Species Richness Is the Total Number of Species Present in the Community

Name: ______Date: ______Period: ______

Measuring Biodiversity

Biodiversity is the population heterogeneity of a community, or the number of species in a given area. Species diversity is a combination of species richness and species evenness.

Species richness is the total number of species present in the community.

Species evenness is the relative distribution of individuals among the species in a community. Evenness is not the same as dominance, and is maximized when all species have the same number of individuals.

Maintaining biodiversity is important for a variety of reasons:

• Diverse communities are generally less susceptible to perturbation (disturbance) than similar but less diverse communities.
• Biodiversity provides an aesthetic value that humans find appealing.
• Genetic diversity in crop plants and their wild relatives provides breeders with the "raw material" needed to select for traits in response to new agricultural challenges.
• New medicines have been discovered by screening diverse ecosystems.

Factors that control plant diversity can be natural or human-influenced.

• Plant diversity can be affected by abiotic factors like amount of available sunlight or water, variations in pH or soil temperatures, and the quality of soil nutrients or proximity of bedrock.
• When pollution is present, biodiversity is typically lower.
• When a human disturbance has occurred in a community, biodiversity is usually lower.

Simpson's Diversity Index is a way to quantify, or measure, the biodiversity of an area by comparing species richness and species evenness.

When maximum diversity occurs, the value of the index is zero and when minimum diversity occurs, the value of the index is 1. The range is therefore 0 - 1 with an inverse relationship between diversity and the index value.

Below is an example of the distribution of species in four hypothetical areas. The table below shows the species number and distribution for a few different scenarios that might exist, and the value of Simpson's index in each case.

Check For Understanding:

1. In the table above, which site exhibits the most diversity?

2. Which site has the least amount of diversity?

3. Explain why Site B has a better diversity rating than Site C:

Interpreting Results

Data Table: Variety of Tree Species at two locations in Virgina in 2003

Analysis:

1. How many species of tree grew at each of the locations? Chesterfield Co. ______Narrows ______

1. If diversity were just a measure of numbers of species, which location would be the most diverse?

1. How many individual trees grew at each location? Chesterfield Co. ______Narrows ______

1. If the diversity were just a measure of number of trees, which location would be the most diverse?

1. Which forest community had the most even distribution of trees?

1. What is the best indicator of diversity, the number of species, the number of individuals, the evenness, or a combination of all three indicators? Why?

1. At this point, which forest community do you think is the most diverse? Explain how you reached this conclusion.

1. Calculate the Simpson's Diversity Index for Chesterfield County. Show your work in the space below.

D = ______

1. Calculate the Simpson's Diversity Index for Narrows. Show your work in the space below.

D = ______

1. Using the Simpson's Diversity Index, which community is the most diverse? Explain your answer.