A range of distributional techniques, also termed graphical or curvilinear plots, were used
to summarise the set of species counts for a single sample by a curve or histogram. The
purpose of graphical distributional representations is to extract information on patterns of
relative species abundances without reducing that information to a single summary
statistic, such as a diversity index.
Geographic abundance plots were used as a measure of community stress at the site
level and to assess differences in benthic community structure on different macrophyte
hosts. Species were combined in geometric abundance classes, i.e. the number of species
represented by only 1 individual in the sample (class 1), 2-3 individuals (class 2), 4-7
individuals (class 3), 8-15 individuals (class 4) etc. are illustrated in the graphs (cp. Gray
and Pearson 1982). If the biotic communities are not disturbed or impacted, it is assumed
that there are many rare species, and the geometric abundance curve will be smooth with
its mode well to the left (Clarke and Warwick 2001). On the other hand, if there is any
impact or disturbance, fewer rare and more abundant species are expected, so the higher
geometric abundance classes are more strongly represented, and the curve may become
irregular or jagged.
k-dominance curves are cumulative ranked abundances plotted against species rank
(Lambshead et al. 1983), the species being ranked in decreasing order of abundance.
Therefore, the most elevated curve will have the lowest diversity.