Community Diversity

In this experiment, you will compare the biodiversity in a less disturbed area against a more highly disturbed area. The experimental hypothesis could be that a less disturbed area will contain a greater diversity of species than a highly disturbed area. The null hypothesis could be that there will be no difference in diversity between less disturbed and highly disturbed areas.

To begin, divide into groups of four and collect a hula hoop, ball, measuring tape, set of printed tables, 10 utility flags, and an ID guide from the front of the class. You should also collect a shovel and 10 collecting bottles for the soil sampling exercise and bring these outside, too. Once in the field, your instructor will show you the two habitats you will study.

Choose one habitat to begin and place one flag in four corners to form a rectangular sampling area. Measure the length and width of the sampling area in meters, and then multiply the two numbers to determine the area. Now, standing in the middle of the sampling area, throw a tennis ball into the air.

Mark the location where it lands with a flag. Repeat this four more times to determine all five of your random sampling points. Keeping your flag at the center, place a hula hoop around it.

The area within the hula hoop is a quadrat. Then, identify all of the different species in the quadrat and record them as species A, B, and so on in table one. Once all of the plants have been recorded, use a shovel to collect one cup of soil from each of the sites and put the samples in labeled bottles.

Be sure to label the bottle with your names and the site name and quadrat number. Repeat the plant identification and soil sampling for the remaining four quadrats in the first habitat, recording your observations in table one. Once you have completed recording in the first habitat, move on to the second field, again marking out a rectangular sampling area.

Repeat the random placement of quadrats using the tennis ball, and then record the species present in each quadrat in table two. Finally, collect one cup of soil from each of the disturbed habitats'quadrats, for a total of five cups from the disturbed and five cups from the undisturbed habitats. The next part of the study will test for edge effects, or a change along a gradient from where one ecosystem type meets another to the core habitat of the ecosystem.

The experimental hypothesis is that there will be a greater diversity of species closer to the edge of the ecosystem than in the center, or core, of the ecosystem. The null hypothesis is that there is no change in diversity along the transect from edge to core habitat. Place a flag at the perimeter of the field where it meets another habitat, like a forest or parking lot.

Extend a tape measure towards the center of the field, perpendicular to the edge of the field. This will be your transect. Place a flag at the zero meter of the transect, the edge of the other habitat, then place additional flags at 10 meters, 20 meters, 30 meters, and 40 meters into the core of the habitat for a total of five flagged locations.

Starting at the zero meter point along the transect, place the hula hoop at the flagged location. Record the species present in the quadrat in table four. Then repeat the quadrant placement and species recording at the 10 meter, 20 meter, 30 meter, and 40 meter marks.

Next, place two more transects from different starting points at the perimeter of the field extending into the core area. Mark the 10 meter points along these transects, and again use these as markers to place quadrats. Record the species found in each of these quadrats in table four.

The next step is to process the soil samples. The experimental hypothesis is that the two landscapes under different disturbance regimes will differ in their soil composition and pH. The null hypothesis is that there will be no difference in the soil composition or pH between the two sites.

To begin, remove soil from one bottle of the first site sampled and fill the pH color compartment of the soil sample kit to the soil fill line. Pour the pH test capsule into the test chamber, then fill the capsule with distilled water until it reaches the water fill line. Place the cap on the compartment and shake it.

Allow the color to develop for about a minute, and then compare the soil to the color chart to determine the pH. Repeat the pH analysis for the second sampled site, filling out table three for the recorded pH. To process the soil samples for nitrogen, phosphorus, and potassium, remove 20 milliliters of soil from the bottle of the first site sampled.

Place the soil in a clean container with 100 milliliters of distilled water. Repeat this process for the second site, labeling each container, and then allow them to sit for one hour. After one hour, use a dropper to fill each of the nitrogen, phosphorous, and potassium comparators to the fill line with solution from the first sampled site.

