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Species evenness is the relative number of individuals of each species in a given area. [1] Species richness [2] is the number of species present in a given area. Species diversity [3] is the relationship between species evenness and species richness. There are many ways to measure biodiversity within a given ecosystem.
The observed species richness is affected not only by the number of individuals but also by the heterogeneity of the sample. If individuals are drawn from different environmental conditions (or different habitats), the species richness of the resulting set can be expected to be higher than if all individuals are drawn from similar environments.
Relative species abundance is a component of biodiversity and is a measure of how common or rare a species is relative to other species in a defined location or community. [1] Relative abundance is the percent composition of an organism of a particular kind relative to the total number of organisms in the area.
SAD is a measurement of how common, or rare species are within an ecosystem. [5] This allows researchers to assess how different species are distributed throughout an ecosystem. SAD is one of the most basic measurements in ecology and is used very often, therefore many different methods of measurement and analysis have developed. [5]
Species richness, or biodiversity, increases from the poles to the tropics for a wide variety of terrestrial and marine organisms, often referred to as the latitudinal diversity gradient. [1] The latitudinal diversity gradient is one of the most widely recognized patterns in ecology. [1] It has been observed to varying degrees in Earth's past. [2]
The technique of rarefaction was developed in 1968 by Howard Sanders in a biodiversity assay of marine benthic ecosystems, as he sought a model for diversity that would allow him to compare species richness data among sets with different sample sizes; he developed rarefaction curves as a method to compare the shape of a curve rather than absolute numbers of species.
abundance class 1 1-2 2-4 4-8 8-16 species 5 0 1.5 1.5 1 The three species of abundance four thus appear, 1.5 in abundance class 2–4, and 1.5 in 4–8. The above method of analysis cannot account for species that are unsampled: that is, species sufficiently rare to have been recorded zero times.
Since the sum of the p i values equals 1 by definition, the denominator equals the weighted geometric mean of the p i values, with the p i values themselves being used as the weights (exponents in the equation). The term within the parentheses hence equals true diversity 1 D, and H' equals ln(1 D). [2] [4] [5]