Data from: Do deposit-feeders compete? Isotopic niche analysis of an invasion in a species-poor system

Successful establishment of invasive species is often related to the existence of vacant niches. Competition occurs when invaders use the same limiting resources as members of the recipient community, which will be reflected in some overlap of their trophic niches. The concept of isotopic niche has been used to study trophic niche partitioning among species. Here, we present a two-year field study comparing isotopic niches of the deposit-feeding community in a naturally species-poor system. The isotopic niche analyses showed no overlap between a recent polychaete invader and any of the native species suggesting that it has occupied a vacant niche. Its narrow isotopic niche suggests specialized feeding, however, the high d15N values compared to natives are most likely due to isotope fractionation effects related to nitrogen recycling and a mismatch between biological stoichiometry of the polychaete and the sediment nitrogen content. Notably, highly overlapping isotopic niches were inferred for the native species, which is surprising in a food-limited system. Therefore, our results demonstrate that invaders may broaden the community trophic diversity and enhance resource utilization, but also raise questions about the congruence between trophic and isotopic niche concepts and call for careful examination of assumptions underlying isotopic niche interpretation.

入侵物种的成功定殖通常与空白生态位的存在密切相关。当入侵者与接收群落的成员利用相同的限制性资源时，便会产生种间竞争，这一现象会体现在二者营养生态位的部分重叠上。同位素生态位（isotopic niche）这一概念已被用于研究物种间的营养生态位分化。本研究开展了为期两年的野外调查，对比了自然物种贫乏系统中食底泥群落的同位素生态位。同位素生态位分析结果显示，近期入侵的多毛类动物与所有本地物种的同位素生态位均无重叠，表明该入侵者已占据了一个空白生态位。该入侵者狭窄的同位素生态位暗示其取食具有特化性；不过，与本地物种相比其较高的δ¹⁵N值，极有可能源于与氮循环相关的同位素分馏效应，以及多毛类的生物化学计量与沉积物氮含量之间的不匹配。值得注意的是，研究推断本地物种间的同位素生态位存在高度重叠，这在食物受限的系统中颇为出人意料。综上，本研究结果表明，入侵物种可能会提升群落的营养多样性并强化资源利用效率，但同时也引发了关于营养生态位与同位素生态位概念一致性的疑问，并呼吁学界审慎审视同位素生态位解读背后的各项假设。