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Unformatted text preview: Exercise 4B Measuring Biodiversity
— Invertebrate Pitfall Traps
How diverse are the invertebrates on campus?
We will examine invertebrate communities from sites on campus. Each group will place three
pitfall traps in the ground in different areas. The following lab period, we will collect the samples
and identify distinct groups of animals and measure abundance of each group. We will not be
identifying organisms to species — instead, we will work with larger taxonomic groupings
(class, order, and family) using the keys provided or online.
Once organisms are identified, we will determine taxon (“species”) richness and evenness and
calculate an index of biodiversity (the Shannon index). We will also construct speciesaccumulation and rank-abundance curves as described in the pre-lab.
Materials (per laboratory team)
Containers for pitfall traps
Guide to invertebrate identification
1. For each of the assigned sites, locate an area where your trap is unlikely to be disturbed
over the sampling period (an area with little foot traffic). Mark the site with a survey flag.
2. With a trowel or other digging instrument, dig a hole large enough and deep enough so
that your entire trap fits into the ground and the top of the trap is flush with or a little below
the surface of the soil. If the top of the container is above the surface of the soil, you will
not catch anything! Leave the traps until the next lab period. Biology 6C 89 3. The next lab period, collect the traps and return to lab. Examine your specimens using a
dissecting microscope. Using the key provided, identify the organisms in your sample. Sort
into families of like organisms and enter data into Table 4.3. Sum the number of
individuals of each group, and include these totals in the right-hand column of the table. 4. Transfer these totals to the Shannon Calculation Table (Table 4.4). Calculate H, the
diversity index for this sample, following the example from the Introduction [pre-lab]. 5. Use your value of H to calculate species evenness (J), following the example in the
introduction. 6. Enter your data in the class spreadsheet. 7. Using class data, complete Table 4.5.
Be sure the numbers entered reflect only the new groups of organisms observed (that is,
those seen for the first time in each sample). 8. Draw a species accumulation curve in Figure 4.5. 9. Using class data, complete Table 4.6.
Be sure groups are ordered by rank (from most abundant to least abundant). Include the
number of organisms observed for each family and sum to find the total number of
organisms observed. To determine the proportional abundance for a group, divide the
number of individuals in that group by the total number of organisms observed. 10. Draw a rank-abundance curve in Figure 4.6. 90 Exercise 4B. Measuring Biodiversity — Invertebrate Pitfall Traps Table 4.3 Data Table for Ground Invertebrates
# Species Identified Number of Individuals
(Tally Marks) Total number
of Individuals 1.
of individuals in the
sample: Species Richness (S) = Biology 6C 91 Table 4.4 Shannon Calculation Table for Ground Invertebrates
Organisms Found in Soil
Samples Ni Pi In Pi – (Pi· In Pi) 1.
TOTAL H= Species Evenness (J) = 92 Exercise 4B. Measuring Biodiversity — Invertebrate Pitfall Traps Table 4.5 Species Accumulation Data for Ground Invertebrates
(Sample Number) Cumulative Species Number
(only include new species for each sample) 1
8 Cumulative Number of Species Figure 4.5 Species Accumulation Curve for Ground Invertebrates Number of Pitfall Samples Biology 6C 93 Table 4.6 Rank Abundance Data for Ground Invertebrates
Rank Species # individuals # individuals / total # observed 1
Total = 94 Exercise 4B. Measuring Biodiversity — Invertebrate Pitfall Traps Figure 4.6 Rank- Abundance Curve for Ground Invertebrates Proportional Abundance (%) 100% 0%
Rank Biology 6C 95 Conclusions
For any given sample, the highest possible value of H is equal to the natural logarithm of the
number of species in the sample. For your sample, how does H compare with its theoretical
upper limit? Explain what this means.
How does the slope of your rank-abundance curve relate to your calculated J value?
What conclusions can you draw about species richness of your sample sites? Do you think
your collection of samples includes more than half of all species present at each site, or not?
Explain, using your species accumulation curve. 96 Exercise 4B. Measuring Biodiversity — Invertebrate Pitfall Traps ...
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