Biodiversity of Soil Animals

Carolina Labsheets™

In this lab, students use a Berlese funnel to take samples of soil-dwelling animals, and then compare the numbers and kinds of organisms collected from different habitats.

Needed Materials

Berlese funnel(s) (654148)

ring stands (707169)

lamps 40-watt incandescent bulbs

support stand for each lamp

70% isopropyl alcohol (972924) (or other alcohol)

cheesecloth (712690)

trowel(s)

plastic bags, 15 cm × 15 cm × 5 cm or larger (for holding samples) (713093)

metric rulers (702613)

petri dishes (741250)

index cards

newspaper or paper towels

dissecting microscopes (591815)

Optional Materials

Isopropyl alcohol evaporates rapidly, and if the collection vial dries out, specimens can be lost. This can be prevented by adding a few drops of glycerol (865530) per 100 mL of isopropyl alcohol. Hand lenses can be substituted for dissecting microscopes. Most of the specimens collected will be white. A circle of black paper placed on the stage of the dissecting scope will make the specimens show up better for counting. Probes for moving the specimens can be constructed from toothpicks and hairs. Attach a hair to a toothpick with nail polish or fast-drying glue. Cut the hair so that it extends about 5 mm past the tip of the toothpick.

Safety

Ensure that students understand and adhere to safe laboratory practices when performing any activity in the classroom or lab. Demonstrate the protocol for correctly using the instruments and materials necessary to complete the activities, and emphasize the importance of proper usage. Use personal protective equipment such as safety glasses or goggles, gloves, and aprons when appropriate. Model proper laboratory safety practices for your students and require them to adhere to all laboratory safety rules.

This activity requires the use of electricity and an incandescent bulb that can become very hot. A 40-watt bulb is recommended. In no case should the wattage exceed 60.

Procedures

Students can work singly or in groups of 4. If performed by a single student or a single group, it is best to provide two funnel setups, so that two habitats can be sampled concurrently. If this is not possible, refrigerate the first sample while the second is being extracted.

Set up a workstation for each Berlese funnel. In addition to a Berlese funnel and ringstand, each station should be supplied with sheets of newspaper or paper towels, alcohol, cheesecloth, a lamp equipped with a 40-watt incandescent bulb, and a support stand or other method of suspending the lamp above the funnel.

For sample collection, each group will need a trowel, a metric ruler, an index card (and a writing instrument), and a large plastic bag capable of holding a sample sized 15 cm × 15 cm × 5 cm.

Optional: Nematodes are common in most soils but are greatly underrepresented in extractions done with a Berlese funnel. A simple method of extracting nematodes is to set a circle of mesh (e.g., a metal window screen) into a bowl, wrap a soil sample in cheesecloth, and set this on the mesh. Add springwater or dechlorinated tap water to the bowl until the mesh is barely covered. Let the bowl sit for 1–3 days. Nematodes and other organisms will drop from the soil into the water, where they can be collected and examined.

A dichotomous key (“Identification Key for Soil Animals”) is provided with the Student LabSheet. However, an Internet search will yield a variety of more-detailed identification keys, if one is desired.

Answer Key to Questions Asked on the Student LabSheet

Answers will vary depending on the data collected. The following sample data and answers are based on samples taken from a hardwood forest and a pine forest.

Data Table of Soil Animals Collected from Habitat 1: Hardwood Forest

Data Table of Soil Animals Collected from Habitat 2: Pine Forest

1. Determine the density of animals per square meter by dividing the total number of animals collected by the surface area of the sample (15 cm × 15 cm = 225 cm2 ) and multiplying by 10,000 cm² .
   1. Population Density per Square Meter of Hardwood Forest (Habitat 1)
      = 53/225 cm² × 10,000 cm²
      = 2,356
   2. Population Density per Square Meter of Pine Forest (Habitat 2)
      = 25/225 cm² × 10,000 cm²
      = 1,111
2. Which of the habitats you sampled has the higher density of soil animals?
   Habitat 1, the hardwood forest, has the higher density of soil animals.
3. Calculate the relative abundance of each type of organism by using the following formula. Record your results in the Data Table of Soil Animals for the appropriate habitat location.
              Relative Abundance = n_i /N
   
   where
   N = total counted for all organisms
   n_i = total counted for the organism
   
   Example: Consider the following count for birds in a backyard.
   
   

   Bird	Count (Absolute Abundance)
   Cardinal	4
   Robin	8
   Song Sparrow	5
   Towhee	2
   Total Counted	19

   
   Relative Abundance for Robins = 8/19 = 0.24
4. Which organism in your sample had the highest relative abundance?
   1. Habitat 1: Mites had the highest relative abundance.
   2. Habitat 2: Mites had the highest relative abundance.
5. Which organism in your sample had the highest absolute abundance?
   1. Habitat 1: Mites had the highest absolute abundance.
   2. Habitat 2: Mites had the highest absolute abundance.
6. Is there a difference in the information given by relative abundance and absolute abundance? If so, explain the difference.
   Absolute abundance only describes how many individuals of a type were found in the sample. Relative abundance provides information about the abundance of the organism compared to the total number of organisms in the sample.
7. The diversity of a habitat refers to the number of different species found there. The Simpson Index of Diversity is one measure of diversity. Values of the Simpson Index range from 1 (infinite diversity) to 0 (no diversity). The Simpson Index for the above data on backyard birds is calculated as follows:
             D_s = 1 – [∑n_i (n_i –1)/N(N–1)]
   D_s = 1 – [4(4–1) + 8(8–1) + 5(5–1) + 2(2–1)/19(19–1)]
        = 1 – 90/342
        = 1 – 0.26
        = 0.74
   
   Calculate the Simpson Index of Diversity for your data, and record it here:
   1. Habitat 1: 0.94
   2. Habitat 2: 0.30
8. Does the Simpson Index indicate that your habitat has high or low diversity?
   1. Habitat 1: The index indicates high diversity.
   2. Habitat 2: The index indicates low diversity.

1. Is the body of the vinegar eel segmented or unsegmented?
   Unsegmented
2. Does a vinegar eel have an anterior end? How can you tell?
   Yes. They swim in one direction, with the anterior end forward unless they encounter an object, in which case they briefly reverse and then go forward again.
3. Where is the mouth located?
   At the extreme anterior end.
4. Trace the digestive tract. This is best done with one of the large female worms and will probably require adjusting the iris diaphragm to achieve greater contrast. Vinegar eels are sometimes said to have a tube-within-a-tube body plan. Is this a good description, if so, why?
   Yes. The body wall forms the outer tube, and the digestive tract forms the inner tube.
5. Do you see eyes or other specialized sense organs?
   No
6. Muscles produce movement by contracting. Many invertebrates that lack exoskeletons have either one or two groups of muscles responsible for movement. Longitudinal muscles shorten or flex the body when they contract. Circular muscles constrict the body. Circular muscles often produce waves of contraction that move along the body. Which type or types of muscles do vinegar eels have? How do you know?
   They have longitudinal muscles only. Their bodies bend but do not constrict.
7. The following major animal phyla all include some worm-like forms. (Characteristics given may apply only to the worm-like members of the phylum rather than to the entire phylum.) On the basis of your observations, to which of these phyla do you think vinegar eels belong?
   Nematoda