Populations of generalist fish can be composed of individuals specialised to a small subset of food resources, a process known as individual specialisation. In this study, we hypothesised that variation in the diet and morphology of individuals is related to habitat complexity and that greater levels of individual specialisation are found at intermediate levels of macrophyte biomass. Fish and aquatic plants were sampled in 15 multispecific macrophyte stands with different biomasses in the Baía River (Upper Paraná River floodplain). We assessed habitat complexity using the biomass of aquatic macrophytes (three levels of classification: low, intermediate and high). The diet of Moenkhausia forestii was evaluated with the volumetric method. To assess individual diet specialisation, we used the IS (specialisation index) and NODF (nestedness based on overlap and decreasing fill) index and for individual morphological specialisation we used ecomorphological metrics. We tested for a correlation between diet and morphology with a Mantel test. Contrary to our hypothesis, IS and NODF values indicated greater individual specialisation in the diet of M. forestii from low macrophyte biomass. However, the greatest individual morphological specialisation was found in macrophyte stands with intermediate biomasses. The Mantel test showed that there was no significant correlation between diet and morphology. Thus, individual specialisation of M. forestii diet may be related to an increase in competition (likely intraspecific) in stands with low macrophyte biomass, while morphological specialisation is probably related to greater resources availability and accessibility within stands of intermediate macrophyte biomass.

中文翻译：

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与大型植物有关的鱼类的栖息地复杂性以及饮食和形态的个体差异

通才鱼的种群可以由专门研究一小部分粮食资源的个体组成，这一过程称为个体专门化。在这项研究中，我们假设个体饮食和形态的变化与栖息地的复杂性有关，并且在中等水平的大型植物生物量中发现了更高的个体专长水平。在巴亚河（巴拉那河上游泛滥平原）的15种具有不同生物量的多生大型植物群落中对鱼类和水生植物进行了采样。我们使用水生植物的生物量（三个级别的分类：低，中和高）评估了栖息地的复杂性。林木的饮食用体积法评估。为了评估个体饮食的专业性，我们使用了IS（专业化指数）和NODF（基于重叠和减少的填充物的嵌套度）指数，对于个体形态专业化，我们使用了生态形态学指标。我们通过Mantel测试测试了饮食与形态之间的相关性。与我们的假设相反，IS和NODF值表明来自大型植物生物量较低的Forest M. forestii的饮食具有更大的个体特化性。但是，在具有中间生物量的大型植物群落中发现了最大的个体形态专长。Mantel测试表明饮食与形态之间无显着相关性。因此，M。forestii的个体专业化 饮食可能与低生植物生物量的林分竞争加剧（可能是种内竞争）有关，而形态学专业化可能与中等生植物生物量的林分中较高的资源利用率和可及性有关。