Data from: Patterns of trophic niche divergence between invasive and native fishes in wild communities are predictable from mesocosm studies

1. Ecological theory attempts to predict how impacts for native species arise from biological invasions. A fundamental question centres on the feeding interactions of invasive and native species: whether invasion will result in increased interspecific competition, which would result in negative consequences for the competing species, or trophic niche divergence, which would facilitate the invader's integration into the community and their coexistence with native species. 2. Here, the feeding interactions of a highly invasive fish, topmouth gudgeon Pseudorasbora parva, with three native and functionally similar fishes were studied to determine whether patterns of either niche overlap or divergence detected in mesocosm experiments were apparent between the species at larger spatial scales. Using stable isotope analysis, their feeding relationships were assessed initially in the mesocosms (1000 L) and then in small ponds (<400 m2) and large ponds (>600 m2). 3. In the mesocosms, a consistent pattern of trophic niche divergence was evident between the sympatric fishes, with niches shifting further apart in isotopic space than suggested in allopatry, revealing that sharing of food resources was limited. Sympatric P. parva also had a smaller niche than their allopatric populations. 4. In eight small ponds where P. parva had coexisted for several years with at least one of the fish species used in the mesocosms, strong patterns of niche differentiation were also apparent, with P. parva always at a lower trophic position than the other fishes, as also occurred in the mesocosms. Where these fishes were sympatric within more complex fish communities in the large ponds, similar patterns were also apparent, with strong evidence of trophic niche differentiation. 5. Aspects of the ecological impacts of P. parva invasion for native communities in larger ponds were consistent with those in the mesocosm experiments. Their invasion resulted in divergence in trophic niches, partly due to their reduced niche widths when in sympatry with other species, facilitating their coexistence in invaded ecosystems. Our study highlights the utility of controlled mesocosm studies for predicting the trophic relationships that can develop from introductions of non-native species into more complex ecosystems and at larger spatial scales.

1. 生态学理论旨在预测生物入侵对本地物种产生的影响机制。其中一个核心问题聚焦于入侵物种与本地物种的取食相互作用：入侵是否会引发加剧的种间竞争，进而对竞争物种产生负面影响；亦或是发生营养生态位分化，从而助力入侵者融入群落，并与本地物种实现共存。
2. 本研究针对极具入侵性的鱼类——麦穗鱼（Pseudorasbora parva）与三种功能特征相似的本地鱼类开展研究，旨在明确在中型实验生态系统（mesocosm）中观测到的生态位重叠或分化模式，能否在更大空间尺度的生境中于物种间显现。研究首先通过稳定同位素分析（stable isotope analysis），在1000升的中型实验生态系统中评估了这些鱼类的取食关系，随后又在小型池塘（面积<400平方米）与大型池塘（面积>600平方米）中开展了相关评估。
3. 在中型实验生态系统中，同域分布的鱼类间呈现出一致的营养生态位分化模式：同位素空间中的生态位间距相较于异域分布时进一步拉大，表明食物资源的共享程度有限。此外，同域分布的麦穗鱼其生态位宽度也小于异域种群。
4. 在8个已与至少一种实验用本土鱼类共存多年的小型池塘中，同样观测到了显著的生态位分化模式：麦穗鱼的营养级始终低于其他鱼类，这一结果与中型实验生态系统中的发现一致。而在鱼类群落更为复杂的大型池塘中，当这些物种同域分布时，也观测到了类似的模式，并有充分证据表明存在营养生态位分化。
5. 大型池塘中麦穗鱼入侵对本地群落产生的部分生态影响，与中型实验生态系统的研究结果相一致。入侵引发了营养生态位分化，这一定程度上源于同域分布时麦穗鱼的生态位宽度收窄，从而助力其在被入侵生态系统中实现共存。本研究凸显了受控中型实验生态系统研究的价值：其可用于预测将非本土物种引入更复杂生态系统、并在更大空间尺度下可能形成的营养相互关系。