Dietary abundance distributions: Dominance and diversity in vertebrate diets

<p>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 &gt;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 (<em>sp50</em>, 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 <em>sp50</em> 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 <em>sp50</em> 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.</p>