Taxonomic sufficiency: The influence of taxonomic resolution on freshwater bioassessments using benthic macroinvertebrates

Changing the taxonomic scale of a biotic-assemblage dataset influences our ability to detect ecological patterns. In bioassessments, a test-site's biological community is compared against a benchmark to indicate ecosystem condition, but the taxonomic resolution needed to judge impairment reliably is the subject of much scientific debate. This paper re- views taxonomic sufficiency for freshwater benthic-macroinvertebrate bioassessments. Three main issues are discussed: (1) the ecological significance of different taxonomic aggregations; (2) trade-offs involving taxonomic detail and informa- tion content versus money, time, expertise, and data quality; and (3) sampling- and analytical-method-specific factors af- fecting taxonomic sufficiency. Although Species should be the default taxonomic level for bioassessments, taxonomic sufficiency is chiefly determined by a study's purpose, and pragmatism often dictates reduced detail. When a taxonomic- minimalism approach is necessary, a quantitative criterion for taxonomic sufficiency should be specified; this criterion should be based on an optimization of cost-benefit trade-offs associated with different taxonomic scales. Mixed-level ag- gregations, as well as morpho-species and ecological-trait classifications should be considered in this optimization process. Looking to the future, closer ties between taxonomists and bioassessment researchers would benefit both of their disci- plines. Such coordination would provide the autoecological information and better diagnostic tools (such as keys and mo- lecular methods) needed for biomonitoring, and better (and more widespread) biomonitoring would fuel taxonomy's resurgence.