Dear Sileesh,

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 visualizespecies richness and species evenness. It overcomes the shortcomings of biodiversity indices that cannot display the relative role different variables played in their calculation.

A rank abundance curve

The curve is a 2D chart with relative abundance on the Y-axis and the abundance rank on the X-axis.

·         X-axis: The abundance rank. The most abundant species is given rank 1, the second most abundant is 2 and so on.

·         Y-axis: The relative abundance. Usually measured on a log scale, this is a measure of a species abundance (e.g., the number of individuals) relative to the abundance of other species

The rank abundance curve visually depicts both species richness and species evenness. Species richness can be viewed as the number of different species on the chart i.e., how many species were ranked. 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.

Relative species abundance is a component of biodiversity and refers to how common or rare a species is relative to other species in a defined location or community. Relative abundance is the percent composition of an organism of a particular kind relative to the total number of organisms in the area. Relative species abundances tend to conform to specific patterns that are among the best-known and most-studied patterns in macro ecology.

 Regards,

Prem Baboo

https://www.google.co.in/url?sa=t&rct=j&q=&esrc=s&source=web&cd=10&cad=rja&uact=8&ved=0ahUKEwjD1JbizeHNAhUDs48KHUGfCtQQtwIIVzAJ&url=https%3A%2F%2Fwww.youtube.com%2Fwatch%3Fv%3Dbk7oIVasf7A&usg=AFQjCNFZt2BKX9fc88EFL6pvrVG7k2nfNg

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1. Steep gradient referred to low evenness (I have 24 specimen for 5 different species in a location as 10+5+7+1+1=24)

2. Shallow gradient referred to high evenness (25 specimen for 5 different species in a location as 5+5+5+5+5=25, means abundance of different species are similar or almost similar compare to 1)

Here, number 1 has low evenness and low richness (24

Rank abundance curve is indicating species richness and relative abundance. Slope of the curve represents species evenness....steepness of curve shows low evenness while continuing steepness shows high eveness