Resource partitioning in polymorphic fish species is expected to be altered by human exploitation, as individual specialization is density dependent in many vertebrates. We tested this hypothesis using the ballan wrasse Labrus bergylta as a model species. We compared the isotope niches of the plain and spotted morphs of the species in a marine protected area (MPA) and in adjoining areas open to fishing, both off Galicia (NW Spain). Underwater visual census confirmed a 3-fold increase in the biomass of ballan wrasse off the Cíes Islands compared to areas open to recreational fishing, thus demonstrating that populations outside MPAs are well below carrying capacity. The stable isotope ratio of C revealed differences in the resource use patterns of plain and spotted ballan wrasses both in areas open and closed to fishing, as plain wrasses were always depleted in 13C compared to sympatric spotted ones. The stable isotope ratio of N showed that plain ballan wrasses foraged consistently at a higher trophic level than spotted ones in areas of high population density closed to recreational fishing, whereas differences did not exist or were reversed in areas open to fishing. These results demonstrate that the pattern of trophic resource partitioning between 2 morphs of the ballan wrasse is density dependent and that plain and spotted ballan wrasses likely had different ecological niches in pristine ecosystems.

中文翻译：

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捕鱼改变了温带沿海鱼类颜色变体之间的资源分配

多态性鱼类的资源分配预计会因人类开发而改变，因为个体特化在许多脊椎动物中取决于密度。我们使用 Ballan wrasse Labrus bergylta 作为模型物种测试了这一假设。我们在加利西亚（西班牙西北部）附近的海洋保护区 (MPA) 和开放捕鱼的毗邻地区比较了该物种的平原和斑点形态的同位素生态位。水下目测普查证实，与开放休闲捕鱼的区域相比，Cíes 群岛附近的巴兰濑鱼的生物量增加了 3 倍，从而表明海洋保护区以外的种群远低于承载能力。C 的稳定同位素比揭示了在开放和封闭捕鱼区域的平原和斑点巴兰濑鱼的资源利用模式的差异，因为与同域斑点鱼相比，普通濑鱼总是在 13C 中耗尽。N 的稳定同位素比表明，在禁止休闲捕鱼的人口密度高的地区，普通巴兰濑鱼在更高的营养水平上始终如一地觅食，而在开放捕鱼的地区，差异不存在或相反。这些结果表明，巴兰濑鱼 2 种变体之间的营养资源分配模式是密度依赖的，平原和斑点巴兰濑鱼可能在原始生态系统中具有不同的生态位。而在开放捕鱼的地区，差异不存在或相反。这些结果表明，巴兰濑鱼 2 种变体之间的营养资源分配模式是密度依赖的，平原和斑点巴兰濑鱼可能在原始生态系统中具有不同的生态位。而在开放捕鱼的地区，差异不存在或相反。这些结果表明，巴兰濑鱼 2 种变体之间的营养资源分配模式是密度依赖的，平原和斑点巴兰濑鱼可能在原始生态系统中具有不同的生态位。