Beta diversity
The beta diversity (ger .: diversity, Germanized to diversity) is a measure of the difference in diversity between different spatially distributed in a landscape communities. The term is defined in a theory of the American ecologist Robert H. Whittaker (Whittaker 1960) and is only used in the context of the application of his theory. The main measure of ecological diversity is the number of species.
Definition and measurement
Whittaker first looks at the local diversity at a certain point (a partial habitat, a sample area, etc.), which he calls alpha diversity. At a higher level, the increase in diversity depends primarily on how different the individual points are from one another. This is "also between habitat " or " species turnover " ( mode change) called. The fewer species the habitats have in common (given alpha diversity), the greater the beta diversity. If all local communities are identical at all local points, beta diversity is minimal. If they don't have a single species in common, it becomes maximal. Beta diversity is particularly relevant when considering the effects of variations in living conditions (e.g. habitat gradients such as temperature or humidity gradients).
The introduction of beta diversity as a measure is primarily intended to distinguish between local and regional effects. A community can consist of a great number of species locally, i.e. have high alpha diversity, but be regional but uniform, so that the same species-rich community occurs everywhere in the same composition. In contrast to this, the community in all examined locations may be rather species-poor (low alpha diversity), but regionally extremely different. High alpha and high beta diversity do not have to be related to one another.
To determine the beta diversity, one can determine the ratio between the total number of species in all individual measurements and the mean number of species in these measurements. Special assumptions about distribution patterns are not necessary.
If one plots the individual measurements, sorted according to their number of species, from the species-poorest to the most species-rich, in a diagram, whereby one does not represent the absolute number of species of each measurement, but only the species that have been added by a new measurement / a new sub-habitat (a so-called species-rank diagram), the beta diversity is shown in the slope of the resulting curve. The curve asymptotically tends towards a saturation level if the number of species no longer increases when further samples are added, i.e. H. the regional species pool is fully recorded. In other cases, the measured value for beta diversity still depends on the recording effort and should only be interpreted with caution.
See also
literature
- Whittaker, RH (1960) Vegetation of the Siskiyou Mountains, Oregon and California. Ecological Monographs 30, 279-338.
- Whittaker, RH (1972) Evolution and Measurement of Species Diversity. Taxon 21, 213-251.
- Whittaker, RH (1977) Evolution of species diversity in land communities. Evolutionary biology 10 (editors MK Hecht, WC Steere and B. Wallace), 250-268. Plenum Press (New York).