The value of RTUs and parataxonomy versus taxonomic species

Parataxonomy and the sorting of specimens to recognisable taxonomic units (RTUs) are common approaches to invertebrate biodiversity studies worldwide. However, there is an urgent need to assess and validate the use of RTUs as opposed to taxonomic species. Beetle (Coleoptera) assemblages were sampled from native and willow dominated riparian zones in the Hunua Ranges, Auckland. Beetles were sorted to RTUs by a parataxonomist, and then identified by a specialist Coleopterist. A comparison of the unverified (RTU) dataset with the verified (taxonomic species) dataset showed an overall 5.6% error rate, with seven more taxonomic species being identified than assigned to RTUs. RTU accuracy was problematic for several families, including Staphylinidae, Cryptophagidae and Latridiidae. However, in terms of ecological interpretation, both datasets gave almost identical results. Ranking of sites by species/RTU richness and the composition of the beetle fauna identified the same trends. Despite these results, we suggest that the RTU approach is overrated because of the loss in biological information associated with the RTU approach. We suggest the use of RTUs offers considerably less than a taxonomic species approach for invertebrate conservation in New Zealand, particularly in the long-term.