Higher taxa in biodiversity studies: patterns from eastern Pacific marine molluscs

Several recent studies have proposed the use of higher taxa as a proxy for species-level biodiversity patterns. Here this premise is evaluated by using a large database of benthic marine molluscs from the eastern Pacific. In this assemblage, diversity patterns at the genus and family level are significantly correlated with those at the species level. However, the choice of taxonomic rank depends on the resolution required to address a given problem. Although familial data are very robust to sampling and adequately reflect the general species-level patterns (for example, the presence and sign of diversity gradients), they cannot adequately resolve regional variations such as stepped diversity trends. Genera are useful even at regional scales, but species-frequency distributions within higher taxa vary with diversity (and biogeography). Hence, for regional studies, calibration based on a few well-sampled local assemblages is recommended to increase the effectiveness of genera as proxies for species-level patterns. Information contained within the taxonomic hierarchy can also provide insights into other macroecological patterns that are not evident from a simple tabulation of species, such as estimates of the latitudinal deployment of biodisparity.