Portsmouth, RI Location

Biodiversity Measures 
[Species Richness] [Simpson's Index] [ShannonWiener Index] 
Measuring Biodiversity Use our database numbers to estimate various measures of biodiversity. Species Richness (S)  the total number of different organisms present. It does not take into account the proportion and distribution of each subspecies within a zone. Simpson Index (D)  a measurement that accounts for the richness and the percent of each subspecies from a biodiversity sample within a zone. The index assumes that the proportion of individuals in an area indicate their importance to diversity. ShannonWiener index (H)  Similar to the Simpson's index, this measurement takes into account subspecies richness and proportion of each subspecies within a zone. The index comes from information science. It has also been called the Shannon index and the ShannonWeaver index in the ecological literature. More About Measuring Biodiversity When measuring diversity it is good to remember that what we are trying to describe is the relationship of individuals of varying subspecies within a zone. In our research, we use the number of individuals of each subspecies observed (e.g., found in each zone). There are some underlying assumptions that all the measures of biodiversity have in common:
The most common measures of biodiversity are Species richness, Simpson's index and ShannonWiener index.
However, this does not indicate how the diversity of the population is distributed or organized among those particular subspecies. For example, if there were 4 different subspecies observed in Zone 1 and Zone 2 the richness would be equal. This does not indicate what percentage of the abundance there were of each subspecies. In Zone 1, 80% of the abundance could have been Blue Jay while at Zone 2 there could have been an even 25% of each subspecies. The index, first developed by Simpson in 1949, has been defined three different ways in published ecological research. The first step for all three is to calculate P_{i}, which is the abundance of a given subspecies in a zone divided by the total number of subspecies observed in that zone.
D is influenced by two parameters  the equitability of percent of each species present and richness. For a given species richness, D will decrease as the percent of the species becomes more equitable. The researcher must observe the species patterns carefully to interpret the values effectively. Similar to the Simpson index, the first step is to calculate P_{i} for each category subspecies. You then multiply this number by the log of the number. While you may use any base, the natural log is commonly used. The index is computed from the negative sum of these numbers. In other words, the ShannonWiener index is defined as:
H = sum(P_{i}log[P_{i}]) Using species richness (S) and the ShannonWiener index (H), you can also compute a measure of evenness:
E = H/log(S) Evenness (E) is a measure of how similar the abundances of different species are. When there are similar proportions of all subspecies then evenness is one, but when the abundances are very dissimilar (some rare and some common species) then the value increases. 
[Species Richness] [Simpson's Index] [ShannonWiener Index] 
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