Ambiguous taxa: effects on the characterization and interpretation of invertebrate assemblages

Abstract

Damaged and immature specimens often result in macroinvertebrate data that contain ambiguous parent-child pairs (i.e., abundances associated with multiple related levels of the taxonomic hierarchy such as Baetis pluto and the associated ambiguous parent Baetis sp.). The choice of method used to resolve ambiguous parent-child pairs may have a very large effect on the characterization of invertebrate assemblages and the interpretation of responses to environmental change because very large proportions of taxa richness (73-78%) and abundance (79-91%) can be associated with ambiguous parents. To address this issue, we examined 16 variations of 4 basic methods for resolving ambiguous taxa: RPKC (remove parent, keep child), MCWP (merge child with parent), RPMC (remove parent or merge child with parent depending on their abundances), and DPAC (distribute parents among children). The choice of method strongly affected assemblage structure, assemblage characteristics (e.g., metrics), and the ability to detect responses along environmental (urbanization) gradients. All methods except MCWP produced acceptable results when used consistently within a study. However, the assemblage characteristics (e.g., values of assemblage metrics) differed widely depending on the method used, and data should not be combined unless the methods used to resolve ambiguous taxa are well documented and are known to be comparable. The suitability of the methods was evaluated and compared on the basis of 13 criteria that considered conservation of taxa richness and abundance, consistency among samples, methods, and studies, and effects on the interpretation of the data. Methods RPMC and DPAC had the highest suitability scores regardless of whether ambiguous taxa were resolved for each sample separately or for a group of samples. Method MCWP gave consistently poor results. Methods MCWP and DPAC approximate the use of familylevel identifications and operational taxonomic units (OTU), respectively. Our results suggest that restricting identifications to the family level is not a good method of resolving ambiguous taxa, whereas generating OTUs works well provided that documentation issues are addressed.

Effects of streamflow reductions on aquatic macroinvertebrates: linking groundwater withdrawals and assemblage response in southern New Jersey streams, USA

“…Aquatic-macroinvertebrate data processing (i.e. censoring and resolving taxonomic ambiguities) was accomplished with the Invertebrate Data Analysis System (IDAS) (Cuffney 2003, Cuffney et al 2007. Ambiguities in the taxonomic hierarchy (i.e.…”

“…organisms that are not completely identified because of small size, incomplete development, damage, or poor preservation) were typically resolved by distributing the abundance of the ambiguous parents among their children in accordance with the relative abundance of each child (Cuffney 2003). This approach, which represents a compromise between removing redundant taxonomic information and conserving quantitative information on taxa richness and abundance (Taylor 1997), is one of the methods suggested by Cuffney et al (2007). After taxonomic data processing, the IDAS program was used to calculate a suite of macroinvertebrate-assemblage metrics and diversity measures, many of which are commonly used in stream bioassessment (Barbour et al 1999).…”

Before and after the deluge: rain-on-snow flooding effects on aquatic invertebrate communities of small streams in the Sierra Nevada, California

“…In addition, crew members did visual collections during which they walked the stream reach and sampled habitats and substrate types that might have been missed or under-sampled by the other collection techniques (NCDENR 2006). We followed guidelines in Cuffney et al (2007) to develop operational taxonomic units (OTUs) for each database to exclude ambiguous taxa from the analyses and to include only distinct/unique taxa. Because of taxonomic ambiguities in the long-term data, genuslevel OTUs were generally most appropriate, although there were some exceptions.…”

Influences of forest harvest and environmental gradients on aquatic invertebrate communities of seasonal ponds

“…Higher taxonomic resolution was not possible due to the large collections, an abundance of immature specimens and undescribed species, and because a number of groups await revision. In cases in which taxonomic ambiguity (sensu Cuffney et al, 2007) was a factor, we used the ''distribute parents among children'' approach on a per sample basis, except where specific knowledge allowed more targeted allocation of ambiguous taxa.…”