养生态位（trophic niches）被定义为物种及食物网所占据的能量与元素空间，或可成为打通这一研究鸿沟的关键桥梁。
2. 本研究旨在探究物种功能性状、栖息地环境条件与分析空间尺度三者如何共同决定营养生态位的特征。我们以同位素生态位（isotopic niches）作为营养生态位的替代指标，并在从局地食物网、集合群落（metacommunities）到地理偏远样点的多空间尺度上开展分析。
3. 我们从中美洲至南美洲的5个样点中，采集了104株积水凤梨（tank bromeliads）内的水生大型无脊椎动物（aquatic macroinvertebrates），并整理了该类无脊椎动物的功能性状数据与稳定同位素值（δ¹⁵N和δ¹³C）。我们评估了每株积水凤梨内部的同位素生态位如何受其伴生无脊椎动物的功能性状组成，以及生境大小、冠层覆盖度、碎屑浓度等环境条件的影响。随后，我们分析了优势捕食者的食谱及由此形成的食物网能量通路，是否能反映不同样点间积水凤梨的功能与环境变化。最后，我们明确了每株积水凤梨内的大型无脊椎动物同位素生态位对对应样点内集合群落同位素生态位的贡献程度，并在生物地理尺度上比较了各集合群落水平的生态位特征。
4. 在积水凤梨尺度下，同位素生态位随食物网内物种的功能丰富度（functional richness）以及积水凤梨内部碎屑浓度的升高而扩大。顶级捕食者的食谱会随着冠层覆盖度与碎屑浓度的梯度变化，追踪猎物生物量的变动。冠层覆盖异质性较高的积水凤梨，其营养冗余（trophic redundancy）更低，因此这类积水凤梨共同构成了更大的集合群落同位素生态位。最终，集合群落生态位的大小取决于样点内冠层覆盖度的异质性。
5. 本研究结果表明，食物网所占据的营养生态位可按照可预测的规律，从局地食物网扩展至集合群落，乃至生物地理区域。这一尺度转换过程同时由物种的功能性状与环境条件异质性共同决定。