Species Diversity

Introduction:

Most ecosystems possess a wide variety of species, as well as abiotic characteristics (i.e., water, soil, temperature, pH, etc.). All these components interact to form working natural communities, just like how towns & cities have areas of nature, neighborhoods, stores, public transportation and local governments all work together to have functional, healthy human-run communities. A standard way to assess the health & diversity of an ecosystem is to evaluate its species richness & species evenness, two aspects of the overall term of ecosystem diversity or biodiversity. Species richness is defined as the number of different types of species found. Species evenness is the proportion of each species present. As an example, if 100 individuals in an ecosystem are counted and there are 30 different species, one could say the ecosystem has a high degree of species richness. However, if out of the 100 individuals there are 75 belonging to one species (i.e., “species A”), 20 belonging to a “species B”, and the remaining 5 individuals each belonging to other species, one can say the species evenness is low.

When ecosystems undergo change, especially those caused by human activities, both species richness & evenness are changed. Even a small degree of change can drastically affect the overall functionality of an ecosystem, just like how closing a store or vital business in a town drastically affects the community & its citizens. As such, a major concern in the fields of ecology & conservation biology is to preserve biodiversity of ecosystems. Healthy ecosystems with high biodiversity provide humans with a myriad of benefits such as water purification, flood & erosion control & physical resources such as medicines. With human alteration of environments (i.e., development of infrastructure), both natural communities and humans can be negatively impacted, even if the latter doesn’t immediately realize it. For example, it is estimated that Earth has lost one-third of its forests (an area equaling double the land of the United States) in the past 10,000 years. Furthermore, half of the said change has occurred in the last century alone. With the loss of forest habitat, humans lose out on many economic benefits such as timber, potential cures for diseases, & aesthetic beauty that is connected to recreation & mental health.

In this lab, species richness & diversity of plankton will be calculated at two different field sites. On site will be artificially disturbed by human activities, and one site will be relatively undisturbed. Since plankton serve as the beginning of many food chains, they are easy to sample and study for species richness & diversity. Furthermore, diversity can be quantitatively calculated by using an equation known as the Shannon-Wiener Index (presented below). Both qualities of species richness & evenness can be evaluated by this single equation.

H = Ʃ pi (ln pi)

The Shannon-Wiener Index is represented as “H”, pi is the proportion of species “I” in your sample, & ln stands for natural log (logarithm).

In utilizing the species evenness example in the first paragraph above, the proportion of species A is 75% (or 0.75 for the equation), the proportion of species B is 0.20, and the remaining five individuals belonging to five different species will be 0.01 each. For each species, multiply pi by its natural log value, then add the values all up to get H. Therefore,

H = (0.75)(-0.29) + (0.20)(-1.61) + (0.01)(-4.61) + (0.01)(-4.61) + (0.01)(-4.61) + (0.01)(-4.61) + (0.01)(-4.61)

H = 0.77 (the negative sign is dropped only after calculating the sum)

The higher the value of H, the higher the diversity. A value of 0 indicates only one species in an ecosystem. The one limitation of the equation is that the sum doesn’t indicate whether the diversity is owed to a high species richness, evenness, or from both.

Materials:

• Dippers for water sample collection
• Two bottles or jars for storing water samples
• Two eye droppers or pipettes
• Microscope
• Microscope slides
• Disposable gloves
• Calculator

Hypothesis:

Compose a hypothesis on where you would expect to find a higher species evenness and richness, at the undisturbed or the disturbed site. Record it in the space below.

Procedure (In the Field):

1. The instructor will take the class to two different aquatic field sites, one undisturbed & one disturbed. Organize into lab groups. Each group will need a dipper and two bottles. Each person involved in sampling will need to wear disposable gloves.
2. At the first site, observe the general area and write the prompted observations in the field notes section below.
3. The instructor will guide on the proper use & collection of the water sample using a dipper. Fill one bottle and label it as disturbed or undisturbed. It might be useful to have one lab group member pour the dipper & to have another group member hold the bottle steady.
4. Travel to the other field site and repeat steps 1-3 above.

Procedure (In the Lab):

1. Once at a microscope, use a pipette or dropper and extract one sample. Place a few drops of one sample onto a microscope slide. No cover slips are needed.
2. Place the sample under the microscope & adjust the magnification and microscope stage for clear viewing.
3. Record the number of different microorganisms & the quantities observed in either data table 1 or 2, depending on which sample type is studied first. Exact identification of organism species names is not necessary! Only general descriptions are needed. For example, green & round is species 1 & brown & square is species 2.
4. Once the entire sample slide is studied & the number & type of organisms are recorded, rinse off the slide & set it in a designated place to dry.
5. Repeat steps 1-4 above with the other sample type.
6. Calculate the Shannon-Wiener Index for each sample area in data tables 1 & 2.

Field Notes

1. Observations on vegetation, ground cover, clarity of the water.
   • Disturbed site –
   • Undisturbed site –

2. Observations on slope & location.
   1. Disturbed site –

1. Undisturbed site –

3. Miscellaneous observations that are noteworthy.
   1. Disturbed site –

1. Undisturbed site –

Data Table #1 – Undisturbed Site

Name of area:

Data Table #2 – Disturbed Site

Name of area:

Post-Lab Questions:

1. Was a difference in plankton abundance observed between the two study areas? Why could this be? Be sure to utilize calculated H values in the answer.

2. Was a difference in plankton diversity observed between the two study areas? Why could this be? Be sure to utilize calculated H values in the answer.

3. How might any differences in observed plankton diversity affect both aquatic communities studied. This can be thought of as a link between the summary of the findings and potential implications of both communities.

4. Describe any potential sources of error during this lab, even if your hypothesis was proven correct!