Data from: Competition between co-occurring invasive and native consumers switches between habitats

1. The introduction of a non-native species frequently has adverse direct effects on native species. The underlying mechanisms, however, often remain unclear, in particular where native and invasive species are taxonomically similar. 2. We found evidence of direct competitive interactions between a globally distributed invasive species (the Pacific oyster, Magallana gigas) and its native counterpart (the European oyster, Ostrea edulis). We also discovered that the competitive outcome differed between different habitat types and structures by identifying context-dependent responses driven by environmental conditions and stress (i.e. intertidal compared to subtidal habitats; and vertical versus horizontal substratum). This is particularly important because the European oyster is threatened, or in decline, throughout most of its range and restoration efforts are underway in many regions. 3. We combined experimental manipulations and stable isotope analysis (SIA) to identify the direct effects of competition and the mechanisms by which the invasive and native species compete. We identified negative effects of the invasive species on the native oyster but these were limited to the subtidal habitat (lower stress environment) and determined by substratum orientation (habitat structure). Crucially, we found that effects of the invasive species on the native species were not always negative and under certain conditions (e.g. on vertical substrata) were positive. Shifts in isotopic niches of both species when co-occurring, alongside mixing models, indicate that exploitative competition for food is most likely to underpin niche partitioning between both species. 4. We have identified different foraging strategies under different contexts and our findings highlight the importance of exploitative competition as a driving mechanism behind the co-occurrence of two seemingly functionally similar consumers. The combination of experimental manipulations with SIA is a powerful tool and we illustrate how this approach should be incorporated, into multiple environmental contexts at appropriate scales, to more accurately predict impacts of the spread of invasive species on native communities.1. 外来物种的引入通常会对本土物种产生直接的负面影响，但其背后的作用机制往往尚未阐明，尤其是在本土物种与入侵物种分类学亲缘关系相近的情况下。2. 本研究证实了全球广布入侵物种——太平洋牡蛎（Pacific oyster, *Magallana gigas*）与其本土近缘种欧洲牡蛎（European oyster, *Ostrea edulis*）之间存在直接竞争交互作用。通过解析由环境条件与胁迫驱动的生境依赖响应（即潮间带与潮下带生境、垂直与水平附着基质的差异），我们还发现竞争结局会因不同生境类型与结构而有所差异。这一发现具有重要意义，因为欧洲牡蛎在其绝大多数分布范围内均面临种群威胁或衰退，且目前多个区域已启动其种群修复工作。3. 本研究结合实验操控与稳定同位素分析（stable isotope analysis, SIA），明确了入侵物种与本土物种间竞争的直接效应及其作用机制。我们证实入侵物种对本土牡蛎存在负面影响，但该效应仅局限于潮下带（低胁迫环境），且受基质朝向（生境结构）调控。尤为关键的是，我们发现入侵物种对本土物种的效应并非始终为负，在特定条件下（如垂直基质环境中）甚至可产生积极影响。当两个物种共存时，其同位素生态位的偏移与混合模型分析结果均表明，食物资源的利用性竞争极有可能是二者实现生态位分化的核心驱动机制。4. 本研究明确了不同情境下的差异化觅食策略，研究结果凸显了利用性竞争作为两种功能看似相似的消费者共存核心驱动机制的重要性。实验操控与稳定同位素分析的结合是一种高效且有力的研究手段，我们阐释了该方法应如何在适宜尺度下应用于多环境情境，从而更精准地预测入侵物种扩散对本土群落的生态影响。