Bunker Hill Community College Environmental Science Discussion

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BEFORE YOU BEGIN: Review, in depth, the document in “General Course Information” titled “How to Write Your Lab Report”. In addition, review the examples provided, and make use of the template that is found in that area. In order to be considered complete, all lab reports must include the required five sections (intro, objectives, hypothesis, results, and discussion). And lastly, consider the depth and substance of the discussion sections in the examples provided. You are expected to include the same level of depth in your own discussion section.


“Biodiversity” – rarely does a discussion about ecosystem health and conservation pass without this term being mentioned. What is the big deal about biodiversity? The big deal is that many scientists believe preserving biodiversity is the best way to insure the health of individual organisms, ecosystem and the planet as a whole. You have already seen how interdependent species within and ecosystem are. Food-webs, and energy flow are two very obvious examples of such interdependence. The removal of one species from an ecosystem can have a detrimental effect on many of the other organisms residing within the ecosystem.

With destruction of the natural habitats we are currently facing, a loss of biodiversity greater than during the fall of the dinosaurs. However, if scientists are to analyze how ecosystems function and demonstrate the importance of maintaining biodiversity they must have a way to measure biodiversity. A number of different mathematical indices have been developed that allow scientists to quantify (produce a standardized number) the diversity of an ecosystem. In this lab you will be using one index called the Simpsons index to compare shrub/tree diversity and invertebrate diversity between two locations.

Measuring Biodiversity Using Simpson’s Index

An index is a mathematical formula used to quantify and assess any number of properties in a natural system. The Simpson’s Index has been developed to assess biodiversity. It is based on the probability of finding a specific species if you were to select random samples from an area. It places greater weight on more common species than on rare ones. The Simpson’s Index is used by many scientists to quantify biodiversity.

Please see the two documents below this one that walk you through how to calculate the Simpson’s Index.


A measuring tape or meter stick.


Select a site where you can measure the biodiversity of trees/shrubs and invertebrates. Ideally you will have a forested area, however, you could go to a field or park if that is all that is available to you. If you select an area with very few trees that portion of the lab may not work well, however, invertebrates are everywhere so that portion will still work. Since, you are going to compare two areas you may want to select two very distinct areas for example, a forest and a field.

Once you have selected your first area – measure out a 10 X 10 meter square plot. Mark the corners of the plot with stick or stones so that you can see the square area. Record a general description of the area include what the ground looks like, the amount of sun, if it appears to be dry or wet and any distinguishing characteristics that you think might influence the biodiversity of the plot.

Once you have recorded the species and individual data for your plot move to a new location. Pick a second plot one that you think will be different. Collect tree and invertebrate data in your new 10 X 10 M plot. Repeat the procedures used above.

Tree and Shrub Biodiversity (NOTE: Can be accomplished in all seasons)

Next, examine the trees and shrubs (plants with a woody stem, ignore flowers, weeds, grasses etc.) found within your plot. Look at the leaves and bark of the trees and shrubs – write down how many different species you have. Next record how many individuals of each species you have in the plot. You do not need to identify the trees and shrubs you just need to know if they are different species. Looking at leaves and bark should allow you to distinguish between different species.

Invertebrate Biodiversity (NOTE: If you are taking this course when there is snow on the ground, this section cannot be done. Instead, complete two different Tree/Shrub plots)

After recording the tree/shrub data do the same for invertebrates. Invertebrates are organisms without a backbone or spinal cord. Insects, spiders, centipedes, worms, snails, millipedes, flies etc. are all examples of invertebrates. Be careful and systematic when you search for invertebrates. Think of your plot as being divided into 10 one meter bands (figure 1). Carefully walk down each band looking on the ground, under rocks and leaves for invertebrates. As with the trees/shrubs write down the number of different species and the number of individuals of each species within the plot

Writing your Results Section

Calculate the Simpson’s Index number for your tree/shrub data and your invertebrate data (separate calculations). You should be calculating four index numbers – Plot 1 trees/shrubs, Plot 1 invertebrates, Plot 2 trees/shrubs, and Plot 2 Invertebrates. Put your data in a table like the one shown in the example.

Writing your Discussion Section

With depth and detail, compare the index numbers between plots and discuss possible environmental factors that influence the difference in the biodiversity between the two plots.

With depth and detail, discuss the purpose and usefulness of an index number for biodiversity. Why not just count the species?


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