Effects of Sequentially Removing Low-Abundance Taxon Records from Community Matrices on Aquatic Insect Community Evaluation in Mountain Streams

Low-abundance taxa are often filtered out of data sets before community analysis, which may remove information on both spatial community differences and associations between community composition and environmental gradients. We studied aquatic insect communities in mountain streams of the Hengduan Mountains, China, and sequentially removed low-abundance taxa from the lowest to the highest regional abundance. We compared community spatial heterogeneity, environmental and spatial associations, similarity between filtered and complete community matrices, and taxon-specific effects. Spatial turnover declined first, followed by abundance-based community dissimilarity. Associations of the community with environmental and spatial gradients were reorganized during removal, and compositional departure accelerated late in the sequence. The main effect dimension differed among taxa. Low abundance does not imply redundant ecological information: the uneven distribution of low-abundance taxon records contributes to estimated local distinctiveness and affects environmental and spatial associations as well as similarity to the complete community. Monitoring and community analyses in mountain streams should retain raw taxon records when possible, evaluate sensitivity to analytical filtering, and apply filtering rules suited to the study objective.