To minimize negative effects of competition, predators must divide resources along one or more niche dimensions. Trophic niche separation is a principal method of resource partitioning in marine environments and is often assessed by quantifying diets of fishes with similar lengths. Taxonomic differences in allometric growth, however, suggest that the degree of gape limitation at a given body size varies among species. We studied resource overlap between two potential competitors in Southeast Alaska: Pacific Halibut Hippoglossus stenolepis and Arrowtooth Flounder Atheresthes stomias. We quantified length–gape relationships and assessed effects of fork length (FL; cm), gape height (GH; mm), and gape width (GW; mm) on interpretations of trophic niche separation. Gape sizes for Arrowtooth Flounder were nearly twice those of Pacific Halibut at similar FLs. Predators with smaller gapes exhibited moderate to high dietary overlap ( = 0.554;  = 0.731), whereas those with larger gapes had lower dietary overlap and distinct diet compositions ( = 0.421;  = 0.265). These findings suggest that the greatest potential for food competition is among small‐bodied Arrowtooth Flounder and relatively large‐bodied Pacific Halibut, with trophic niche separation increasing as these predators progress throughout their ontogeny. When comparing resource use among predators with similar FLs, we found high dietary overlap but significantly different diet compositions ( = 0.657). Thus, we postulate that GW is more appropriate than FL when quantifying trophic niche separation among sympatric fishes, especially when disparate length–gape relationships are detected. Studies of resource partitioning would benefit from examining multiple size metrics and explicitly considering differences in allometric growth, thereby addressing potential mechanisms for resource overlap among hypothesized competitors.

中文翻译：

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大小在阿拉斯加水域中两个底栖鱼类捕食者之间的营养位生态位分离中的作用

为了最大程度地减少竞争的负面影响，掠食者必须沿一个或多个利基维度分配资源。营养位生态位分离是海洋环境中资源分配的一种主要方法，通常通过量化具有相似长度的鱼类的饮食来进行评估。然而，异速生长的分类学差异表明，在给定的体型下，空缺限制的程度因物种而异。我们研究了在阿拉斯加东南部的两个潜在的竞争者之间的资源重叠：太平洋大比目鱼庸stenolepis和箭齿鲽Atheresthes stomias。我们量化了长度与间隙之间的关系，并评估了叉长（FL； cm），间隙高度（GH； mm）和间隙宽度（GW； mm）对营养小生境分离的影响。箭齿比目鱼的间隙尺寸几乎是类似大佛罗里达比目鱼的间隙尺寸的两倍。 差距较小的捕食者的饮食重叠程度中等至较高（= 0.554； 0.731），而差距较大的捕食者的饮食重叠程度较低，饮食组成也不同（ = 0.421； = 0.265）。这些发现表明，食物竞争的最大潜力是在小体箭鱼比目鱼和相对大体的太平洋大比目鱼之间，随着这些掠食者在其整个个体发育过程中的进行，营养位的分离也增加了。在比较具有相似FL的捕食者之间的资源利用时，我们发现膳食重叠率很高，但饮食组成却存在显着差异（ = 0.657）。因此，我们假设在定量同伴鱼类之间的营养生态位分离时，GW比FL更合适，尤其是在检测到不同的长度与缺口之间的关系时。资源分区的研究将受益于检查多个规模指标并明确考虑异速增长的差异，从而解决假设的竞争对手之间资源重叠的潜在机制。