species evenness
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Species evenness refers to how close in numbers each species in an environment is. Mathematically it is defined as a
diversity index A diversity index is a quantitative measure that reflects how many different types (such as species) there are in a dataset (a community), and that can simultaneously take into account the phylogenetic relations among the individuals distributed a ...
, a
measure of biodiversity Conservation biologists have designed a variety of objective means to measure biodiversity empirically. Each measure of biodiversity relates to a particular use of the data. For practical conservationists, measurements should include . For othe ...
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: :J'= Where H^\prime is the number derived from the Shannon diversity index and H_\max^\prime is the maximum possible value of H^\prime (if every species was equally likely), equal to: :H^\prime_\max = - \sum_^S \ln = \ln S. ''J is constrained between 0 and 1. The less evenness in communities between the species (and the presence of a dominant species), the lower ''J is. And vice versa. Other indices have been proposed by authors where H_\min^\prime > 0 e.g. Hurlburt's evenness index. S is the total number of species. Species evenness requires ecologists to know the abundance of species relative to other species in a given community. The methods used to measure abundance are area-based counts, distance methods, and mark-recapture studies. Area-based counts are used for measuring the abundance of immobile organisms and it involves measuring the number of organisms in a series of quadrants to get an estimate of the total population. In distance methods, the distance of individuals from a random point is collected and converted into the number of individuals per unit of area. Mark-recapture methods are useful for estimating the abundance of mobile organisms. Ecologists capture a subset of the population that they mark and release. The marked individuals are given time to move through the population, and then individuals are recaptured a second time. The proportion of marked individuals found in the recapture is used to estimate the total population size.


See also

*
Biodiversity Biodiversity or biological diversity is the variety and variability of life on Earth. Biodiversity is a measure of variation at the genetic (''genetic variability''), species (''species diversity''), and ecosystem (''ecosystem diversity'') l ...


External links

* * Measurement of biodiversity {{Ecology-stub