Body stoichiometry of heterotrophs: assessing drivers of interspecific variations in elemental composition.

Aim: To document how body stoichiometry of heterotrophs varies globally and to assess phylogenetic, trophic, habitat and body mass drivers of this interspecific variation in elemental composition, focusing on carbon (C), nitrogen (N) and phosphorus (P). Location: Worldwide. Time period: 1930 - 2018. Major taxa studied: Amphibians, fishes (Euteleosteomorpha and Otomorpha), invertebrates, mammals, microbes and sauropsids (birds and reptiles). Methods: We compiled from the scientific literature a global database of body elemental composition of heterotrophs in marine, freshwater and terrestrial realms. We used model selection and ANCOVA analyses to investigate the proportion of variance in elemental composition explained by taxonomic groups, diet, habitat and body mass. We assessed the phylogenetic signal in body stoichiometry using Blomberg9s K and Pagel9s lambda statistics. We assessed the phylogenetic structure of interspecific variation in body stoichiometry using mixed models with nested taxonomic levels as random factors. We finally assessed the co-variation in elemental composition using linear models. Results: Our database currently gathers 17848 independent observations on 1491 species. Body elemental composition was found to be widely variable among species with the four assessed drivers significantly contributing to this variation. Taxonomic group is the strongest contributor to interspecific variance for the stoichiometric traits studied, followed by habitat, diet and body mass. More precisely, stoichiometric traits are generally variable at the three taxonomic levels studied (class, order and family), resulting in a significant but relatively modest phylogenetic signal. Finally, we found significant co-variation among the three body elemental contents, resulting in taxonomic group-specific C:N:P spectrums. Main conclusions: Our global synthesis of body stoichiometry of heterotrophs reveals a strong interspecific variability that is only modestly explained by the species attributes investigated: body mass, habitat and diet. It further reveals that this taxonomically structured residual variation in body stoichiometry seems to be constrained along taxonomic group-specific elemental spectrums.