A rank abundance curve or Whittaker plot is a chart used by ecologists to display relative species abundance, a component of biodiversity. It can also be used to visualize species richness and species evenness. It overcomes the shortcomings of biodiversity indices that cannot display the relative role different variables played in their calculation.
The curve is a 2D chart with relative abundance on the Y-axis and the abundance rank on the X-axis.
Ecological dominance is the degree to which one or several species have a major influence controlling the other species in their ecological community (because of their large size, population, productivity, or related factors) or make up more of the biomass. Both the composition and abundance of species within an ecosystem can be affected by the dominant species present.
In most of the world's ecosystems, biologists have repeatedly observed a rank-abundance curve in which ecosystems comprise a handful of incredibly abundant species, but more numerous, rarer species that are few in number. Danish botanist Christen C. Raunkiær described this phenomenon as his "law of frequency" in 1918, in which he recognized that in communities with a single species accounting for most of the biomass, species diversity was often lower.