1. Amphipod crustaceans are ubiquitous in temperate freshwaters, where they radiated multiple times in a broad range of habitats. This has led to significant morphological and ecological disparity. However, a limited knowledge of functional morphology and its relation to ecology has often led to the view that freshwater amphipods are omnivorous shredders. Herein, we hypothesise that trophic differentiation is related to functional morphology in a sympatric assemblage of three species belonging to three widespread families: Crangonyctidae, Gammaridae, and Niphargidae.
2. We quantified seasonal diet composition by examining gut contents, and measured 42 functional morphological traits.
3. Our results reveal a clear trophic and morphological differentiation among these sympatric species. The carnivorous Niphargus valachicus exhibited predatory traits exemplified by a smaller molar surface and stomach length, and larger/longer grasping, locomotory, and sensory appendages in comparison to the herbivorous Gammarus dacicus. The third species, Synurella ambulans, was omnivorous given its intermediate diet and morphology. We did not find consistent evidence for seasonal diet variation, except for the summer and winter diet of G. dacicus.
4. The observed niches stretched along a broad trophic spectrum, indicating that even small riverine amphipod communities can exhibit significant functional disparity.
5. The apparent connection between morphology and diet is similar to that observed in other crustaceans, strengthening our mechanistic understanding of the niche–morphology link. However, the generality of these conclusions needs to be tested on larger species datasets.

中文翻译：

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形态学反映了淡水片脚类群落的营养生态位

1. 片脚类甲壳类动物在温带淡水中无处不在，它们在广泛的栖息地中多次辐射。这导致了显着的形态和生态差异。然而，对功能形态及其与生态关系的有限了解常常导致人们认为淡水片脚类动物是杂食动物。在此，我们假设营养分化与属于三个广泛家族的三个物种的同域组合中的功能形态有关：Crangonyctidae、Gammaridae 和 Niphargidae。
2. 我们通过检查肠道内容量化了季节性饮食组成，并测量了 42 种功能形态特征。
3. 我们的结果揭示了这些同域物种之间明显的营养和形态差异。与草食性Gammarus dacicus相比，肉食性Niphargus valachicus表现出掠食性特征，例如更小的臼齿表面和胃长度，以及更大/更长的抓握、运动和感觉附属物。第三个物种，Syurella ambulans，考虑到它的中间饮食和形态，是杂食性的。除了G. dacicus的夏季和冬季饮食外，我们没有发现季节性饮食变化的一致证据。
4. 观察到的生态位沿着广泛的营养谱延伸，表明即使是小型的河流片脚类群落也可能表现出显着的功能差异。
5. 形态和饮食之间的明显联系与在其他甲壳类动物中观察到的相似，加强了我们对生态位-形态联系的机制理解。然而，这些结论的普遍性需要在更大的物种数据集上进行测试。