There are many more rare species than common ones in ecological assemblages. These data, representing the numbers of individuals in the 81 species making up a 25 year time series of estuarine fish in the UK's Bristol Channel, were collected by PA Henderson. (a) The data plotted on an arithmetic scale to emphasize the handful of exceptionally abundant species; (b) the same data, with the abundance now plotted on a logarithmic scale (this type of graph is usually called a rank abundance plot); and (c) a histogram showing the frequency of species in logarithmic abundance classes. The plot in (c), which was introduced by Frank Preston, illustrates the log normal pattern of diversity often seen in ecological assemblages. These different methods of plotting species abundance data highlight contrasting aspects of the assemblage, but they all underline the universal pattern of a few abundant and many rare species.