Résumé
Aim: Diet is key to understanding species’ resource use, relationships
with their environment and biotic interactions. We aimed to identify the
major strategies that shape birds’ diet space, and to investigate their
spatial distributions in association with biogeographic, bioclimatic and
anthropogenic drivers. Location: Global Time period: Current Major taxa
studied: Birds Methods: We analysed score-based assessments of eight diet
categories for 8937 out of 10964 extant bird species. We constructed a
multivariate diet space by ordinating these data in a principal
coordinates analysis, and assessed its dimensionality as a balance between
the representation of original diet scores and parsimony. We averaged
species’ positions along each dimension for 12705 species assemblages and
used quantile regressions to infer the relative contributions of species
richness, climate, primary productivity, topography and human footprint to
the spatial distribution of the diet space at a global scale. Results:
Birds’ diet space was structured by four dimensions ordinating species
along continuums ranging from insectivory to plant-based strategies,
granivory to frugivory, common to rare diets and nectarivory to carnivory
and piscivory. Although orthogonal at the species level, these dimensions
were correlated among species assemblages, with regional variation
consistent with past climatic and tectonic events. Human footprint packed
bird assemblages in the diet space, while warm climate, high productivity
and high topography were associated with high variability in the
prevalence of dietary strategies among assemblages. Main conclusions: The
tremendous variability in bird diets can be explained by a few basic
ecological continuums sustained by morphological and ecophysiological
differences among species. Strong biogeographic legacies on top of
bioclimatic drivers distribute this diet space in species assemblages
through environmental filtering and niche packing. However, these patterns
are altered at macroecological scales by human-mediated functional
homogenization, which may in turn affect the global distribution of bird
functions and services.