Data from: Trophic consequences of introduced species: comparative impacts of increased inter-specific versus intra-specific competitive interactions

1. Invasive species can cause substantial ecological impacts on native biodiversity. Whilst ecological theory attempts to explain the processes involved in the trophic integration of invaders into native food webs and their competitive impacts on resident species, results are equivocal. In addition, quantifying the relative strength of impacts from non-native species (inter-specific competition) versus the release of native conspecifics (intra-specific competition) is important but rarely completed. 2. Two model non-native fishes, the globally invasive Cyprinus carpio and Carassius auratus, and the model native fish Tinca tinca, were used in a pond experiment to test how increased intra- and inter-specific competition influenced trophic niches and somatic growth rates. This was complemented by samples collected from three natural fish communities where the model fishes were present. The isotopic niche, calculated using stable isotope data, represented the trophic niche. 3. The pond experiment used additive and substitutive treatments to quantify the trophic niche variation that resulted from intra- and inter-specific competitive interactions. Although the trophic niche sizes of the model species were not significantly altered by any competitive treatment, they all resulted in patterns of inter-specific niche divergence. Increased inter-specific competition caused the trophic niche of T. tinca to shift to a significantly higher trophic position, whereas intra-specific competition caused its position to shift towards elevated δ13C. These patterns were independent of impacts on fish growth rates, which were only significantly altered when inter-specific competition was elevated. 4. In the natural fish communities, patterns of trophic niche partitioning between the model fishes was evident, with no niche sharing. Comparison of these results with those of the experiment revealed the most similar results between the two approaches were for the niche partitioning between sympatric T. tinca and C. carpio. 5. These results indicate that trophic niche divergence facilitates the integration of introduced species into food webs, but there are differences in how this manifests between introductions that increase inter- and intra-specific competition. In entirety, these results suggest that the initial ecological response to an introduction appears to be a trophic re-organisation of the food web that minimises the trophic interactions between competing species.

1. 外来入侵物种会对本地生物多样性造成显著的生态影响。尽管生态学理论试图阐释入侵者融入本地食物网的营养整合过程，以及其对土著物种的竞争影响，但相关研究结果尚无定论。此外，量化非本土物种（种间竞争（inter-specific competition））与本地同种个体释放（种内竞争（intra-specific competition））所产生影响的相对强度，具有重要意义，但此类研究却鲜有开展。
2. 本研究选取两种全球广布的入侵模式非本土鱼类：鲤（Cyprinus carpio）与鲫（Carassius auratus），以及模式本土鱼类丁鱥（Tinca tinca），开展池塘实验以探究种内与种间竞争加剧如何影响营养生态位与体生长速率。同时，本研究采集了存在上述模式鱼类的三个天然鱼类群落的样本作为补充。研究以稳定同位素数据计算得到的同位素生态位，表征营养生态位。
3. 该池塘实验采用添加式与替代式处理，以量化种内与种间竞争相互作用引发的营养生态位变化。尽管所有竞争处理均未显著改变模式物种的营养生态位幅度，但均导致了种间生态位分化的格局。种间竞争加剧会使丁鱥的营养生态位向更高的营养级位置显著偏移，而种内竞争则会使其生态位位置向δ13C升高的方向偏移。上述格局不受鱼类生长速率变化的影响，仅当种间竞争加剧时，鱼类生长速率才会发生显著改变。
4. 在天然鱼类群落中，模式鱼类间的营养生态位分化格局十分显著，不存在生态位共享现象。将上述天然群落的研究结果与池塘实验结果进行对比后发现，两种研究方法得到的最相似结果，是同域分布的丁鱥与鲤之间的生态位分化情况。
5. 上述结果表明，营养生态位分化可促进外来物种融入食物网，但在种间竞争与种内竞争加剧的两类引种事件中，该过程的表现形式存在差异。总体而言，本研究结果显示，外来物种引入后的初始生态响应，似乎是食物网发生营养结构重组，以最小化竞争物种之间的营养相互作用。