Relative abundance distribution

In ecology the relative abundance distribution (RAD) or species abundance distribution (SAD) describes the relationship between the number of species observed in a field study as a function of their observed abundance. The SAD is one of ecology's oldest and most universal laws – every community shows a hollow curve or hyperbolic shape on a histogram with many rare species and just a few common species.

Source: Wikipedia — Relative abundance distribution (CC BY-SA 4.0)