Measuring diversity and the reasons for maintaining it
Ex-situ and in-situ conservation
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……..