ecology Ecology () is the natural science of the relationships among living organisms and their Natural environment, environment. Ecology considers organisms at the individual, population, community (ecology), community, ecosystem, and biosphere lev ...

the relative abundance distribution (RAD) or

species abundance In ecology, local abundance is the relative representation of a species in a particular ecosystem. It is usually measured as the number of individuals found per sample. The ratio of abundance of one species to one or multiple other species livin ...

distribution 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. When plotted as a histogram of number (or percent) of species on the y-axis vs. abundance on an arithmetic x-axis, the classic hyperbolic J-curve or hollow curve is produced, indicating a few very abundant species and many rare species.McGill BJ, Etienne RS, Gray JS, Alonso D, Anderson MJ, Benecha HK, Dornelas M, Enquist BJ, Green JL, He F, Hurlbert AH. et al. 1999. ''Species abundance distributions: moving beyond single prediction theories to integration within an ecological framework. ''. Ecology Letters (2007): 10:995-1015. The SAD is central prediction of the Unified neutral theory of biodiversity. Starting in the 1970s and running unabated to the present day, mechanistic models (models attempting to explain the causes of the hollow curve SAD) and alternative interpretations and extensions of prior theories have proliferated to an extraordinary degree.McGill BJ, Etienne RS, Gray JS, Alonso D, Anderson MJ, Benecha HK, Dornelas M, Enquist BJ, Green JL, He F, Hurlbert AH. et al. 1999. ''Species abundance distributions: moving beyond single prediction theories to integration within an ecological framework. ''. Ecology Letters (2007): 10:995-1015. The graphs obtained in this manner are typically fitted to a Zipf–Mandelbrot law, the exponent of which serves as an index of

biodiversity Biodiversity is the variability of life, life on Earth. It can be measured on various levels. There is for example genetic variability, species diversity, ecosystem diversity and Phylogenetics, phylogenetic diversity. Diversity is not distribut ...

in the ecosystem under study.

Notes and references

Ecological metrics {{ecology-stub