Evans O. Ochiaga Cang Hui Theoretical Ecology Group, Department of Mathematical Sciences, Stellenbosch University, Matieland 7602, and African Institute for Mathematical Sciences, Muizenberg 7945, South Africa Computational Ecology and Software ISSN 2220-721X http://www.iaees.org/publications/journals/ces/online-version.asp 2015 5 4 340 353 International Academy of Ecology and Environmental Sciences Hong Kong 25 July 2015 3 August 2015 1 December 2015 maximum entropy lognormal neutral theory proportionate effect biodiversity Species abundance distribution (SAD) is one of the most important metrics in community ecology. SAD curves take a hollow or hyperbolic shape in a histogram plot with many rare species and only a few common species. In general, the shape of SAD is largely log-normally distributed, although the mechanism behind this particular SAD shape still remains elusive. Here, we aim to review four major parametric forms of SAD and three contending mechanisms that could potentially explain this highly skewed form of SAD. The parametric forms reviewed here include log series, negative binomial, lognormal and geometric distributions. The mechanisms reviewed here include the maximum entropy theory of ecology, neutral theory and the theory of proportionate effect. DOI 10.0000/issn-2220-721x-compuecol-2015-v5-0025 http://www.iaees.org/publications/journals/ces/articles/2015-5(4)/forms-and-genesis-of-species-abundance-distributions.pdf