Indicator value

Indicator value is a term that has been used in ecology for two different indices. The older usage of the term refers to Ellenberg's indicator values, which are based on a simple ordinal classification of plants according to the position of their realized ecological niche along an environmental gradient. More recently, the term has also been used to refer to Dufrêne & Legendre's indicator value, which is a quantitative index that measures the statistical alliance of a species to any one of the classes in a classification of sites.
Ellenberg's Indicator Value.
Ellenberg's indicator values were the first model of bioindication proposed and applied to the flora of Central Europe, and they have a long tradition in interpretation and understanding of plant communities and their evolution. The latest edition of Ellenberg's indicator values applies a 9-point scale for each of seven gradients: <br><br>
R - reaction (soil or water acidity/pH) <br>
N - nitrogen (but really soil fertility or productivity, and not mineral nitrogen) <br>
F - soil humidity or moisture <br>
S - salt (soil salinity)<br>
K - climatic continentality<br>
L - light availability<br>
T - temperature <br><br> 
Indicator values have also been published for Switzerland, Great Britain, 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.
Indicator Value of Dufrêne and Legendre.
This indicator value is an integral part of the indicator value, which quantifies the fidelity and specificity of species in relation to groups of sites in a user-specified classification of sites, and tests for the statistical significance of the associations by permutation.
The indicator value of species "i" for class "j" is obtained with the equation 
Here