Diversity Indices (DP IB Environmental Systems & Societies (ESS))

Diversity Indices

• Communities can be described and compared through the use of diversity indices, which are mathematical tools used to quantify the diversity of species within a community

  • These indices provide a measure of the variety of species present, as well as their relative abundances, and can be used to compare different communities or to track changes in diversity over time

• When comparing communities that are similar, low diversity could be indicative of several factors, such as pollution, eutrophication and recent colonisation of a site

  • For example, pollution can have a negative impact on the diversity of a community by reducing the number of species that can survive in the area

  • Similarly, eutrophication, which is the process of nutrient enrichment in aquatic ecosystems, can lead to a decrease in diversity as a few dominant species outcompete others

  • Finally, when a site is recently colonised, the diversity of the community is naturally low as it takes time for a diverse range of species to establish themselves

• Some commonly used diversity indices include the Shannon-Wiener index, Simpson's index, and the evenness index

  • The Shannon-Wiener index is a measure of the diversity of a community that takes into account both the number of species present and their relative abundances

  • Simpson's index, on the other hand, is a measure of the dominance of a few species within a community, and is calculated based on the probability that two individuals selected at random from the community belong to the same species

• Overall, diversity indices provide a powerful tool for describing and comparing communities

• By quantifying the diversity of species within a community, researchers can gain insight into the ecological processes that drive community structure, as well as track changes in diversity over time

• Additionally, when comparing similar communities, a low diversity index may indicate that one of the communities has undergone some kind of disturbance (usually caused by some kind of damaging and detrimental human activity)

  

 A low biodiversity index may indicate detrimental human activity in a community

Case Study Example

• A study conducted by researchers in India compared the diversity of phytoplankton in a lake impacted by industrial pollution and a control lake (a similar lake that was not impacted by pollution

  • The control lake, L1, was located in a rural area and had no known sources of pollution, while the impacted lake, L2, received effluent discharges from an industrial area

• The study was conducted over a period of six months, during which time the researchers collected samples of phytoplankton from each lake and calculated the Simpson Index values for each site

  • The table below shows the Simpson Index values for each lake:

Simpson’s Diversity Index Values

• The results of the study showed that the reference lake, L1, had a higher diversity of phytoplankton compared to the impacted lake, L2

  • The Simpson’s Index value for L1 ranged from 0.81 to 0.85, indicating a high level of diversity, while the Simpson Index value for L2 ranged from 0.61 to 0.64, indicating a low level of diversity

• The data also showed that certain taxa of phytoplankton were more abundant in the reference lake, while others were more abundant in the impacted lake

  • For example, the reference lake had a higher abundance of diatoms and green algae, which are considered to be indicators of good water quality

  • In contrast, the impacted lake had a higher abundance of blue-green algae, which are considered to be indicators of poor water quality

• This study provides a clear example of how the Simpson’s Index can be used to compare the diversity of the communities in two similar habitats

  • The low Simpson’s Index value for the impacted lake indicates a reduced diversity of phytoplankton, which is likely due to the negative impact of pollution on the community