Why is genetic diversity important to the survival of a species?

Why is it important to measure both species richness & genetic diversity to give full picture of biodiversity?

• Answer:

  Species richness = how many species are present. Genetic diversity = how much variety is there within the community. Most biologists use a combines measure that takes into account the evenness of the community. We use indices such as the Shannon Index. Which community would you say is more diverse? A. 20 species. Species 1-19 each have 2 individuals, and species 20 has 162 individuals; or B. 20 species, all of which have 10 individuals. Both communities have the same species richness (20) and the same number of individuals (200). Community B, however, is much more even, and likely has more genetic diversity. In community A, if something happened to even 1 individual from species 1-19, that species would likely disappear entirely, as it has too few representatives to persist when something bad happens. Diversity works a bit like an insurance policy.