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Biodiversity is commonly measured in terms of taxonomic richness of a geographic area over a time interval. In order to calculate biodiversity, species evenness, species richness, and species diversity are to be obtained first. Species evenness is the relative number of individuals of each species in a given area. [1]
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.
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.
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]
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.
The Bray–Curtis dissimilarity is bounded between 0 and 1, where 0 means the two sites have the same composition (that is they share all the species), and 1 means the two sites do not share any species. At sites with where BC is intermediate (e.g. BC = 0.5) this index differs from other commonly used indices. [3]
This type of dataset is typical in biodiversity studies. Observe how more than half the biodiversity (as measured by species count) is due to singletons. For real datasets, the species abundances are binned into logarithmic categories, usually using base 2, which gives bins of abundance 0–1, abundance 1–2, abundance 2–4, abundance 4–8, etc.