Biodiversity and the Shannon-Weiner Diversity Index

  The number of species in a biological community is termed Species Richness (N).  For example the tropical rain forest has more species richness than the hardwood forests of Harriman.  Species diversity, on the other hand takes into account the relative abundance of a species and not just its occurrence.  If a community is composed of s few species, or if few species are abundant, the Species Diversity will be low.  For example, in a community of 100 individuals distributed among 10 species, the maximum possible diversity would occur if there were 10 individuals of the 10 species.  High species diversity indicates the presence of a complex ecological community.  The community would exhibit a complex food web along with a great variety of ecological niches.  The minimum diversity would occur if there were 91 individuals and 1 each of the other nine. 

          Historically, one of the most commonly used measures of species diversity is the Shannon-Weiner Diversity Index.

The equation is :

H= -sum(p_ilnp_i)

   The term p_i is the decimal ratio of individuals of a species to the total number of individuals overall.  The S-W Index is used to measure habitat quality which may be degraded by human activities.   High diversity means that there is a high degree of uncertainty in predicting the next organism you will see in the ecosystem.  A low S-W Index means a high degree of certainty in predicting the next organism, meaning there are few chances of crossing paths with anything else.   The S-W Index ranges from 0.0 to approximately 4.6   A value of 0.0 means that every organism in the sample is the same species and 4.6 means the number of individuals are evenly distributed among numerous species.  The values in the middle are not terrifically descriptive and must be interpreted with care.

Part A:

In this lab you will calculate the S-W Index for the following data.

  Show your calculations and describe the diversity of this community.

Part B:  Compare the diversity of the rice field to the Costa Rican wetland, Quebrada Mula.