Taxonomic sufficiency in ecological studies of terrestrial invertebrates

The concept of taxonomic sufficiency (identifying organisms only to a level of taxonomic resolution sufficient to satisfy the objectives of a study) has received little attention in ecological studies of terrestrial invertebrate assemblages. Here we critically evaluate three approaches to taxonomic sufficiency: the use of morphospecies, genera and functional groups. The objective was to compare estimates of richness (α diversity) and turnover (β diversity) of ant assemblages generated by these data with estimates produced using data for ant species. Ground-active ants were sampled using pitfall trapping within three habitat types: a eucalypt plantation, woodland regrowth patches and the surrounding grassland at a study site in the upper Hunter Valley, New South Wales. Comparisons of assemblage richness and turnover among taxonomic data sets and habitats and after different data transformations used univariate (simple correlation and ANOVA) and multivariate (Mantel tests, ANOSIM and SSHMDS) techniques. Our study found: (i) morphospecies and genus richness was highly correlated with species richness over the study area; (ii) ordination scatterplots using species, morphospecies and genus data revealed similar patterns of site separation for the three habitats; (iii) the results were very similar using untransformed, log transformed and binary data; (iv) functional group ordinations separated all three habitat types for untransformed abundance data; and (v) estimates of species turnover were highly correlated with estimates of morphospecies and genus turnover. These results are discussed in relation to future monitoring of ant community structure.