Parameters to Assess Biological Diversity
- Species density: Species density is the number of species per unit area.
- Frequency distribution of species: If the species present in a biocoenosis are known, it is possible to determine their frequency distribution. From the quantitative composition of a biocoenosis, conclusions can be drawn as to its organisational structure: is the area dominated by one species with a high number of individuals, or do many species with similar numbers of individuals coexist in balance (evenness)?
- Rarity: The level of biodiversity in a specific area depends, inter alia, on the abundance of species occurring in that area. Islands or valleys, for instance, are frequently characterised by a high degree of endemism, i.e. species that occur only in a restricted habitat. When comparing two areas, it is thus essential to analyse them not only in terms of species richness, but also with respect to the rarity of the species present. The ratio between area-specific endemics and more widespread species (e.g. cosmopolitans) is of major importance in this context.
- Diversity in terms of species relationships: The diversity of different phylogenetic (i.e. pertaining to evolutionary history) lines of descent can be determined above the species level, e.g. at the family level. The more evolutionary lines diverge, the higher the degree of diversity in the investigation area. Another possibility to assess diversity in terms of species relationships is to determine the genetic variability between or within populations of one species.
- Proportion of endangered species: The number of endangered species in a particular area is used as a parameter to decide on protective measures to be taken.
- Functional diversity and ecosystem services: The species that occur in an area vary in terms of their significance for ecosystem services. The interactions between the occurring species, e.g. predator-prey relationships, pollination of plants, or competitive behaviour, may have an impact on ecosystem services.
- Non-indigenous species: The level of species diversity in a given area might be increased due to the presence of non-native species. The introduction of alien species by human activities may result in adverse effects on the existing ecosystems and even trigger biological invasions, including displacement of native species.
- Actual or potential value for human beings: If an area's biological diversity is considered to be of high actual or potential value for human beings, the quality of this area can be assessed in a different way to that of areas which are characterised by species richness, but are not of potential value.
Cf.:
Mutke, Jens / Barthlott, Wilhelm (2008): Biodiversität und ihre Veränderungen im Rahmen des Globalen Umweltwandels. (Biodiversity and its change in the context of global environmental change.) In: Lanzerath, Dirk / Mutke, Jens / Barthlott, Wilhelm / Baumgärtner, Stefan / Becker, Christian / Spranger, Tade M.: Biodiversität. (Biodiversity.) Ethik in den Biowissenschaften - Sachstandsberichte des DRZE, Bd.5. (Series: Ethics in the life sciences - DRZE expert reports, vol. 5). Freiburg i.B.: Alber.
Barthlott, Wilhelm / Mutke, Jens / Kier, Gerold (1999): Biodiversität - Globale Dimension und Verteilung genetischer Vielfalt. (Biodiversity - Global dimension and distribution of genetic diversity.) In: Niemitz, Carsten / Niemitz, Sigrun (ed.): Genforschung und Gentechnik. Ängste und Hoffnungen. Heidelberg: Springer, 55-71.