Global estimation of animal diversity using automatic acoustic sensors

The estimation of biodiversity can be considered as one of the main challenges in modern biology. When dealing with ecology, evolutionary biology and conservation biology, there is an inescapable need to describe the composition and dynamics of biological diversity (Magurran, 2004). In ecology, the concept of biological diversity is mainly species-oriented, even if other evolutionary units or traits can also be used. In this context, biodiversity potentially refers to all species encountered in a given area at a specified time, including every potential species from underground bacteria to giant trees. Therefore, biodiversity assessment can turn out to be a time-consuming and complex task, as it relies on species inventory that may involve very different taxonomic groups. Exhaustive approaches such as the all taxa biodiversity inventory (ATbI) programs aim at inventorying the whole biodiversity mainly in tropical habitats (Gewin, 2002), but these programs are highly sensitive to the logistic and time-constraints of most inventory studies. An alternative to these approaches is to focus on one or a few taxa and consider them as biodiversity indicators (Pearson, 1994), but the choice of representative taxa is not trivial (Lawton et al., 1998). In addition, it is well known that patterns of species diversity for different taxa are sensitive to the observation scale. More precisely, there is a general congruence for species diversity between different taxa at a large area scale (more than 1km 2) but not at a fine scale (less than 1km 2 , Weaver, 1995). This renders difficult the definition of an indicator taxon or even of several indicator taxa supposedly representative of the diversity in other forms of organisms (Ricketts 100 Biodiversity et al., 1999). Irrespective of the taxonomic breadth of any biodiversity assessment, the estimation of species biodiversity relies on inventories and species examination by one or several taxonomic experts that can be supported with genetic barcoding techniques (see chapter II, 3). Sampling in the field and identification in museum collections can require a considerable effort when the objective is to sample a large region for a long time period. To improve the rate of specimen collection, non-specialist taxonomic workers – or para-taxonomists – can separate morpho-species instead of identifying valid species. This solution is advocated by the rapid biodiversity assessment (RbA) programs that have been especially developed for the rapid exploration of biodiversity in tropical habitats Biodiversity assessment is often restricted to species richness, i.e. to the counting …