Indicator value

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This term is ambiguous: Ellenberg's indicator values are simple ordinal classes of organisms (initially plants) with a similar realized ecological niche along a gradient. The latest edition of Ellenberg's indicator values contain values on a 9 point scale for soil acidity, productivity/nutrients, soil humidity, continentality, soil salt content and light. Indicator values also exist in Landolt's Flora of Switzerland and some other floras. A substantial advance on a comparable scale to place a local flora on gradients are the climatic profiles of the french SOPHY online database. Ellenberg's indicator values have a long tradition in interpretation and understanding of plant communities and their evolution. Dufrêne & Legendre's indicator values are a measure of alliance of a particular taxon to a group of (in general) multi-species-samples. Created by Dufrêne, M. and P. Legendre the IndVal Method is used to identify the indicator value of a specific species. Relative abundance is compared to frequency in order to find a percentile that gives the best idea of this species as an indicator. There are many uses for IndVal, one being the calculating of IndVal for lichens which gives a percentage of an indicative species of lichen that portrays the amount of air pollution. Indicative species can be used in ecology in order to see specific biotic and abiotic factors on the environment as they effect the species in a specific manner.

[edit] Calculating the Indicator Value

To calculate the indicator value of a given species, the equation IndVal_ij = A_ij * B_ij * 100 is used.

A_ij = mean amount of i in j.
i = The average amount of the species in the site (abundance)
j = The amount of sites.
Hence A_ij = Nindividuals_ij/Nindividuals_i.
B_ij equals the same thing except that i is the frequency of occurrence, rather than the abundance, hence B_ij = Nsites_ij/NSites_i.
Finally, IndVal_ij = A_ij * B_ij * 100