Calculating Flying Insect Biodiversity Using Simpson's Diversity Index

Content standards

Next Generation Science Standards:

• HS-LS2-2. Use mathematical representations to support and revise explanations based on evidence about factors affecting biodiversity and populations in ecosystems of different scales.

AP Biology

BIG IDEA 4: SYSTEMS INTERACTIONS- Biological systems interact, and these systems and their interactions exhibit complex properties. All biological systems comprise parts that interact with one another. These interactions result in characteristics and emergent properties not found in the individual parts alone. All biological systems from the molecular level to the ecosystem level exhibit properties of biocomplexity and diversity. These two properties provide robustness to biological systems, enabling greater resiliency and flexibility to tolerate and respond to changes in the environment.

Unit 8: Ecology
     8.3: Population Ecology
     8.6: Biodiversity

AP Environmental Science

Big Idea 2: Interactions Between Earth Systems-

The Earth is one interconnected system. Natural systems change over time and space. Biogeochemical systems vary in ability to recover from disturbances.

Unit 2: The Living World: Biodiversity
     2.1: Introduction to Biodiversity

Biodiversity is a hot topic. In the wild, habitats are shrinking and species are becoming extinct—lost forever—some without humans even discovering them. Biodiversity is also an issue closer to home. Planting large fields of a single genotype crop (e.g., corn or wheat) can make food sources vulnerable if that genotype becomes susceptible to a new pest or drought. An entire crop can be lost. In contrast, wild populations are more genetically diverse, so some individuals usually survive adverse conditions.

When studying the biodiversity of a community, a simple survey of the number of different species (species richness) in an area seemingly would give a clear picture of the diversity. As the following example illustrates, a calculation of the species richness alone doesn’t give that clear picture. It’s not until the distribution of those species (also called species evenness) is added to the calculation that the biodiversity of a community is more accurately portrayed.

Species richness and species diversity

Looking at the 2 communities below, compare the species richness and the species diversity using the Simpson’s Diversity Index. Note: For this activity, we will assume that each different morphotype of insect collected represents a species.

Species richness (R) is based solely on the number of species (or morphotypes) found in a given area and does not reflect the relative dominance of any species. The formula for species richness is:
R = s
Where s = the number of morphotypes

So for the example of the communities above, species richness is
R_A = 3
R_B = 3

Simpson’s Diversity Index

Simpson’s Index is one of the simplest calculations that takes into account species evenness within a community. Simpson’s Index (D) is dependent on the number of species and their relative dominance. It indicates the probability that both organisms in a randomly drawn pair are from different species. The formula is:

Where
s = the number of species (morphotypes)
i = a given morphotype
n_i = the number of individuals of morphotype i
N = the total number of individuals collected (for all morphotypes)

D will equal 0 for a community with a single taxon (with no possibility of individuals being from different species) and will approach 1 as diversity is maximized.

Objectives

Activity

This activity is appropriate for a class of 32 students working in groups of 8.

Time requirement

Sticky trap preparation and installation      30 min
Insect trapping                                        At least 1 hr (can leave traps in place overnight)
Insect collection                                      30 min
Analysis of data                                      30 min

Materials

Safety

Use caution when collecting living samples since they can include harmful organisms.

Preparation (teacher)

Note: This activity is best done when there isn’t a lot of air moving. Wind can dislodge sticky traps.

Procedure (students)

1. Punch a hole in the top of each sticky trap.
2. Using a permanent marker, label each trap with your group letter and number traps from 1 to 25.
3. Go outside.
4. As a group, decide which designated flying insect habitat to study. Consider how you will use the paper clips and string to ensure that all 25 sticky traps are in a single habitat. Secure the traps to branches, fences, or between 2 immovable objects (using tightly tied string). Best results occur 3 to 5 ft off the ground. Note: Be sure the traps are in a single habitat and are set at the same general height and in the same general conditions. Setting traps in multiple conditions will skew the results.
5. After setting each trap, remove the wax paper from the sticky trap.
6. Return to the classroom.
   Note: Wait at least 1 hour or, if necessary, until the next class period.
7. Go outside, collect the sticky traps, and return to class.
8. Place your group’s sticky traps in numerical order and use a hand lens to examine the specimens.
9. As a class, decide on consistent morphotype name designations (e.g., black spotted, red dotted, small black, big brown, or large round) for samples. Then enter the chosen names for morphotypes into the table (see Figure 1 for an example). This allows for combining data accurately later in the activity.
   
   

Figure 1 Example Data Table of Morphotypes (using class-designated names)

# of Morphotypes (s)	Morphotypes (i)		ni	(ni/N)	(ni/N)2
1	Red spotted
2	Black speckled
3	Green lacy winged
4	Tiny black
s=4	Totals ( ):	N=		Simpson=1 –
				Simpson=



10. Divide the 4 groups of students into pairs. Then divide the sticky traps evenly among the pairs of students. One of the student pair identifies the insects and, using the agreed-upon names for morphotypes, the other student counts and records the number of each morphotype in the Sample Data Table (see Figure 2).
11. After all of the data from each student pair is entered into the data table, calculate the species richness and Simpson’s Diversity Index for each habitat.



Figure 2 Sample Data Table

# of Morphotypes (s)	Morphotypes (i)		ni	(ni/N)	(ni/N)2
1	Red spotted		3	0.333	0.111
2	Black speckled		4	0.444	0.198
3	Green lacy winged		1	0.111	0.012
4	Tiny black		1	0.111	0.012
s=4	Totals ( ):	N=	9	Simpson=1 –	0.333
				Simpson=	0.667

Questions