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.

See Hutchinson et al. 2022 Ecology Letters

DADs_data.RData: Each element in the list is one population-level diet. Element names correspond to the DietID column in DADs_metadata.csv and include the consumer's Latin binomial name as well as the BibTeX key (i.e., the unique identifier of each primary source; reported in the Bibkey column of DADs_metadata.csv and in the DADs_bibliography.bib file). Each population-level diet is a vector describing the percent dietary abundance of each consumed food taxon. 

DADs_bibliography.bib: BibTeX bibliography file containing references for all of the primary sources used to compile the diet data used in our study

DADs_metadata.RData: Metadata for each diet. See Metadata_ReadME.txt for complete descriptions of each variable.

DADSAD_data.RData: Abundances of food taxa in the environments and the diets for six case studies shown in Figure 5 of the article. See DADSAD_ReadMe.txt for further details.