The effects of invaders on native species are usually tested using species mean trait values over long time scales. However, considering individual variation over short timescales can help us better understand the interaction between invaders and native species. We compared trophic traits of the non-native guppy (Poecilia reticulata) and the native Brazilian poeciliid Phalloceros harpagos using experiments simulating the early stages of an invasive process. We used short-term mesocosms to simulate an early invasion scenario, where the two species were placed together, and a pre-invasion scenario, where species were kept separated, and analyzed interspecific and intraspecific trophic variability. We also compared the foraging efficiency of species in laboratory experiments. We found no differences on the mean diet of both species between pre and early invasion treatments. At the individual level, in the early invasion scenario, individuals of both species reduced their trophic niche as a probable effect of the presence of the heterospecific. Phalloceros harpagos had higher consumption rates than guppies indicating greater efficiency in feeding on invertebrates. Our results suggest that non-native species were not intrinsically better consumers of high-quality resources. Instead, intraspecific variation might be playing an overlooked role in shaping interactions between species during the early stages of invasion.

入侵者对本地物种的影响通常使用长期尺度上的物种平均性状值进行测试。但是，考虑短期内的个体差异可以帮助我们更好地了解入侵者与本地物种之间的相互作用。我们比较了非原生孔雀鱼（Poecilia reticulata）和巴西本土的poeciliid Phalloceros harpagos的营养特性使用模拟入侵过程早期阶段的实验。我们使用短期内观来模拟将两种物种放在一起的早期入侵场景，以及将物种保持分离的入侵前场景，并分析种间和种内营养变异性。我们还比较了实验室实验中物种的觅食效率。我们发现入侵前和入侵治疗前两种物种的平均饮食没有差异。在个体层面上，在早期入侵的情况下，这两种物种的个体都减少了其营养位，这是由于存在异种特异性的可能影响。哈氏草alloc孔雀鱼的食用率要高于孔雀鱼，这表明它们以无脊椎动物为食的效率更高。我们的结果表明，非本地物种并不是优质资源的内在更好的消费者。取而代之的是，在入侵的早期阶段，种内变异可能在塑造物种之间的相互作用中起着被忽视的作用。