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A diversity index is basically a mathematical measure that contains information on how many different types or categories (like species) there are in a data set and how evenly the individuals or basic units of these species are spread amongst those types.There are many indices for measuring biodiversity and new ones are being created all the time. Different indices are used for different purposes and each index has its benefits and drawbacks. This page describes some of the commonly used indices and has links in the description of each index that leads to a page that deals with how data should be analysed to derive that particular index for your data set. Also since the mathematical treatment undergone by the data for each index is different, the different indices cannot be compared to each other, only the values of the same index for different areas can be compared.

The bottom of the page contains more information that will help you decide when you should use a particular index.As this website expands more indices and their means of data analysis will be put up.

 

Species Richness -

The species richness is the least sophisticated index. It is the sum total of all the different species in the data set.

Uses –

It is often used as a measure for estimating the conservation value of an area. As the more species an area has the greater the conservation value of that area.

Advantages –

The species richness index is very simple and does not require any mathematical treatment of the data set apart from counting the number of species in the data set.

Disadvantages –

1)The index does not provide information relating to the abundance of the various species or the abundance of different species in relation to each other (which is called the relative abundance distribution).

2) The index does not provide information relating to the identity of the species. Thus two areas may have the same species richness index but one area may have a larger number of endemic species (species found only in that area and no where else in the world) and the other area may have species commonly found elsewhere. Thus in this case the former site would be of higher conservation value.

 

Shannon-Wiener Index -

The Shannon-Wiener index has historically been quite a popular diversity index, though it's use in recent times has reduced in favour of other newer indices. The index takes into account two quantifiable measures, the species richness and the species equitability. The species richness is explained above. The species equitability deals with how evenly the individuals found in an area are dispersed amongst the total number of species, (for example if there were 20 birds found in an area with 2 individuals being found belonging to each species, with the number of species totalling to 10, we could say that the there is high equitability in the data set, conversely if there were 20 birds being found with 17 belonging to one species and the remaining three belonging to 3 different species the equitability would be very low). The Shannon-Wiener index is also called the Shannon-Weaver index and the Shannon entropy.

Use – The index is used to quantify entropy (surprise or predictability). The more different species there are in a data set and the more equal their proportions with respect to each other the more difficult it is to correctly predict which species the next randomly selected individual will belong to. A value of 0 indicates that there is only one species and there is absolute certainty that the next individual randomly obtained belongs to that species. The index approaches 0 the more individuals there are in one particular species as compared to others. Conversely a high value will indicate a low probability that two randomly selected individuals belong to the same species. Thus the index is a good indicator of whether an area has one or a few dominant species with very high abundance as compared to the rest of the species.

Advantages -

The index takes into account species equitability and richness.

Disadvantages -

The index is relatively sensitive to changes in rare species.

 

Next -

Analyzing data to obtain  the indices given above

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References

Magurran A. Measuring Biological Diversity