Calculation of dietary niche characteristics using stable isotopes has become a popular approach to understand the functional role of taxa across food webs. An underlying assumption of this approach is that stable isotopes accurately reflect the dietary breadth of a species over a temporal duration defined by tissue-specific isotopic turnover rates. In theory, dietary niche estimates derived from fast turnover rate tissues (e.g., blood plasma and liver) may augment stomach content-derived estimates more agreeably than slower turnover rate tissues (e.g., muscle or fin). We tested this hypothesis by comparing commonly used dietary niche estimates derived from stomach contents (nicheSCA: Levins', Shannon-Wiener's, and Smith's), with those estimated using stable isotopes [nicheSIA: standard ellipse area (SEA), convex hull total area (TA), theta (θ), and ellipse eccentricity (E)] of liver and muscle tissue. Model species were three large-bodied sharks: white (Carcharodon carcharias), dusky (Carcharhinus obscurus), and scalloped hammerhead (Sphyrna lewini). Within-technique comparisons for nicheSCA and nicheSIA metrics (i.e., SEA vs. TA) were often correlated; however, we did not observe any statistically significant correlations between nicheSCA and liver/muscle tissue nicheSIA (i.e., Levins' vs. SEA). We conclude that nicheSCA and nicheSIA do not provide comparable estimates of dietary niche, at least for the three predator species examined. This fundamental discrepancy highlights technique-specific limitations to estimating organismal dietary niche and identifies a need for the use of clearly defined niche metrics, i.e., the standardized use and reporting of the term isotopic niche as proposed by Newsome et al. (Front Ecol Environ 5:429-436, 2007). Finally, further investigation into the factors underpinning nicheSIA is required to better contextualize this popular ecological metric when compared to nicheSCA.

中文翻译：

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你真的吃什么吗 胃含量分析和稳定的同位素比不能统一估计三种海洋捕食者的饮食生态位特征。

使用稳定同位素计算饮食生态位特征已成为了解整个食物网络中分类单元功能作用的一种流行方法。该方法的一个基本假设是，稳定同位素可以准确反映物种在特定组织同位素转换率所定义的时间范围内的饮食宽度。从理论上讲，来自较快周转率组织（例如，血浆或肝脏）的饮食生态位估计值可能比较慢周转率组织（例如，肌肉或鳍）更有利地增加源自胃内容的估计值。我们通过比较常用的从胃中摄取的饮食生态位估计值（nicheSCA：列文斯，香农-维纳和史密斯）与使用稳定同位素[nicheSIA：标准椭圆面积（SEA），凸壳总面积（ TA），θ（θ）和椭圆形偏心率（E）]。模式物种是三种大体鲨鱼：白鲨（Carcharodon carcharias），暗黑鲨（Carcharhinus obscurus）和扇贝锤头（Sphyrna lewini）。通常将nicheSCA和nicheSIA指标（即，SEA与TA）的技术内比较进行关联。但是，我们没有观察到nicheSCA与肝脏/肌肉组织nicheSIA之间有任何统计学上的显着相关性（即Levins与SEA）。我们得出的结论是，nicheSCA和nicheSIA不能提供饮食生态位的可比估计，至少对于所研究的三种捕食动物而言。这种根本的差异突出了估计有机饮食生态位的特定技术限制，并确定了使用明确定义的生态位指标的需求，即 Newsome等人提出的同位素利基一词的标准化使用和报告。（Front Ecol Environ 5：429-436，2007）。最后，与nicheSCA相比，需要进一步研究支撑nicheSIA的因素，以更好地了解这一流行的生态指标。