Ricerc@Sapienza

In biodiversity studies a species is often classified as original when it has few closely related species, a definition
that reflects its phylogenetic originality. More recently, studies have focussed on biological or functional traits
that reflect the role(s) that species play within communities and ecosystems. This has led many studies to an
alternative evaluation of species’ originality: its functional originality. Most indices of species' originality were
developed to treat the hierarchical structure of a (phylogenetic) tree. The change in perspective from measures of
phylogenetic originality to measures of functional originality thus raises methodological issues particularly
around the need to develop indices explicitly appropriate for evaluating functional trait-based originality. We
compare indices of species' originality including a new index which we develop to evaluate (1) whether phylogenetic
originality could serve as a proxy for functional originality in conservation and ecological studies; (2)
whether the transformation of functional data into functional trees modifies the way species are ranked according
to their originality measures compared to approaches that directly rely on pairwise functional dissimilarities
among species; and more generally, (3) whether different indices provide different views on how original
species are from each other, hence reflecting different ecological and evolutionary processes that generated
patterns of originality. Using simulations and a real case study, we show that: (1) the strong effects of the choice
of a clustering approach can affect reported levels of dissimilarities among species; (2) the tree-based approaches
could better reflect the trait-generating processes under constant (Brownian) rates of evolution; and (3) phylogenetic
originality measures can depart from functional originality measures when species have large amount
of independent evolution. Overall, phylogenies may be used at large scales but cannot replace functional approaches
designed for depicting community assembly. Indeed, traits involved in ecological processes may have
various histories and thus moderate phylogenetic signals. Our comparative study provides approaches and
perspectives on the analysis of originality across biological scales of organization from individuals, through
populations, up to the originalities of communities and regions.