Alpha diversity

Alpha diversity
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Alpha_diversity".

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. This can be measured by counting the number of taxa (distinct groups of organisms) within the ecosystem (eg. families, genera, species). 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.

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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.

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.
   * 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. 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.
Gamma diversity – taxonomic diversity of a region with several ecosystems.
Phylogenetic diversity – or 'Omega diversity'. 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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