Résumé
Aim : Investigations into how different facets of biodiversity are related has becomea central research agenda in ecology. Here, we use a large-scale and high-resolutiondata set on bird distribution to examine the robustness of the relationships betweenspecies diversity and functional or phylogenetic diversity.LocationFranceMethodsWe measured the functional and phylogenetic diversity of 1914 birdassemblages monitored over 10 years with a standardized protocol. We investigatedthe consequences of incorporating abundance versus presence–absence data,changing the number and identity of traits considered, or varying the spatial scaleused to estimate functional and phylogenetic diversity. We further examined theoutcomes of different null model procedures that aim to reveal ecological processesinfluencing the distribution of each facet of diversity.ResultsWe found that the shape and strength of the relationship between speciesdiversity and functional diversity are structured by several methodological choices.We show that increasing the quantity of information yielded by the indices (inparticular, including abundances or increasing the number of traits considered)decreases the amount of functional redundancy estimated. Reducing the number offunctional traits used to estimate functional diversity can change and even reversethe relationship of interest. Moreover, using alternative null models, we highlightedthe specific role of environmental filtering and the link between species abundancesand their functional originality (defined for a given species as the average of thefunctional distances with other species). The same tests applied to phylogeneticdiversity revealed that its relationship with species diversity varies differently sug-gesting that this latter index cannot be used as a proxy for functional diversity.Main conclusionsOur results show that the identification of patterns and pro-cesses linking species diversity to functional or phylogenetic diversity vary withmethodological choices. We further show that the study of these sources of vari-ation via robustness tests allows ecologically meaningful information to be sepa-rated from pure artefacts.