Resource use by organisms is mainly influenced by factors such as the morphology of individuals and the diversity and abundance of resources. For omnivores, the influence of these factors is more complex, as they have a morphology adapted to access different trophic levels, and any change in the environment can affect the quality or availability of resources. The aim of this study was to evaluate the effect of biotic and abiotic factors on the use of resources by omnivorous fish. We analysed the diet of 107 individuals of Astyanax lineatus in headwater streams in the Pantanal plateau, Brazil. We analysed the influence of body size and the characteristics of streams on the dietary composition, proportion of allochthonous items, trophic niche width and trophic position of individuals. These alimentary parameters were mainly influenced by body size and environmental variables, such as stream vegetation cover, flow, dissolved oxygen and conductivity. Allochthonous resources were more important to the diet of our model fish. We observed that larger individuals are more specialists than medium‐sized individuals and the trophic position decreases with increasing body size. Basically, three factors may have contributed to these results: large supply of carbon‐rich resources; morphology adapted for the consumption of larger, harder and carbon‐rich foods; and the interaction of increased body size and the high temperatures in the Neotropical region that can increase the demand for carbon for energy production.

中文翻译：

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杂食性鱼类的资源利用：生物和非生物因素对个体关键生态方面的影响

生物体对资源的利用主要受到个人形态，资源的多样性和丰富度等因素的影响。对于杂食动物而言，这些因素的影响更为复杂，因为它们具有适应不同营养级别的形态，并且环境的任何变化都可能影响资源的质量或可用性。这项研究的目的是评估杂食鱼类对生物和非生物因素对资源利用的影响。我们分析了107名Astyanax lineatus的饮食在巴西潘塔纳尔高原上游源头的溪流中。我们分析了个体大小和溪流特性对饮食组成，异源食物比例，营养位的宽度和个体营养位置的影响。这些营养参数主要受身体大小和环境变量的影响，例如河流植被覆盖度，流量，溶解氧和电导率。外来资源对我们模型鱼的饮食更为重要。我们观察到，较大的个体比中型个体更有专长，并且随着身体尺寸的增加，营养位置降低。基本上，三个因素可能促成了这些结果：富含碳的资源的大量供应；形态适合于食用更大，更硬和富含碳的食物；