Using a long time series, we analyzed trends in abundance of two characiform fishes in the upper Parana River and its floodplain: the native Schizodon altoparanae and its alien congener Schizodon borellii, which invaded the floodplain in the last decades. We aimed to contribute to the understanding of the invasive species success and its relationship with its native congener. We compared feeding-related morphology, reproductive investment, and spatial and temporal variations in abundance, searching for possible negative interactions between them. S. altoparanae presented a marked abundance decline between 1986 and 2018, varying with river systems and habitats, but also depending significantly on the abundance of the alien. The native was more abundant in rivers and channels, whereas S. borellii thrived in all habitats, but particularly in channels. Moreover, the alien species, when compared to S. altoparanae, presented relatively larger head depths and mouth gape, and higher values of relative gonadal weight for smaller females. Overall, our results suggest a more generalist habitat use, greater investment in reproduction at small sizes, and larger mouth gape for the invader, which might provide competitive advantages. Although multiple disturbances impact the floodplain, our results suggest that competitive interactions may have contributed to the decline of the native S. altoparanae.

中文翻译：

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新热带河流泛滥平原系统中外来鱼的入侵和本地同类物种的衰落

使用长时间序列，我们分析了巴拉那河上游及其漫滩中两种特征鱼类的丰度趋势：本地 Schizodon altoparanae 及其外来同源物 Schizodon bollii，它们在过去几十年入侵了漫滩。我们的目标是帮助了解入侵物种的成功及其与本土同类的关系。我们比较了与喂养相关的形态、生殖投资以及丰度的时空变化，寻找它们之间可能的负面相互作用。S. altoparanae 在 1986 年至 2018 年之间呈现出显着的丰度下降，随河流系统和栖息地而异，但也显着取决于外来物种的丰度。原生地在河流和渠道中更为丰富，而 S. bollii 在所有栖息地中繁衍生息，尤其是在渠道中。此外，与 S. altoparanae 相比，外来物种呈现出相对较大的头部深度和嘴巴，以及较小雌性的相对性腺重量值较高。总体而言，我们的结果表明，栖息地使用更广泛，对小尺寸繁殖的投资更大，入侵者的嘴巴更大，这可能会提供竞争优势。尽管多重干扰影响了洪泛区，但我们的结果表明，竞争性相互作用可能导致了原生 S. altoparanae 的衰落。入侵者张大嘴巴，这可能会提供竞争优势。尽管多重干扰影响了洪泛区，但我们的结果表明，竞争性相互作用可能导致了原生 S. altoparanae 的衰落。入侵者张大嘴巴，这可能会提供竞争优势。尽管多重干扰影响了洪泛区，但我们的结果表明，竞争性相互作用可能导致了原生 S. altoparanae 的衰落。