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 = Nindividuals_ij/Nindividuals_i
ij = The average amount of the species i in zone j (abundance)
i = Mean values for i in all zones

B_ij = Nsites_ij/NSites_i.
ij = Number of sites in zone j where species i is present (frequency)
i = Number of sites in zone j
Finally, IndVal_ij = A_ij * B_ij * 100

[edit] Explanation

This compares the fidality, distribution, and abundance of a specific species to all the other zones and samples with in a zone. This is where zones are specific to the factor being tested. For instance Zone 1 is a heavy pollution zone, Zone 2 medium pollution, and Zone 3 light pollution if one is to set up zones to obtain an indicator value of lichen abundance and fidelity in relation to pollution. 100 is mulitplied to the end result to get a percentage while a percentage of 25% or heigher is usually considered indicative of the specific zone. Student t tests and other statistical test can further establish conclusive results.