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If greater biodiversity value is associated with richness in a currency of expressible genes (or the characters of organisms for which they code), then when resources for sampling are limited, higher levels of biological organisation (or of the environmental factors affecting its distribution) will have to be employed for more practical surrogate measures (the term assemblages is used here for non-monophyletic groups of organisms, although it is debatable whether ecosystems, if defined in terms of processes, can be mapped and counted). Choosing a surrogacy level from this scale is a compromise between precision of the measure on the one hand, and availability of data and cost of data acquisition on the other (ref 4) (below):
Choosing surrogates to use in measuring biodiversity value
| Advantage:
precision as a measure of character diversity |
A scale of surrogacy for a value currency of character diversity | Advantage:
inexpensive surveys and units more inclusive of viability enhancing processes |
|
| low | ECOSYSTEM richness | high | |
| environmental surrogates |  |
climate class richness |  |
|
terrain class richness | |
|
|
substrate class richness | |
|
| environmental / assemblage
surrogates |
|
landscape class richness | |
|
habitat class richness | |
|
| assemblage surrogates | |
'community' class richness | |
|
vegetation class richness | |
|
| taxonomic surrogates | |
higher taxon richness | |
|
SPECIES / subspecies richness | |
|
|
taxonomic/phylogenetic subtree richness | |
|
| high | GENE / character richness (currency) | low |
A consequence of this approach to valuing biodiversity is that it provides one possible unified view of the traditional three levels at which biodiversity has been described. In effect it uses genetic diversity as a basis for valuing both species diversity (for their relative richness in different genes) and ecosystem diversity (for the relative richness in the different processes to which the genes ultimately contribute).
