Alpha diversity - Citizendia

Alpha diversity (α-diversity) is the biodiversity within a particular area, community or ecosystem, and is usually expressed as the Species richness of the area. Biodiversity is the variation of Life forms within a given Ecosystem, Biome or for the entire Earth. In biological terms a community is a group of interacting Organisms sharing an environment. An ecosystem is a natural unit consisting of all plants animals and micro-organisms( Biotic factors in an area functioning together with all of the non-living physical ( Species richness is the number of species in a given area It is represented in Equation form as S This can be measured by counting the number of taxa (distinct groups of organisms) within the ecosystem (eg. A taxon (plural taxa) or taxonomic unit, is a name designating an organism or a group of Organisms In Biological nomenclature according to families, genera, species). Family denotes a group of People affiliated by consanguinity affinity or co-residence A genus (plural genera from Γένος Latin genus "descent family type gender" is a low-level Taxonomic In Biology, a species is one of the basic units of Biological classification and a Taxonomic rank. However, such estimates of species richness are strongly influenced by sample size, so a number of statistical techniques can be used to correct for sample size to get comparable values.

1 Simpson's Diversity Index
2 Shannon index
3 Fisher's Alpha
4 Rarefaction
5 Other measures of diversity
6 External links
7 References

Simpson's Diversity Index

$D=\frac{\sum_{i=1}^S n_i(n_i-1)}{N(N-1)}$

Where S is the number of species, N is the total percentage cover or total number of organisms and n is the percentage cover of a species or number of organisms of a species. Simpson's diversity index (also known as Species diversity index is one of a number of Diversity indices, used to measure of diversity

Shannon index

$H^\prime = -\sum_{i=1}^S p_i \ln p_i$

where

   * ni The number of individuals in each species; the abundance of each species. The Shannon index, also known as the Shannon-Weaver Index and sometimes referred to as the Shannon-Wiener Index) H^{\prime} is one of several diversity 
   * S The number of species.  Also called species richness. 
   * N The total number of all individuals
   * pi The relative abundance of each species, calculated as the proportion of individuals of a given species 
     to the total number of individuals in the community:

Fisher's Alpha

Rarefaction

Rarefaction takes hypothetical subsamples of n organisms from the more-sampled region, and calculates the average number of species in such subsamples. In Ecology, rarefaction is a technique to to standardize and compare Species richness computed from samples of different sizes This average can be compared to the number of species actually found in the less-sampled region

Other measures of diversity

Alternative ways to measure biodiversity include^[1]. :

Beta diversity – species diversity between ecosystems; this involves comparing the number of taxa that are unique to each of the ecosystems. Beta diversity (β-diversity is a measure of Biodiversity which works by comparing the species diversity between Ecosystems or along Environmental gradients
Gamma diversity – taxonomic diversity of a region with several ecosystems. Gamma diversity (γ-diversity is a measure of Biodiversity. It refers to the total biodiversity over a large area or region
Phylogenetic diversity – or 'Omega diversity'. Phylogenetic diversity is a measure of biodiversity which incorporates taxonomic difference between species The differences or diversity between taxa
Global diversity – overall biodiversity of Earth.

Diversity may not be congruent at all taxonomic levels and diversity patterns may vary depending on the type of diversity measured, as seen in the example to the left.

External links

An explanation of many specific biodiversity terms using illustrations http://www.uwsp.edu/geo/faculty/heywood/geog358/Diversity/Biodiversity.htm

References

^ Whittaker, R. H. , 1972. Evolution and measurement of species diversity. Taxon 21: 213–251.

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