Bio 213
Name:_________________________________
Lab 10: Biodiversity in Leaf Litter
Invertebrates
OBJECTIVES
a) identify various groups of animals that live in the soil.
b) explore concepts of ecosystem ecology.
INTRODUCTION
In this field study we will quantify the diversity of the soil invertebrate communities from which we took soil
and leaf litter samples.
we will quantify the diversity of the soil invertebrate communities from which we took soil and leaf litter
samples.
Diversity is a measure of the relative representation of species in a community. It is comprised of two
components, species richness (the number of species) and species evenness (the relative number of
individuals of each species). Thus, two communities may have the same number of species (richness) but one
community may have one species that is more numerous than the others (evenness) (Table 1); the second
community would be less diverse. This makes intuitive sense, since the second community would look to us as
though it were made up of almost totally one species and would not look diverse.
Table 1. A comparison of two communities and their apparent diversity.
Number of Individuals
Species
Community 1
Community 2
A
20
92
B
20
2
C
20
2
D
20
2
E
20
2
TOTAL
100
100
There are several ways to quantify diversity. One is simply to calculate species richness. However, as
illustrated in Table 1, this can give a false impression of the relative diversity of two different areas. Therefore,
other measures have been devised by community ecologists. The one we will use is called Simpson’s index.
Simpson’s diversity index =
D
N N  1
 n i ni  1
where N = total number of individuals of all species in a community and ni = number of individuals of the
ith species or taxon. The summation symbol (∑) means to do the calculation following the ∑ for
each of the species or taxa and then add up the results of all the calculations.
D ranges from 1, for a community made up of one species (or other taxon), to infinity, for a community made
up of one individual of many species (or other taxon).
Contrary to its outward appearance to the casual observer, soil is a dynamically active living community.
The organisms in the soil are busy using the soil as a place to feed, reproduce, compete, … live! In the process,
they work the soil, making it more fertile, improving its water-holding capability, increasing the ability of oxygen
to enter the soil, and decreasing the soil's susceptibility to erosion. They therefore play an important role in the
formation of soil.
The organisms in the soil interact with one another and with the environment, and thus make up an
ecological community. Energy is transferred through the community, and nutrients are recycled. There are
predators, prey, decomposers, competitors, symbiotic partners. Plant material that drops to the soil surface,
called plant or leaf litter, as well as the bodies of dead organisms, is collectively called detritus, and becomes
food for various organisms called detritivores. They chew it up into smaller pieces, and leave fecal wastes that
then become for other organisms. Some of these organisms are eaten by predators. The detritus gets worked
to smaller and smaller particles, and bacteria and fungi, the decomposers, and chemical action reduce the
organic humus to the minerals that are nutrients used by plants. And the cycle continues.
In this laboratory exercise, we will collect soil animals and study this complex and highly intriguing
community. This exercise will take several days to complete.
MATERIALS
Burlese funnel system
dissecting microscope
specimen vials, with alcohol
squirt bottle of alcohol
Guide to common soil animals
dissecting probes/needles
top or bottom of petri dish
PREPARATIONS
In class, we will determine where we want to sample for soil invertebrates. We will choose several sites for
analysis. Based on these selections, we’ll compose our hypothesis and prediction (to be recorded in your
lab notebook.)
FIELD PROCEDURE
1. Work in groups of 3 or 4.
2. Obtain two funnels (modified pop bottles). If they aren’t labeled already, label one “Site 1” and the other
“Site 2”.
3. Collect a sample of leaf litter and soil from one or the other site, taking notes of the conditions at your site.
4. Place the samples in the Burlese funnel apparatus. Adjust the lamp so it is about 3 inches above your
funnels.
5. Turn on the light.
6. Label a vial “Site 1” and another “Site 2”, fill about 3/4 with alcohol, and put each under the appropriate
funnel.
7. Let the apparatus "go" for one week.
LAB PROCEDURE (DATA COLLECTION)
Each team will be responsible for analyzing the contents of one vial. Note that some of these samples will be
easier to analyze than others. If you are done early, help your classmates out! We cannot finish this exercise
until we have the data from every group.
NOTE: Some of these organisms are so small that you will have a hard time seeing them with the naked eye!
1.
2.
3.
4.
5.
6.
7.
8.
9.
Turn off the light of the Burlese apparatus.
Obtain your sample vials (one from each site).
Empty the funnels in the trash, but be sure to save the pieces of wire mesh!!
Return to the room and obtain a dissecting microscope, the top or bottom of a petri plate for each
member of your group, and one or two dissecting needles/probes for each member.
Work with one vial at a time. Swirl the vial, then pour the contents into enough petri plates so that each
member of your group can be working to identify and count the organisms. If you need to, use the alcohol
squirt bottles to wash out any organisms that remain in the sample vial.
Place the petri plate under the microscope and sort the organisms. Start at low power and search for
organisms. Finish at high power, to be sure you have not missed anything.
Use the guide to identify what you can.
Use table 2 (or something similar), to keep track of the number of each type of organism.
c) Sort the organisms by moving similar looking organisms together in groups with the dissecting
needle/probe. Count the number of individuals in each group, using "tick marks" to keep track
instead of counting if there are many individuals, and counting up the tick marks later.
d) One group member scans the petri plate and call out the identity of organisms they see(e.g.,
“pseudoscorpion, mite, mite, springtail, . . .”, while another group member keeps track of them by
using tick marks. Count up the tick marks when finished.
After you have finished, add up the total number of individuals for each type of organism you found. Note
that if your sample was divided into multiple funnels, you will need to pool your data with another group
before determining the Simpson’s Index.
POSTLAB
1.
Using the information above and your class data, calculate Simpson’s diversity index for each of the two
communities you have chosen to compare. (Show your work.)
2.
Which community is more diverse? How would you explain your results: Why is the one community more
diverse than the other? Do your results support your hypothesis? Explain.
3. Compare your results to your classmates. Of the various factors we tested, which was the best indicator of
biodiversity in leaf litter communities? Why?
4. What value does the Simpson’s Index offer ecologists? Why might it be useful to work with an established
index, rather than simply reporting your raw data in the literature?
Table 2: Your group’s data
Location
(write in location of
site)
type of animal
Site 1
Thysanura (bristletails)
Location:
keep track of numbers here
total number
Collembola (springtails)
Thysanoptera (thrips)
Protura
Pseudoscorpions
Ticks
Mites
Centipedes
Millipedes
Spiders
Insect larvae
Beetles
Nematode worms
Others
REFERENCES (FOR FURTHER INFORMATION)
Crossley, D. A. Jr. 1977. Pp. 49-56. In: W.J. Mattson (ed.) The role of arthropods in forest ecosystems. Springer-Verlag, New York.
Edwards, C.A., D.E. Reichle, and D.A. Crossley, Jr. 1970. Pp. 147-172. In: D.E. Reichle (ed.) Analysis of temperate forest ecosystems. Springer-Verlag, New York.
Petersen, H. and M. Luxton. 1982. A comparative analysis of soil fauna populations and their role in decomposition processes. Oikos 39: 287-388.
Luff, M.L. 1975. Some features influencing the efficiency of pitfall traps. Oecologia 19:345-357.
Smith, R.E. [ecology text]