Add the appropriate capsule to each of the comparators for each chemical test. Cap and shake the comparators thoroughly, and then compare the solution in the test chamber to the color chart, recording the results as the appropriate number on the scale into table three. Repeat the nitrogen, phosphorous, and potassium tests for each of the sampled sites.

To calculate the Shannon-Weiner Diversity for each of the observed sites, first open a new Excel spreadsheet. Label cell A1 species name, and cell B1 total count. Starting from the second row and in column A, fill in the sheet for each species found in the first site, using the data recorded in table one.

Calculate the total number of each species found in the entire sampling effort and record this in the B column of the Excel spreadsheet. Now, label cell G1 total count of all species, and in cell H1, write a formula to sum all of the count values entered in column B.Label cell C1 proportion of each species and in cell C2, type the formula for the proportion of the total of each species at the site. Drag this formula down for each row of data represented in column B.Label cell D1 natural log proportion of species and in cell D2, type the formula for the natural log of the proportion of species at the site.

Drag this formula down for each row of data represented in column C.Label cell E1 ps star ln ps, short for proportion of species multiplied by the natural log of the proportion of species. In cell E2, type the formula multiplying the proportion of species by the natural log of the proportion of species at each site, and then drag this formula down for each row of data represented in column D.Label cell G2 sum of ps star ln ps, and in cell H2, type a formula summing all of the values in column E.Label cell G3 Shannon-Weiner Index, and in cell H3, enter the formula for the Shannon-Weiner Diversity Index. This is the calculated Shannon-Weiner Diversity Index for the first sampled site, and will be used for comparison between the two sites.

Repeat the data analysis in a new sheet using the data collected for the second site, which was recorded in table two. Areas with greater index values are considered to have greater species diversity. Do you see differences between your sites?

Repeat the Shannon-Weiner Diversity calculations using a total count of all the species at each distance along the transect, then create a table similar to figure two in a new Excel sheet. Click on the Data tab in Excel, and then on the Data Analysis button. Select Regression and click Okay.

For the Input Y Range, highlight the Shannon-Weiner Diversity values, and for the Input X range, highlight the distance values. Select an output location for the regression results and click Okay. Check the P value box in the intercept row to see if there is a significant correlation between distance from edge to core habitat and biodiversity.

A value of less than 0.05 rejects the null hypothesis of no change in diversity along the transect, while a value greater than 0.05 does not reject the null hypothesis. Next, to perform t-tests for determining soil composition differences between sites, open a new Excel spreadsheet. In cell A1, type site 1:pH, and in cell B1, type site 2:pH.

Fill in cells A2 through A6 and cells B2 through B6 with the soil pH collected in the disturbed and undisturbed sites, respectively. Click the Data tab in Excel and then select Data Analysis. Now scroll down and select t-Test:Two-Sample Assuming Equal Variances and select Okay.

Click the drop down next to Variable 1 Range and highlight cells A2 through A6 in the spreadsheet, Then click the dropdown next to Variable 2 Range and highlight cells B2 through B6 in the spreadsheet. In the box for hypothesized mean difference, type zero as our null hypothesis. This means that there is no difference between the two disturbance regimes.

Leave the Labels box unchecked and set the alpha value to 0.05. Select Output Range, and in the box, click an empty space in the spreadsheet. Click Okay.

A table of t-Test results should be outputted in the spreadsheet. The relevant data are the means for each of the sites and the alpha value. If this second value is less than our alpha value of 0.05, we can reject the null hypothesis that there is no difference in pH between the two sites, and the hypothesis that disturbed versus undisturbed sites differ in their pH value would gain support.

If this value is greater than 0.05, however, we may not reject our null hypothesis. Repeat this analysis for each of the other three soil variables, creating a new spreadsheet for each of the phosphorus, potassium, and nitrogen elements. Did your results for these nutrients and the pH allow you to reject the null hypothesis?

Were the levels of nutrients different in each condition? What might this tell you?