Under the influence of inoculating organism in the soil can relative abundance exceeds while diversity indexes like shannon, simpson are low
Diversity index value is the quantification of diversity of whole community. But relative abundance is the relative availability of a species of that community.
Example - if there are only 3 species in a community of a large area, diversity value should be very less. But relative availability of one species among those 3 may be very high.
Relative abundance of the individual species is included in both Shannon and Simpson index. Those indices decrease when relative abundances of single species are particularly high, i.e., when there are few species in general or when relative abundances are unevenly distributed.
E.g., Simpsons D is given as
D = 1/(SUM(pi²))
Here, pi is the relative abundance of species i.
When all individuals of your sample belong to just one species, D will be 1. If there are two species, each accounting for 50% of the individuals, D will be 2. However, if you have two species and one of them accounts for 99% of the individuals, D will be barely larger than 1, because that one species dominates in the sample.
So this is exactly what those indices do: They indicate a low diversity if a few species are very dominant and a high diversity, if there are many species with only small individual abundances.
Some good explanations with examples can be found here:
http://www.tiem.utk.edu/~gross/bioed/bealsmodules/simpsonDI.html
To answer your own question, perhaps you could do a little experimentation. Assume that you have a population of 100 individuals of 10 species (A, B, C, D, E, F, G, H, I and J .
At one extreme you could try having 91 individuals of species A and just 1 individual of species B to J. This would be the least diverse and species A would have the greatest relative abundance.
Then try having all 10 species each with 10 individuals; this is the most diverse and all species have equal relative abundance.
You now have results for the two extremes, so why not try all sorts of other mixtures of the 10 species? For example, try 50 of A, 25 of B, 12 of C, 7 of D and 1 each of E to J. In such a hypothetical community, you can experiment with a number of different relative abundances and see how they influence the diversity indices which you have chosen.
Yes. It's possible to have a high relative abundance and low diversity indices. The illustrations given above by Michael Usher clearly explains it.
Diversity indices included Shannon, Simpson, Pielou take the proportion of the number of species and relative abundance at the same time. When the proportion of diversity is low, we have a high abundance and vice versa that means that the relative abundance is linked to the dominance of species and not the diversity.
Abundance is related to dominance but emphasizes on the relative proportions of different species in a community. The diversity index like Shanon-Weiner diversity index combines two components of diversity: (1) number of species and (2) evenness of allotment of individuals among the species. Usually, the Shanon-Weiner diversity index value increases with increase in the number of species and with a more even distribution among species.
Diversity indices e.g. Shannon wiener index depends on abundance and Simpson index depends on relative abundance. Both may positively or negatively differ correlated to species richness or other parameters involved in the community calculations like evenness index i.e. distribution of specimens of each species in the ecosystem.
Dear Chandandeep Kaur ,
Species diversity is not only measured by the number of species present within a biological community but when measuring the species diversity two factors which are considered known as species richness, and relative abundance.
Species richness is defined as the number of species in a particular area, and species abundance defined as the number of individual per species. Maybe two communities equally rich in species, but they are different in relative abundance.
Yes Chandandeep. The relative abundances of species in communities can affect the diversity indices of such communities. The reason is that diversity not only takes into consideration the species richness (the number of species) of a community but also the evenness in the distribution of the individuals that make up that community among the various species present. For example, let's consider two communities ( A and B) with five species and 100 individuals present in each of them. Assuming that the 100 individuals in Community A are distributed equally among the five species (i.e. 20, 20, 20, 20, 20) while a particular species in Community B accounts for a greater percentage of the individuals present (e.g. 70, 10, 10, 5, 3, 2), the diversity index for community A will be higher than that of Community B because of the very high relative abundance (or dominance) of the one species accounting for 70% of the total population in Community B.
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