Original paper

Effects of taxonomic and numeric resolution on the ability to detect ecological patterns at a local scale using stream macroinvertebrates

Melo, Adriano S.


The increasing demand for methods of rapid stream bioassessment has stimulated the evaluation of data simplification. In particular, these studies have assessed how much power is lost when species/morphospecies identification is replaced by family identifications or use of EPT (Ephemeroptera, Plecoptera and Trichoptera) taxa only. A second simplifying factor commonly evaluated is the use of presence/absence data instead of density. These simplifications have provided valid results in most cases where differences among groups are large, particularly in studies comparing impacted vs. non-impacted stream sites and ecological studies involving large spatial scales. Here I evaluate whether data simplification, both in terms of taxonomic (families, morphospecies of EPT) and numeric (presence/absence) resolutions, is valid for ecological studies done at local scales, where differences among groups are subtle. Datasets used are derived from a five-year study of five stream sites situated in a catchment in southeast Brazil. Streams were sampled twice a year, in the rainy (summer) and dry (winter) seasons. I used Analysis of Similarity (ANOSIM) to evaluate if differences i) among stream sites and ii) between seasons within a stream site, revealed by using the full data set (morphospecies, quantitative data), were also detected when using the simplified datasets. The effect of taxonomic resolution was not significant; the two simplified levels of this factor (morphospecies of EPT, families) were able to recover the same groups revealed by the full dataset. However, the use of presence/absence data had a strong negative effect on the ability to distinguish groups, particularly when differences were small (between seasons within a stream site). The success in recovering groups using simplified taxonomic data agrees with previous evaluations done using datasets from applied fields and those from ecological studies involving large spatial scales. However, in contrast to results observed in applied and large-scale studies, use of simplified data quantification in local datasets resulted in significant loss of information. I suggest that the use of family identifications or morphospecies of EPT are reliable alternatives to the use of species/morphospecies in ecological studies at a local scale.


streamaquatic insectsbenthic invertebratesmorphospeciesdata quantificationbiological monitoring