Comparison of Some Species Importance Values and Ordination Techniques Used to Analyse Benthic Invertebrate Communities

Abstract

As part of a study of benthic invertebrate communities some aspects of different ordinations were compared. Two ordination methods (the Bray and Curtis and a position vectors type) and two types of species importance values were compared. The importance values were: density times the square root of frequency (DFR) and oxygen consumption. Two questions were posed: did the two importance values used produce similar rankings of species by order of importance, and did the importance values affect resulting ordinations by different methods? 02-based importance values tended to emphasize the importance of large-sized but relatively low density species, whereas, the opposite effect was obtained by using DFI. Although the different importance values significantly changed the relative importance and subsequent ranking of the various invertebrate species, they had little effect on the ordinations by either method. Comparison of the ordination methods showed the methods agreed on what was the first or most important axis. Beyond the first axis the methods did not agree, and the comparisons revealed previously described weaknesses of the Bray and Curtis method.