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Ecologists and environmental scientists use several different indices to quantify biodiversity. One example is species richness, which is the total number of different organisms present – it doesn’t take into account the proportion and distribution of different subspecies within an area. Another example is Simpson’s Index, which takes into account the number of species present, as well as the abundance of each species. The Simpson’s index represents the probability that two randomly selected individuals in the habitat belong to the same species. The Shannon-Weiner Index is similar to the Simpson’s index in that it takes into account the species richness and the proportion of species within a zone.

Today we will use Simpson’s Index to calculate and compare species diversity from a site before and after sheep grazing. Refer to page 49 in your text books.