Data from: Limited trophic partitioning among sympatric delphinids off a tropical oceanic atoll

Understanding trophic relationships among marine predators in remote environments is challenging, but it is critical to understand community structure and dynamics. In this study, we used stable isotope analysis of skin biopsies to compare the isotopic, and thus, trophic niches of three sympatric delphinids in the waters surrounding Palmyra Atoll, in the Central Tropical Pacific: the melon-headed whale (Peponocephala electra), Gray’s spinner dolphin (Stenella longirostris longirostris), and the common bottlenose dolphin (Tursiops truncatus). δ15N values suggested that T. truncatus occupied a significantly higher trophic position than the other two species. δ13C values did not significantly differ between the three delphinds, potentially indicating no spatial partitioning in depth or distance from shore in foraging among species. The dietary niche area—determined by isotopic variance among individuals—of T. truncatus was also over 30% smaller than those of the other species taken at the same place, indicating higher population specialization or lower interindividual variation. For P. electra only, there was some support for intraspecific variation in foraging ecology across years, highlighting the need for temporal information in studying dietary niche. Cumulatively, isotopic evidence revealed surprisingly little evidence for trophic niche partitioning in the delphinid community of Palmyra Atoll compared to other studies. However, resource partitioning may happen via other behavioral mechanisms, or prey abundance or availability may be adequate to allow these three species to coexist without any such partitioning. It is also possible that isotopic signatures are inadequate to detect trophic partitioning in this environment, possibly because isotopes of prey are highly variable or insufficiently resolved to allow for differentiation.在偏远海域探究海洋捕食者间的营养关系（trophic relationships）极具挑战，但对于理解群落结构与动态而言至关重要。本研究采用皮肤活检样本的稳定同位素分析（stable isotope analysis），对比了中热带太平洋帕尔米拉环礁（Palmyra Atoll）周边海域三种同域分布的海豚科动物（delphinids）的同位素特征，进而解析其营养生态位（trophic niche）：瓜头鲸（*Peponocephala electra*，melon-headed whale）、格雷氏飞旋海豚（*Stenella longirostris longirostris*，Gray’s spinner dolphin）以及普通宽吻海豚（*Tursiops truncatus*，common bottlenose dolphin）。 δ¹⁵N值显示，普通宽吻海豚的营养级（trophic position）显著高于另外两个物种。三种海豚科动物的δ¹³C值无显著差异，这可能意味着它们在觅食时的水深或离岸距离不存在空间分化（spatial partitioning）。由个体间同位素方差计算得到的普通宽吻海豚饮食生态位面积（dietary niche area），也比同区域采样的另外两个物种小30%以上，表明其种群特化程度更高，或个体间觅食差异更低。 仅在瓜头鲸种群中，观测到了不同年份间觅食生态存在种内变异（intraspecific variation）的相关证据，这凸显了在研究饮食生态位时纳入时间维度信息的必要性。总体而言，与其他相关研究相比，本研究的同位素证据表明，帕尔米拉环礁的海豚科群落几乎未出现营养生态位分化（trophic niche partitioning）。 不过，资源分化可能通过其他行为机制实现，或是猎物丰度与可获得性足以支撑这三个物种共存，无需此类营养生态位分化。也有可能是同位素标记不足以在该环境中检测到营养生态位分化，原因可能是猎物的同位素特征变异度极高，或是分辨率不足，无法实现物种间的区分。