Species evenness
Encyclopedia
Species evenness refers to how close in numbers each species in an environment are. Mathematically it is defined as a diversity index
, a measure of biodiversity
which quantifies how equal the community is numerically. So if there are 40 foxes, and 1000 dogs, the community is not very even. But if there are 40 foxes and 42 dogs, the community is quite even. The evenness of a community can be represented by Pielou
's evenness index:
Where
is the number derived from the Shannon diversity index
and
is the maximum value of 
, equal to:
E is constrained between 0 and 1. The less variation in communities between the species, the higher E is.
Other indices have been proposed by authors where
eg. Hurlburt's evenness index.
S is the total number of species.
Diversity index
A diversity index is a statistic which is intended to measure the local members of a set consisting of various types of objects. Diversity indices can be used in many fields of study to assess the diversity of any population in which each member belongs to a unique group, type or species...
, a measure of biodiversity
Biodiversity
Biodiversity is the degree of variation of life forms within a given ecosystem, biome, or an entire planet. Biodiversity is a measure of the health of ecosystems. Biodiversity is in part a function of climate. In terrestrial habitats, tropical regions are typically rich whereas polar regions...
which quantifies how equal the community is numerically. So if there are 40 foxes, and 1000 dogs, the community is not very even. But if there are 40 foxes and 42 dogs, the community is quite even. The evenness of a community can be represented by Pielou
E. C. Pielou
Evelyn Chrystalla Pielou is a statistical ecologist. She began her career as a researcher for the Canadian Department of Forestry and the Canadian Department of Agriculture...
's evenness index:
Where
is the number derived from the Shannon diversity indexShannon index
The Shannon index, sometimes referred to as the Shannon-Wiener Index or the Shannon-Weaver Index, is one of several diversity indices used to measure diversity in categorical data. It is simply the Information entropy of the distribution, treating species as symbols and their relative population...
and
is the maximum value of , equal to:E is constrained between 0 and 1. The less variation in communities between the species, the higher E is.
Other indices have been proposed by authors where
eg. Hurlburt's evenness index.S is the total number of species.
Weblinks
- C. P. H. Mulder, E. Bazeley-White, P. G. Dimitrakopoulos, A. Hector, M. Scherer-Lorenzen and B. Schmid: Species evenness and productivity in experimental plant communities. Oikos, 2004, no. 107. pp. 50–63 (PDF-Datei; 275 kB).