Changes in land cover are one of the most extensive and influential human impacts on fluvial ecosystems. In this study, we assessed how changes in food resource quantity and type linked to forest cover affect mountain stream multitrophic macroinvertebrate community size structure. We tested whether the total organism biomass (size spectrum intercept) and the energy transfer efficiency among trophic levels (size spectrum slope) are altered. Community size spectra slopes remained unchanged with variations in food resource type, while intercept increased with resource quantity. This pointed to an internal compensatory regulation of the community size structure for the maintenance of trophic transfer efficiency, only adjusting the total organism biomass to total food resource quantity through variations in organism abundance. Community size structure consistency was related to detritivore-omnivore substitutions, although the shifts in size structure with variations in the degree of allochthony differed between these feeding groups. Omnivore change was numerical (i.e., increase in large organism density with a decrease in allochthony) not related to body size or taxonomic composition. In contrast, detritivores showed a reduction in body size with the decrease in allochthony that did not coincide with a reduction in total biomass or density, but was related to a taxonomic replacement of larger case-building trichopterans by smaller detritivores. These findings elucidate how the size structure of a multitrophic macroinvertebrate community might respond to changes in forest cover, shedding light on the effects of global environmental change on the structure and stability of stream food webs.

中文翻译：

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森林覆盖变化引起的食物资源变化对河流大型无脊椎动物群落规模结构的影响

土地覆盖的变化是人类对河流生态系统影响最广泛和影响最大的一种。在这项研究中，我们评估了与森林覆盖率相关的食物资源数量和类型的变化如何影响山间溪流多营养大型无脊椎动物群落规模结构。我们测试了总生物量（大小谱截距）和营养级之间的能量转移效率（大小谱斜率）是否改变。群落规模谱斜率随着食物资源类型的变化保持不变，而截距随着资源数量的增加而增加。这表明群落大小结构的内部补偿性调节以维持营养转移效率，仅通过生物丰度的变化将生物总生物量调整为食物资源总量。群落大小结构的一致性与食腐动物-杂食动物的替代有关，尽管这些喂养组之间大小结构的变化随异地程度的变化而有所不同。杂食动物的变化是与体型或分类组成无关的数字变化（即大生物密度增加而异地动物减少）。相比之下，碎屑动物的体型随着异地生物的减少而减少，这与总生物量或密度的减少并不相符，而是与较小的碎屑动物在分类学上取代较大的案例构建型三翅目昆虫有关。这些发现阐明了多营养大型无脊椎动物群落的大小结构如何对森林覆盖的变化做出反应，