Species extinction is only the last step of a long process of ecosystem degradation. The measuring of this decrease and increase of abundance on a core set of species is a most promising indicator of biodiversity loss. Further, species abundance is a sensitive measure. Nevertheless, next to species also other quality variables are possible, e.g. at the ecosystem or genetic level, but these are less advantageous. It is not possible to measure all biodiversity.
Arbitrary choices are inevitable.
Based on the above considerations, the Natural Capital Index framework has been developed. Ecosystem quality is a function of a core set of quality variables.