Assessing biodiversity with sound: Do acoustic diversity indices reflect phylogenetic and functional diversities of bird communities?

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Measuring biodiversity is a challenging task for research in taxonomy, ecology and conservation. Biodiversity is commonly measured using metrics related to species richness, phylogenetic-, or functional-trait diversity of species assemblages. Because these metrics are not always correlated with each other, they have to be considered separately. A descriptor of animal diversity based on the diversity of sounds produced by animal communities, named here the Community Acoustic Diversity (CAD), was recently proposed. In many cases, the CAD could be easier to measure than other metrics. Although previous analyses have revealed that acoustic diversity might increase as species richness increases, the ability of CAD to reflect other components of biodiversity has not been formally investigated. The aim of this study is to test theoretically whether functional and phylogenetic diversities could be reflected by acoustic diversity indices in bird communities. Data on species assemblages were collated by the French Breeding Bird Survey describing spatial and temporal variation in community structure and composition across France since 2001. Phylogenetic and functional data were compiled from literature. Acoustic data were obtained from sound libraries. For each of the 19,420 sites sampled, indices of phylogenetic, functional and acoustic diversity of bird communities were calculated based on species’ pair-wise distance matrices and species’ abundances. The different aspects of biodiversity were compared through correlation analyses. The results showed that acoustic diversity was correlated with phylogenetic diversity, when the branch lengths of the tree were considered, and to functional diversity, especially body mass and reproduction. Correlations between phylogenetic, functional and acoustic distances among species did not entirely explain the correlations between phylogenetic, functional and acoustic diversity within communities. This result was interpreted as an effect of local ecological processes underpinning how bird communities assemble. Comparing the diversity patterns with a null model, phylogenetic and functional diversities were significantly clustered whereas acoustic diversity was not different from what was expected by chance. A comparison between acoustic indices showed that spectral component of acoustic diversity seems more appropriate to reveal bird phylogenetic diversity whereas temporal component seems more adapted to reveal functional diversity of a bird community. Overall, even if the processes at the origin of the different facets of biodiversity are different, CAD reveals part of phylogenetic diversity and some extent of functional diversity.