Data from: Separation of realized ecological niche axes among sympatric tilefishes provides insight into potential drivers of co‐occurrence in the NW Atlantic

Golden and Blueline Tilefish (Lopholatilus chamaeleonticeps and Caulolatilus microps) are keystone taxa in northwest (NW) Atlantic continental shelf‐edge environments due to their biotic (trophic‐mediated) and abiotic (ecosystem engineering) functional roles combined with high‐value fisheries. Despite this importance, the ecological niche dynamics (i.e., those relating to trophic behavior and food‐web interactions) of these sympatric species are poorly understood, knowledge of which may be consequential for maintaining both ecosystem function and fishery sustainability. We used stable isotope ratios of carbon (δ13C) and nitrogen (δ15N) to build realized ecological niche hypervolumes to serve as proxies for diet and production use patterns of L. chamaeleonticeps and C. microps. We hypothesized that: (a) species exhibit ontogenetic shifts in diet and use of production sources; (b) species acquire energy from spatially distinct resource pools that reflect a sedentary life‐history and differential use of the continental shelf‐edge; and (c) species exhibit differentiation in one or more measured niche axes. We found evidence for ontogenetic shifts in diet (δ15N) but not production source (δ13C) in both species, suggesting a subtle expansion of measured ecological niche axes. Spatial interpolation of stable isotope ratios showed distinct latitudinal gradients; for example, individuals were 13C enriched in northern and 15N enriched in southern regions, supporting the assertion that tilefish species acquire energy from regional resource pools. High isotopic overlap was observed among species (≥82%); however, when hypervolumes included depth and region of capture, overlap among species substantially decreased to overlap estimates of 15%–77%. This suggests that spatial segregation could alleviate potential competition for resources among tilefish species inhabiting continental shelf‐edge environments. Importantly, our results question the consensus interpretation of isotopic overlap estimates as representative of direct competition among species for shared resources or habitats, instead of identifying habitat segregation as a possible mechanism for the coexistence of tilefish species in the NW Atlantic.

金带方头鱼与蓝线方头鱼（学名分别为Lopholatilus chamaeleonticeps与Caulolatilus microps）是西北大西洋大陆架边缘生境中的关键类群（keystone taxa），兼具生物（营养介导）与非生物（生态系统工程）功能角色，同时具备高经济渔业价值。尽管此类群具有如此重要性，但这两种同域分布物种的生态位动态（即与营养行为、食物网互作相关的动态）仍鲜有研究，而相关认知对于维持生态系统功能与渔业可持续性均具有重要意义。
本研究利用碳（δ¹³C）与氮（δ¹⁵N）稳定同位素比值（stable isotope ratios），构建现实生态位超体积（realized ecological niche hypervolumes），以此作为两种方头鱼食谱与资源利用模式的替代指标。我们提出以下研究假说：（a）两个物种在食谱与资源来源利用上均存在个体发育转变（ontogenetic shifts）；（b）物种从空间上分化的资源库获取能量，这反映了其定居型生活史以及对大陆架边缘生境的差异化利用；（c）两个物种在至少一个测定的生态位轴上存在分化。
研究结果显示，两种方头鱼的食谱（以δ¹⁵N为指示）均存在个体发育转变，但资源来源利用（以δ¹³C为指示）未出现此类变化，这表明测定的生态位轴存在微弱扩张。稳定同位素比值的空间插值分析显示出显著的纬度梯度：例如，北部区域的个体碳13富集程度更高，而南部区域的个体氮15富集程度更高，这支持了方头鱼从区域资源库获取能量的论断。物种间的同位素生态位重叠度较高（≥82%）；然而，当超体积模型纳入捕获深度与捕获区域后，物种间的重叠度大幅下降至15%~77%。这表明空间分隔或可缓解栖息于大陆架边缘生境的方头鱼物种间的潜在资源竞争。
尤为重要的是，本研究结果对“同位素重叠度可代表物种间共享资源或生境的直接竞争”这一主流解读提出了质疑，转而证实生境分隔或是西北大西洋方头鱼物种得以共存的潜在机制。