Aquatic ecology and Biodiversity

Unit 4- Community ecology

4.1.13. Measurement of species diversity
Determining which community has greater species diversity is easy when either species richness or evenness is held constant while the other parameter varies, but often communities will vary in both richness and evenness. Species diversity combines into a single figure, both the numbers of species (species richness) and the distribution of the total numbers of individuals among the species (species evenness). It is expressed through various mathematical diversity indices. High species diversity is the indicative of stable, healthy environment and low diversity is the indicative of stressful and fluctuating environment. Temperature, light, salinity, DO2, CO2, pressure and nutrients are known to limit the growth, reproduction, abundance, distribution, behavior and survival of organisms are called limiting factors. Scientists have developed a variety of mathematical equations (or indices) that incorporate both species richness and evenness into a single measure of species diversity (e.g., the Shannon-Wiener Index and Simpson’s Index). Different diversity indices assign different weightings to species richness and evenness, so the so most useful index to choose depends on the circumstances.

Further Reading
Magurran, A.E. 1988. Ecological Diversity and its Measurement. Princeton University Press, Princeton, NJ. ISBN: 0691084912