Functional biogeography of dietary strategies in birds

Abstract

Aim Diet is key to understanding resource use by species, their relationships with their environment and biotic interactions. We aimed to identify the major strategies that shape the diet space of birds and to investigate their spatial distributions in association with biogeographical, bioclimatic and anthropogenic drivers. Location Global. Time period Current. Major taxa studied Birds. Methods We analysed score‐based assessments of eight diet categories for 8,937 out of 10,964 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 the positions of species along each dimension for 12,705 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 The diet space of birds was structured by four dimensions ordinating species along continua 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, whereas warm climate, high productivity and high topographic variability 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 continua sustained by morphological and ecophysiological differences among species. Strong biogeographical 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 might, in turn, affect the global distribution of bird functions and services.

Global distribution and conservation status of ecologically rare mammal and bird species

“…Our findings extend this result as we find that the portion of the functional space filled by ecologically rare species does not overlap much that filled by common species, highlighting a functional complementarity, instead of redundancy, between ecologically rare and common species 34 for both mammals and birds. In particular, we show that specific sets of traits were over-contributing to ecological rarity, echoing the results of Barnagaud et al 25 who found that nectarivory, carnivory, and piscivory are rare diets in birds. A significant proportion of ecologically rare mammals and birds are indeed nectarivores or frugivores.…”

“…To that end, worldwide data on Eltonian traits, including the characterization of diet and foraging activity, are relevant candidate features 22 . Global analyses on mammals and birds 20 indeed led to interesting findings about the shape of the functional space of these taxa and about the global distribution of their functional diversity, notably identifying hotspots of functional redundancy [23][24][25][26] . They also highlighted a spatial mismatch between protected areas and taxonomic, phylogenetic, and functional diversity worldwide 27 .…”

“…Here, we defined and assessed the ecological rarity of mammals (4654 species) and birds (9287 species), two threatened vertebrate clades that are largely distributed across the globe and support important ecological functions in ecosystems such as seed dispersal, trophic interaction, and nutrient cycling 25,26 . For each species, we estimated ecological rarity as a combination of geographical restrictiveness and functional distinctiveness.…”

Search for top-down and bottom-up drivers of latitudinal trends in insect herbivory in oak trees in Europe

“…ants, ladybirds) are much more abundant at lower latitudes, resulting in a higher selection pressure toward the equator (Roslin et al, 2017). Second, bird communities are more influenced by forest habitat composition at lower latitudes, and more by food availability at higher latitudes (Charbonnier et al, 2016) where the diet variability is lower (Barnagaud et al, 2019), suggesting a stronger effect of local habitat features (e.g. resource availability and habitat suitability) than climatic gradients.…”

Global functional and phylogenetic structure of avian assemblages across elevation and latitude

“…Deviations of functional from phylogenetic structure are likely to occur in birds because avian traits show pervasive convergent evolution (Pigot et al ., 2020), with several morphological trait combinations (Pigot et al ., 2020) and dietary characteristics (Kissling et al ., 2012) having multiple origins within the clade. Dietary traits also show differential associations with phylogenetic structure (Barnagaud et al ., 2019), with nectarivory, frugivory and insectivory being associated with phylogenetic overdispersion, while carnivory being phylogenetically clustered (Barnagaud et al ., 2014), although it is unknown whether these traits show similar relationships with functional structure. Evaluating the association between functional and phylogenetic structure on a global scale, and potential factors in its variation, can help assess their surrogacy for basic and applied questions and hint at ecological and evolutionary causes of assemblage composition (Devictor et al ., 2010; Graham et al ., 2012; Gerhold et al ., 2015; Mazel et al ., 2018, but see Mayfield and Levine, 2010; Cadotte and Tucker, 2017).…”