应用脂肪酸组成研究热带东太平洋同域中上层鲨鱼营养生态位分化

Trophic niche partitioning of sympatric pelagic sharks in the tropical Eastern Pacific inferred by fatty acid profiles

物种对食物资源利用方式的差异,即营养生态位分化是物种共存的先决条件之一,对种间营养生态位的比较研究有助于了解同域分布物种的共存机制。脂肪酸组成可反映生物较长时间尺度的摄食信息,对探讨物种间营养生态位分化具有重要指示作用。热带东太平洋主要栖息有8种大型中上层鲨鱼,大青鲨(Prionace glauca)、大眼长尾鲨(Alopias superciliosus)、镰状真鲨(Carcharhinus falciformis)、长鳍真鲨(Carcharhinus longimanus)、浅海长尾鲨(Alopias pelagicus)、尖吻鲭鲨(Isurus oxyrinchus)、路氏双髻鲨(Sphyrna lewini)和锤头双髻鲨(Sphyrna zygaena),通过比较其肌肉脂肪酸组成,分析种间食性差异,营养关系及营养生态位分化。结果表明,尖吻鲭鲨营养级相对较高,大青鲨相对较低。3种鼠鲨与5种真鲨存在食性差异或栖息地隔离。浅海长尾鲨与大眼长尾鲨营养生态位重叠程度较高,存在激烈的资源竞争。大青鲨与镰状真鲨生态位宽度较大,表征其对环境的可塑性较强;尖吻鲭鲨和路氏双髻鲨生态位宽度较小,表现为其食性的特化。本研究解释了脂肪酸组成分析在鲨鱼摄食研究中的潜在应用,对分析大洋性鲨鱼的营养生态位分化,资源分配方式及同域共存机制有一定的应用价值。

Species coexistence depends on how organisms utilize their environmental resources, namely trophic niche partitioning. The comparative study of interspecific trophic niches is helpful for understanding the coexistence mechanism of sympatric species. Fatty acid profiles reflect the feeding information of organisms obtaining a relative long time scale, and play an important role of revealing the trophic niche partitioning among species. There are eight pelagic shark species inhabiting in the tropical Eastern Pacific, including blue shark(Prionace glauca), silky shark(Carcharhinus falciformis), oceanic whitetip shark(C. longimanus), bigeye thresher shark(Alopias superciliosus), pelagic thresher shark(A. pelagicus), shortfin mako shark(Isurus oxyrinchus), scalloped hammerhead shark(Sphyrna lewini), and smooth hammerhead shark(S. zygaena). To study the differences of their feeding habits, nutritional relationship and trophic niche partitioning, the fatty acid profiles of shark muscle tissues were analyzed. Results showed that shortfin mako shark occupied the highest trophic level while blue shark occupied the lowest one. The trophic niche overlap of bigeye thresher shark, pelagic thresher shark and shortfin mako shark indicated their intense prey competition and the spatial segregation compared with other shark species were also detected. Bigeye thresher shark showed the most niche similarity to pelagic thresher shark, indicating they may compete for the same resources. Blue shark and silky shark occupied the largest trophic niche area indicating their strong environmental plasticity. Shortfin mako shark and scalloped hammerhead shark occupied the smallest trophic niche area, which may imply the specialization of their feeding habits and this was proved by their relatively high trophic levels. This study demonstrated the potential application of fatty acid profiles in shark feeding ecology studies, especially in the fields of their trophic niche partitioning, allocation patterns and coexistence mechanism.