Numerical Extrapolation of the Species Abundance Distribution Unveils the True Species Richness and the Hierarchical Structuring of a Partially Sampled Marine Gastropod Community in the Andaman Islands (India)

Even when it remains substantially incomplete, the partial inventory of a species assemblage can provide much more information than could be expected at first. This can be achieved by applying a rigorous numerical extrapolation procedure that fully extends the incomplete sampling in numerical terms and, thereby, provides reliable estimates regarding not only the number but also the distribution of abundances for the whole set of the undetected species. As a result, this makes available the full range of the Species Abundance Distribution of the yet partially sampled assemblage and, thus, allows to address a series of interesting issues regarding the process and pattern of the hierarchical structuring of species abundances within the studied assemblage of species. Moreover, the same kind of numerical extrapolation may be applied separately to each subset of species, within the whole assemblage, that may have relevant interest (taxonomic subgroups, feeding guilds, etc…). Thus, deconstructing the Species Abundance Distribution can provide further detailed insights into the functional organisation of the studied assemblage.

The mathematical and algorithmic basis for this extrapolating procedure has been developed recently, to be applied to the numerical extension of both the Species Accumulation Curve and the Species Abundance Distribution.

The wide potential interest of this new methodological approach, when having to deal with substantially incomplete inventories of species (which is doomed to become inevitable with increasingly species-rich assemblages), is illustrated by a detailed case study of a marine gastropod assemblage on rocky shore under tropical climate.