BIODIVERSITY OF A FIELD

Name: ______

Background

Biodiversity has become a rather hot topic within the field of ecology over the past two decades. Educationally, we have all been taught that the tropical rain forests are some of the most diverse habitats on Earth. But how is biodiversity measured? One common measure of biodiversity is called the “species richness”, which is defined as the total number of distinct species within an area and represented by the variable S. Another common measure is called “species diversity” and is calculated using the equation below.

H = -[(ni/N) ln (ni/N)]

where ni = the number of individuals of a given species in the sample area

N = the total number of individuals in the sample area

Materials

meter stick

textbook

insect killing jar

Procedure

In the Field

1. In your assigned group of three or four, acquire a meter stick and walk quietly outdoors to the field adjacent to Lamar.

2. One group member chose a number between 1 and 100 and have one other group member make one guess of the number. Determine the difference between the chosen number and the number guessed. Starting at the street walk that number of steps to the west along the mowed edge between the field and the school property (you must stay within the field area so if you walk all the way to the edge where the poison ivy is, turn and walk back).

3. Have the group member un-involved in the numbers during the last round chose a number between 1 and 100 this time, and have the group member that chose the first number guess the number this time. Determine the difference between the chosen number and the number guessed. Starting at your point along the edge of the field, walk that number north into the field (toward 119th Street).

4. Place your meter stick on the ground perpendicular to the line of walking at the point that you have located. Imagine a complete one-meter square area in front of the meter stick.

5. First, look around your meter square area and pick a sample of each of the plants in your quadrant and place it in a textbook to be pressed. Then, make a brief sketch of the species of plants in your area in the table in question 1. Record the “species richness” of the meter square area and record it at the top of question 1.

6. Next, estimate the percentage of the area that each species composes. Realize that one meter is composed of ten decimeters and that the meter square is composed of one-hundred separate square decimeters. Thus, an accurate estimate could be aided by determining how many of the hundred separate squares a particular species is found in. Record your percentages in the data table in question 1 underneath your sketches.

In the Classroom

1. Given the sample calculation that follows determine the species diversity for your samples of plants and insects. Show your work and final answer in question 3.

Species A = 20%, Species B = 80%

H = -[(ni/N) ln (ni/N)] = -[(0.20) ln (0.20)] + [(0.80) ln (0.80)]

= -[(0.20)(-1.609437912)] + [(0.80) (0.223143551)]

= -[(-0.321887582)] + [(-0.178514841)]

= -[(-0.500402423)]

= 0.50

  • Notice that ni/N is equal to the decimal representation of the percentage for each species
  • The  means to add or sum the answers for each individual species. So the equation is written twice when the numbers are substituted because there are two species. If you have more than two species your will be a longer equation.
  • When you apply the “ln” (natural log) you need to check how you input it into your calculator to get it to work. For some calculators you input 0.20 and then hit the “ln” or “LN” function button, while for others you will hit the function button and then input the number and hit equals.

Questions

1. Plant Species Richness = ______

Species A
% = _____ / Species B
% = _____ / Species C
% = _____ / Species D
% = _____
Species E
% = _____ / Species F
% = _____ / Species G
% = _____ / Species H
% = _____
Species I
% = _____ / Species J
% = _____ / Species K
% = _____ / Species L
% = _____
Species M
% = _____ / Species N
% = _____ / Species O
% = _____ / Species P
% = _____

3. Plant Species Diversity = H = ______(show the calculation below)

5. Compare and contrast primary and secondary succession. What do you imagine happens to the species diversity from the beginning to the end of such events?

6. It comes as no surprise that human are responsible for many disturbances to an ecosystem that may or may not lead to secondary succession. With reference to both pages 783 and 806-7 identify each of the major human threats to biodiversity. For each of the three threats described, explain how the threat leads to a reduction in biodiversity.