INFLUENCE OF SAMPLE QUANTIFICATION AND TAXONOMIC RESOLUTION ON THE ORDINATION OF MACROINVERTEBRATE COMMUNITIES FROM RUNNING WATERS IN VICTORIA, AUSTRALIA

The influence of sample quantification and taxonomic resolution on the ordination of macroinvertebrate communities from nine Victorian river s was examined by progressively reducing the degree of detail in the o riginal data (species level, quantitative). Five additional data sets were created that consisted of binary (presence or absence) data on sp ecies, quantitative or binary data on families, and quantitative data on PET (plecopteran, ephemeropteran and trichopteran) species or famil ies. Ordinations were performed with detrended correspondence analysis (DCA) and semi-strong hybrid multi-dimensional scaling (SSH). With bo th ordination techniques, the ordinations of each data set (including the original) revealed the same three underlying gradients. An altitud inal gradient consistently achieved the highest correlations with the ordinations (r = 0 . 71-0 . 93), followed by a substratum gradient (r = 0 . 50-0 . 88) and a combined pH and conductivity gradient (r = 0 . 47-0 . 76). Each of the five less-complete data sets thus provides an adequate degree of detail for ordination analysis and subsequent inter pretation of environmental gradients.