This is a legacy topic. View the most up to date content by clicking an exam board tab above or visiting the home page.Community #1 has 150 individuals per each of 20 different species (3000 individuals in total)
Community #2 has 10 individuals per each of 19 species, and 2990 individuals of the last species (3000 individuals in total) It doesn't take a complex formula to figure out that community #1 is far more diverse compared to community #2, despite them having the same number of species and individuals.
The distribution of individuals to species is important in determining a community's diversity.The above example is easy enough, but for most purposes a
formula is needed. This formula measures the index of diversity, which is simply a measure of diversity in a community. By calculating it and obtaining a numerical value, different communities can be easily compared.Right, here it comes...
No, don't run away yet! Wait and see how easy it is to work out.
D = Diversity index
N = total number of all organisms
n = total number of organisms of each species
Σ = sum of
Now it's simply a matter of replacing numbers. Look, I made it all purple so you would enjoy looking at it. Let's work out the index of diversity for community #1 (from above).
Firstly, we need a value for N. What's the total number of organisms? 3000. Sorted.
Next, we need a value for N - 1. No calculators! ...2999, sorted.
Finally, we need a value for n and n - 1. n = 150, while n - 1 = 149.
Drawing up a table helps:
3000*2999 8,997,000
So, D = ----------------- = --------------- = 20447000 44700020 in this case is
maximum diversity (there are 20 different species). If the index was 1, then diversity would have been non-existent. An index of 10 would indicate moderate diversity.Now work out the index of diversity for community #2 using the table above and the walk through as a guide. You should get a pretty low value. I know it's a bit confusing that the above numbers are identical in all the columns, but if you work out community #2 then the values for 1 species should be different to the other 19.
Most of the time all species will have different values. The working of it is the same though. |