Rank abundance curve

A rank abundance curve or Whittaker plot is a chart used by ecologists to display relative species abundance, a component of biodiversity.

It overcomes the shortcomings of biodiversity indices that cannot display the relative role different variables played in their calculation.

Species evenness is reflected in the slope of the line that fits the graph (assuming a linear, i.e. logarithmic series, relationship).

A steep gradient indicates low evenness as the high-ranking species have much higher abundances than the low-ranking species.

A shallow gradient indicates high evenness as the abundances of different species are similar.