Dark diversity

Dark diversity is the set of species that are absent from a study site but present in the surrounding region and potentially able to inhabit particular ecological conditions.

[6] The existence of these phantom species means that routine measures of colonization and extinction at a site will always overestimate true rates because of "pseudo-turnover."

Similarly, dark diversity cannot be seen directly when only the sample is observed, but it is present if broader scale is considered, and its existence and properties can be estimated when proper data is available.

Thus, habitat specificity does not mean that all species in dark diversity can inhabit all localities within study sample, but there must be ecologically suitable parts.

Region size determines the likelihood of dispersal to the study site and selecting the appropriate scale depends on the research question.

The community completeness index can be used: This expresses the local diversity at the relative scale, filtering out the effect of the regional species pool.

For example, if completeness of plant diversity was studied at the European scale, it did not exhibit the latitudinal pattern seen with observed richness and species pool values.

Instead, high completeness was characteristic to regions with lower human impact, indicating that anthropogenic factors are among the most important local scale biodiversity determinants in Europe.

Common cowslip ( Primula veris ) is a frequent plant species in European grasslands. If the environmental conditions of a studied grassland patch are suitable, but the cowslip is missing from it, the plant belongs to the dark diversity for that given grassland.