Dietary abundance distributions: Dominance and diversity in vertebrate diets

Diet composition is among the most important yet least understood
dimensions of animal ecology. Inspired by the study of species-abundance
distributions (SADs), we tested for generalities in the structure of
vertebrate diets by characterizing them as dietary-abundance distributions
(DADs). We compiled data on 1167 population-level diets, representing
>500 species from 6 vertebrate classes, spanning all continents and
oceans. DADs near-universally (92.5%) followed a hollow-curve shape, with
scant support for other plausible rank-abundance-distribution shapes. This
strong generality is inherently related to, yet incompletely explained by,
the SADs of available food taxa. By quantifying dietary generalization as
the half-saturation point of the cumulative distribution of dietary
abundance (sp50, minimum number of foods required to account for 50% of
diet), we found that vertebrate populations are surprisingly specialized:
in most populations, fewer than three foods accounted for at least half
the diet. Variation in sp50 was strongly associated with consumer type,
with carnivores being more specialized than herbivores or omnivores. Other
methodological (sampling method and effort, taxonomic resolution),
biological (body mass, frugivory), and biogeographic (latitude) factors
influenced sp50 to varying degrees. Future challenges include identifying
the mechanisms underpinning the hollow-curve DAD, its generality beyond
vertebrates, and the biological determinants of dietary generalization.

饮食组成是动物生态学中最为重要却又研究最为薄弱的维度之一。受物种多度分布（species-abundance distributions, SADs）的研究启发，我们将脊椎动物的饮食特征化为饮食多度分布（dietary-abundance distributions, DADs），以此检验其结构是否存在通用规律。我们共收集了1167份种群级饮食数据，涵盖6个脊椎动物纲的500余个物种类群，覆盖全球所有大陆与海洋。饮食多度分布近乎普遍（占比92.5%）呈现中空曲线形态，几乎没有证据支持其他合理的秩多度分布形态。这种显著的通用性与可获取食物类群的物种多度分布存在内在关联，但无法完全由后者解释。我们将饮食泛化程度量化为饮食多度累积分布的半饱和点（sp50，即占饮食总量50%所需的最少食物类群数量），结果发现脊椎动物种群的特化程度出人意料：多数种群仅需不到3种食物类群即可满足其一半的饮食需求。sp50的数值差异与取食类型密切相关，食肉动物的特化程度高于草食动物与杂食动物。其他方法学因素（采样方法与采样强度、分类学分辨率）、生物学因素（体重、食果性）以及生物地理因素（纬度）均会在不同程度上影响sp50。未来的研究挑战包括阐明支撑中空曲线型饮食多度分布的内在机制、验证其在脊椎动物类群之外的通用性，以及揭示饮食泛化程度的生物学决定因素。