We were comparing the diversity of moist and dry broadleaf forests as part of our Ecology project.
It was found that Shannon diversity index is greater for moist broadleaf forest and Simpson diversity index is greater for dry broadleaf forest. Can this happen or is it due to an error on our part?
We don't have prior experience in diversity index calculations or sampling. We followed the quadrant method for sampling.
That's correct. The Shannon-wiener index value increases with biodiversity. In contrast, the Simpson index measures the relative abundance of species, with a higher value indicating high dominance/low biodiversity. But you could just count species, which is a simple comparable metric between habitats :)
The values of the indices are abstract and difficult to compare, and situations such as the one reported can occur. The Shannon index may show higher biodiversity than Simpson's for a given area, because Shannon has a higher species richness weight.
Consider this:
Article What do we win 'confounding' species richness and evenness i...
The Simpson Diversity Index gives more weight to abundant species than to rare species. The presence of rare species in a population hardly changes the value of the diversity index, in contrast to the more sensitive Shannon index.
If Shannon index is higher than Simpson index value may be lesser. Simpson index (D) is similarity index while Simpson index of diversity (1-D) is actually diversity index . Shannon index shows uncertainty of capturing similar species during random sampling.
The Shannon-Weaver diversity index (commonly designated as H') is a measure for quantifying diversity and based on the number and abundance os species present. It varies betweeb 0 and S (the number of species present). The more the value is greater, the more the diversity of the stand is high. In other terms, high values of H' would be representative of more diverse communities with evenly distributed species. A community with one species would have an H' value 0. A simple case is a natural stand (higher diversity and complexity) versus a plantation stand (lower diversity).
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