Data from: Dietary niche constriction when invaders meet natives: evidence from freshwater decapods

1. Invasive species are a key driver of global environmental change, with frequently strong negative consequences for native biodiversity and ecosystem processes. Understanding competitive interactions between invaders and functionally similar native species provides an important benchmark for predicting the consequences of invasion. However, even though having a broad dietary niche is widely considered a key factor determining invasion success, little is known about the effects of competition with functionally similar native competitors on the dietary niche breadths of invasive species. 2. We used a combination of field experiments and field surveys to examine the impacts of competition with a functionally similar native crab species on the population densities, growth rates and diet of the globally widespread invasive red swamp crayfish in an African river ecosystem. 3. The presence of native crabs triggered significant dietary niche constriction within the invasive crayfish population. Further, growth rates of both species were reduced significantly, and by a similar extent, in the presence of one another. In spite of this, crayfish maintained positive growth rates in the presence of crabs, whereas crabs lost mass in the presence of crayfish. Consequently, over the three year duration of the study, crab abundance declined at those sites invaded by the crayfish, becoming locally extinct at one. 4. The invasive crayfish had a dramatic effect on ecosystem structure and functioning, halving benthic invertebrate densities and increasing decomposition rates four-fold compared to the crabs. This indicates that replacement of native crabs by invasive crayfish likely alters the structure and functioning of African river ecosystems significantly. 5. This study provides a novel example of the constriction of the dietary niche of a successful invasive population in the presence of competition from a functionally similar native species. This finding highlights the importance of considering both environmental and ecological contexts in order to predict and manage the impacts of invasive species on ecosystems.1. 外来入侵物种是全球环境变化的关键驱动因素之一，往往会对本地生物多样性与生态系统过程造成显著的负面影响。解析入侵物种与功能相似本土物种间的竞争互作，可为预测生物入侵的后果提供重要基准。然而，尽管宽泛的食性生态位（dietary niche）被广泛视为决定入侵成功的关键因素之一，但目前学界对功能相似的本土竞争者与入侵物种间的竞争如何影响入侵物种的食性生态位宽度仍知之甚少。 2. 本研究结合野外实验与野外调查，于非洲某河流生态系统中，探究了功能相似的本土蟹类与全球广布的入侵性红沼泽螯虾之间的竞争，对螯虾种群密度、生长速率及食性的影响。 3. 本土蟹类的存在会引发入侵螯虾种群的食性生态位显著收缩。此外，当两个物种共存时，二者的生长速率均会出现显著下降，且下降幅度相近。即便如此，螯虾在蟹类共存时仍保持了正生长速率，而蟹类在螯虾共存时则出现了体重下降。因此，在本研究为期三年的周期内，被螯虾入侵的样地中蟹类的丰度持续下降，其中一处样地的蟹类甚至在当地完全灭绝。 4. 与蟹类相比，入侵螯虾对生态系统结构与功能产生了剧烈影响：底栖无脊椎动物的密度降低了一半，分解速率提升了四倍。这表明，入侵螯虾替代本土蟹类，很可能会显著改变非洲河流生态系统的结构与功能。 5. 本研究为成功入侵种群在功能相似本土物种的竞争压力下，其食性生态位发生收缩提供了全新案例。该研究结果凸显了在预测与管控外来入侵物种对生态系统的影响时，同时考量环境与生态背景的重要性。