Download Lab #9: Ecology (Day 1)

Bio 213
Name:_______________________
Lab 9: Leaf litter Invertebrate Biodiversity
INTRODUCTION
In this field study we will quantify the diversity of the invertebrate communities from 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 composed of almost totally one species
and would not look diverse.
diversity.
Table 1. A comparison of two communities and their apparent
Number of Individuals
Community 1
Community 2
20
92
20
2
20
2
20
2
20
2
100
100
Species
A
B
C
D
E
TOTAL
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)
∑ ni (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, leaf litter is a dynamically active
living community. The organisms are busy using leaf litter as a place to feed, reproduce,
compete…live! In the process, they work the leaf litter into 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 leaf litter 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 food 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 leaf litter animals and study this complex and highly
intriguing community. This exercise will take several days to complete.
OBJECTIVES
In this study, you will
a) identify various groups of animals that live in leaf litter.
b) explore concepts of ecosystem ecology.
DAY ONE: SAMPLE COLLECTION
MATERIALS
Burlese funnel system
specimen vials, with alcohol
bucket for leaf litter
trowel
PREPARATIONS
1. In class, we will determine where we want to sample for leaf litter invertebrates. We will choose
several sites for analysis, and several groups will collect samples from the same locations.
FIELD PROCEDURE
1. Work in groups of 3-4.
2. Get a trowel and bucket and go to collection site.
3. Write a description of the site on Tables 1 & 2. Be sure to include what kind of plants the leaf litter
is coming from, light conditions and moisture conditions.
4. Using the trowel, dig into the leaf litter. You want to take samples from the bottom-most layer
where the most decomposition is occurring, without getting soil.
5. Return to the lab and label your Burlese funnel with your site numbers and group name.
6. Place your Site 1 sample in the Burlese funnel apparatus marked Site 1. Repeat for Site 2.
7. Adjust the lamp so it is about 3 inches above your funnels and turn on the light. (Depending on
the set up, this may be already done.)
8. Label a vial “Site 1” and another “Site 2”, fill about 3/4 with alcohol, and put each under the
appropriate funnel.
9. Let the apparatus sit for several days.
DAY TWO: DATA COLLECTION
MATERIALS
dissecting microscope
squirt bottle of alcohol
specimen vials, with alcohol
Guide to common leaf litter and soil animals
dissecting probes/needles
top or bottom of petri dish
Each group will be responsible for analyzing the contents of the two sites they collected. 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.
1. Turn off the light of the Burlese apparatus.
2. Obtain your sample vials (one from each site).
3. Empty the funnels in the trash, but be sure to save the pieces of wire mesh!!
4. 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.
5. 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.
6. Place the petri plate under the microscope and sort the organisms by moving similar looking
organisms together in groups with the dissecting needle/probe. Start at low power and search for
organisms. Finish at high power, to be sure you have not missed anything.
7. Use the guide to identify the groups.
8. Count the number of individuals in each group, using "tick marks" in Tables 1 & 2 to keep track.
a. A helpful way to do this is have one group member scan the petri dish 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.
9. 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.
10. Repeat for Site 2.
DATA & ANALYSIS
Diversity: You and your lab mates will select two of the sampled communities to compare diversity.
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. Use 2 decimal places.
2.
D=
Community 1:
D=
Community 2:
3. Which community is more diverse? How would you explain your results: Why might the one
community be more diverse than the other?
4. Compare your results to your classmates. Of the various factors we tested, which was the best
indicator of biodiversity in leaf litter communities? Why?
---------------------------------------------Sample calculation for Simpson’s Diversity Index
Species
Number (n)
n(n-1)
Woodrush
2
2
Holly (seedlings)
8
56
Bramble
1
0
Yorkshire Fog
Sedge
1
3
0
6
Total (N)
15
64
Putting the figures into the formula for Simpson's Index
Table 1: Site 1 data
Description of Site 1:
Type of Animal
Thysanura (bristletails)
Collembola (springtails)
Thysanoptera (thrips)
Protura
Pseudoscorpions
Ticks
Mites
Centipedes
Millipedes
Spiders
Insect larvae
Beetles
Nematode worms
Others
Tick Marks
(keep track of numbers here)
Total
Number
Table 2: Site 2 data
Description of Site 2:
Type of Animal
Tick Marks
(keep track of numbers here)
Total
Number
Thysanura (bristletails)
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]