APES
Name __________________________
Diversity Index Lab
Introduction
Biological diversity refers to the variety of organisms in a habitat or an ecosystem. It can be studied at several levels. For example,
an area interspersed with croplands, grasslands, and woodlands will have greater ecosystem diversity than an area where the
woodlands have been converted to grasslands or croplands. A native grassland with 100 species of grasses, forbs, shrubs, will have
greater species diversity than the same are after heavy grazing has eliminated many of the perennial grass species. A less obvious
level of diversity is genetic diversity within a species. If you were to examine two members of the same species from different parts
of their ranges, you might find that they differ in certain ways. As an example, consider four of your classmates. Are they identical?
What you see is genetic diversity with the species Homo sapiens. Much of this variation can be attributed to differences in the genes
those individuals inherited from their parents.
Generally, the concept of biological diversity is easiest to understand at the species level. Species diversity may simply be a measure
of the number of species in that given area, but arriving at an accurate estimate of the number of species in a natural habitat is not
always simple. It should be remembered that when habitats are disturbed, the first factor that is affected is diversity. Thus, an
index of diversity can be used to compare healthy and disturbed habitats or to determine that damage that has occurred in a
habitat.
The diversity index is a formula that has been developed to compare healthy and disturbed habitats. What does a diversity index
number mean? The highest or greatest diversity index possible is a 1.0. An example might be a tropical rainforest or a coral reef.
The lowest diversity index is a 0.01, and it might represent an area that has been severely damaged or a cultivated field of crops.
Any values above 0.5 usually indicate a relatively diverse population. For example, a healthy forest or woodland should have a
diversity index of 0.7. An area that is not very diverse, like a cornfield, might have a diversity index of 0.02 or less.
Prelab
1. In a particular forest, five species of trees can be found. A forester chooses an area and walks along a straight line (a
transect) and identifies each tree. The results are recorded on the forester’s data sheet as shown below. Thirty-three
trees were identified along this transect.
CAEDEEEDDDDDAAAAABBBBBEEECCCDDDDD
To figure the number of consecutive occurrences of a species (runs), draw a line above or below each identical
set of letters.
The diversity index is calculated by dividing the number of runs by the total number of organisms.
2. Calculate the diversity index for the class by
(a) card
(b) suit
(c) color
Procedure
In this investigation, each bag of candy represents a different habitat. Each color represents a different plant in the
habitat; select a letter to represent each color.
Randomly remove 30 candies from your bag, one at a time. Save them, but do not return them to the bag until you are
finished. Record the colors below:
Calculate the diversity index:
Put the candies back in the bag and repeat. Record colors:
Calculate the diversity index:
Questions
1. Can you suggest what kind of habitat might be represented by the diversity index of your bag—a rainforest? A
deciduous forest? A cornfield?
2. Why are populations that are more diverse usually more stable?
3. Assume two habitats have the same number of species. One habitat is predominantly one species with just a few of
the other species. The other habitat has equal numbers of all the different species. Which will have the highest
diversity index?
4. There are many human-caused losses of biodiversity, such as habitat destruction and introduction of invasive
species. Are there any natural events that could alter the diversity index? Give a few examples.
5. How do invasive species change the diversity index?
6. What do you think would happen to a habitat if the plant diversity declines?