Abstract

Dietary descriptions based on stomach content are pervasive regardless of the biases concerning its methodology, statistics and descriptors. We here review different biases on the stomach content analysis, sample size, and indices used for cephalopods. These mollusks are key components in marine food webs and most are characterized as active predators, thus, knowledge of their feeding ecology based on stomach content analysis is of paramount importance. We suggest alternatives to describe dietary data using unbiased estimators. These are based on re-sampling, using published data of cephalopod stomach content, and conducting estimations using intervals. In our review, we detected that several studies found a high proportion of empty stomachs and highly digested preys, which influences the sample size with contents. In turn, sample size is positively associated with the number of prey species in the stomach contents. Moreover, many studies confuse the terms opportunistic vs. generalist predator and selective vs. specialist predator. Therefore, to improve the understanding of these concepts, we calculated niche-width indices and compared them with prey richness and evenness at individual and population levels. We also show that although most cephalopods exhibit generalized diet and wide trophic niche, their hunting strategy is selective and specialized at individual level. It is worth noting that the diet of over 90% of cephalopod species is not yet known, and thus, the number of trophic studies should increase to fill this gap of knowledge. We provide a series of recommendations to improve and correctly conduct and interpret the studies of stomach content for cephalopods.

Graphical abstract

中文翻译：

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头足类动物的胃内容物分析：过去的研究，当前的挑战和未来的方向

摘要

基于胃内容物的饮食描述无处不在，无论其方法学，统计学和描述因素有何偏见。我们在这里回顾了对胃内容物分析，样本量和用于头足类动物的指数的不同偏见。这些软体动物是海洋食物网中的关键成分，大多数被定性为活跃的捕食者，因此，基于胃内容物分析了解它们的摄食生态学至关重要。我们建议使用无偏估计量来描述饮食数据的替代方法。这些是基于重新采样，使用头足类胃内容物的公开数据并使用间隔进行估计。在我们的综述中，我们发现有几项研究发现高比例的空腹和高度消化的猎物，这会影响样品的含量。反过来，样本量与胃内容物中猎物种类的数量呈正相关。而且，许多研究使术语机会主义混淆了对抗普通捕食者和选择性对抗专家捕食者。因此，为了增进对这些概念的理解，我们计算了利基宽度指数，并将它们与个体和人口水平上的猎物丰富度和均匀度进行了比较。我们还表明，尽管大多数头足类动物都具有普遍的饮食和丰富的营养生态位，但它们的狩猎策略是选择性的，并且在个体水平上是专门的。值得注意的是，目前尚不知道90％以上的头足类动物的饮食，因此，应增加营养研究的数量以填补这一知识空白。我们提供了一系列建议，以改善和正确地进行和解释头足类动物的胃内容研究。

图形概要