Invertebrate Biodiversity Lab

Variables

Independent Variable

Two DIFFERENT areas are being investigated as described in the introduction.

Dependent Variable

This is the number of different species of invertebrates and their frequencies.

Controlled Variables

The sizes of the plastic cups, the depths at which these pitfalls are placed into the soil, the volumes of oil and water in each pitfall, and the same type of oil is used for each experiment.

Materials and Methods

List of All the Equipment

• 1 trowel
• Olive Oil
• Water
• 4 plastic cups: diameter 5cm, depth of 8cm
• 12 small rocks
• 4 large rocks

Diagram Showing the Setup of the Experiment

Method

Area 1:

1. Two areas were chosen where the biodiversity of invertebrates will be investigated; in this case it was the area near the chalet and part of the Eucalyptus plantation.
2. Randomly selected numbers from a calculator were generated and the location of the pitfall was chosen. If there was a feature nearby that would affect the results to a great extent such as a termite or ant hill, the pitfall locations were reselected to maintain accuracy.
3. The cup was filled with 3cm of water and 1 cm of olive oil. A bit of olive oil was spread onto the sides of the cups so that insects did not escape by crawling up the sides of the cup. Olive oil was used because it has a strong smell and will attract most bugs. A sweet substance such as honey was not used because it will make the results inaccurate and attract more specific insects such as ants and bees, mostly.
4. The trowel and the ruler were used to dig an 8cm deep hole so that the cup could fit into the ground. The top of the cup was placed at ground level and not above ground level, as this would prevent any crawling insects from falling into the pitfall.
5. Once the cup was placed into the ground, all gaps surrounding the cup were filled with soil.
6.  3 small rocks were placed on the edges of the cup, as shown in the diagram.
7. One bigger stone was placed over the three small stones. This was done so that if it had rained, the cups would not be flooded; some insects like to go under rocks and stones and also to make sure that the insects can crawl under to rock and into the pitfall. It also prevented some invertebrates from flying out of the pitfalls.
8. The same method as described above was used for Area 2.
9. The pitfalls were left overnight and they were checked every morning at 7am and every evening at 6pm.
10. Once these pitfalls were checked, they were emptied and filled again with water and olive oil and the data (which is the number of invertebrate species and their frequency) was recorded into a table. If some of the invertebrates were found alive then they were gently released back onto the ground.
11. A dichotomous key and an insect identification poster from the internet were used to identify the different species found in the pitfalls.
12. The same process was repeated for 3 consecutive days.
13. The total number and types of invertebrates found in the pitfalls in Area 1 and Area 2 were then compared.

How the Independent Variable Was Varied in the method:

Area 1 was NOT at the Eucalyptus plantation whereas Area 2 WAS at the Eucalyptus plantation. At both areas, randomly chosen numbers from a calculator determined the location of the pitfalls.

How Changes of the Dependent Variable Were Monitored

After checking each pitfall in the morning and evening and recording the results in a table, they were emptied and set up again.

How the Controlled Variables Were Controlled

A ruler was used to measure the depth at which these pitfalls would be submerged.  And the same type of contents (oil and water), and their amounts were used so that insects would not escape from the cups, allowing only one variable to be measured.

How Collection Of Sufficient Relevant Data Was Recorded

Several trials were used, that is, over the course of three days. The data was collected by means of a table showing the data collected for each day.

Results

Data Collection: The following table shows the results obtained, that is, the number of different species and their frequencies, found in each of the pitfalls twice a day, at 7am and at 6pm at Area 1 and Area 2. A key of the different species found at both areas is provided in the table below:

Table 1

KEY:

The table below is a key to the previous table, and information about these invertebrates is given to aid understanding:

Table 2

Species Totals:

Table 3

Area 1

Eucalyptus trees are found to have “peculiar efficacy in repelling mosquitoes”, according to the literature (Glenn W Herrick 2007 page 102).

Comparative Bar Chart , and Pie charts Showing the Total Number and Different types of Species Found at Area 1 and Area 2 Over the Course of 3 Days

Description of the Main Trends and Results Obtained

• Overall, a greater variety of species (biodiversity) were found in Area 2 (12 species found) than Area 1, where only 10 species were found.
• The highest species count at Area 1 was Odorous House Ants, whereas the highest species count was the Driver Ants in Area 2.
• Spiders, beetles, field roaches, crickets, and Pharaoh ants were more common in Area 2.
• Termites, Eucalyptus Long-horned borers, termites, Syrphid flies and lady beetles were found only in Area 2.
• Mosquitoes and houseflies were found ONLY at Area 1.

Data Processing and Presentation

Calculation of the Simpson’s Biodiversity Index

These indices are calculated and are used as the measures of the range and numbers of species in the areas.

Sample calculation: the following formula is used:

d= N(N-1)

    ∑n(n-1)

Where N=total number of all individuals of all species in the area

n=total number of individuals of one species in an area

∑= the sum of

Area 1  

Total number of organisms=90

___________________________90(90-1)_________________________________

[(4x3) + (9x8) + (20x19) + (5x4) + (9x8) + (1x0) + (36x35) + (0x-1) + (1x0) + (0x-1) + (0x-1) + (0x-1) + (5x4) + (7x6)]

d = 8010

      1878

d  = 4.27

Area 2

Total number of organisms=90

___________________________173(173-1)_________________________________

[(11x10) + (0x-1) + (36x35) + (18x17) + (14x13) + (8x7) + (31x30) + (14x13) + (0x-1) + (7x6) + (5x-4) + (5x4) + (23x22) + (1x0)]

d = 29756

      3594

d  = 8.28

The indices calculated above show that 8.28, which is the value of the Simpson’s diversity index for Area 2, is an indicator of greater diversity.

Error Analysis and Uncertainty

(Things that are likely to have an effect on the investigation)

Time of the year could have affected the number of invertebrates found in a certain habitat at a certain time. If it was a season where some invertebrates are not found easily, for example it is hard to find mosquitoes in cold weather; the results of the investigation would be inaccurate. Also, the existence of alien species such as the Eucalyptus trees in Area 2, could have affected the availability of adequate habitats for some invertebrates such as mosquitoes, as these trees contain some insect repelling chemicals. There is also a possibility of some invertebrates having escaped from the pitfall as they were falling in they could have flown out or they could have crawled out of the pitfall, and this could have in turn affected the results of the investigation. It is also possible that the pitfalls at Area 1 could have trapped invertebrates that did not necessarily inhabit that specific area; they could have just been passing, temporarily.

Conclusion 

The results obtained in this experiment, as shown by the tables and the graphs, correspond to the hypothesis, as a greater biodiversity and number of invertebrates were found at Area 2, the Eucalyptus plantation, than Area 1 which was the area surrounding the chalet. The greater the amount of human impact the smaller the number of invertebrates and the smaller the variety of invertebrates will be found in an area. Less invertebrates were found near the chalet, due to clearing of trees and bushes, burning, mowing of lawn and ploughing of land for human-settlement and agricultural purposes, which destroy many invertebrate habitats, such as various plants, trees and holes in the ground. Many invertebrates were probably killed in the process and parts of their food supply were reduced and destroyed. Therefore, with limited availability of food, the population of insects and worms is reduced, and living species of invertebrates are less attracted to the area. However, there were a greater number of mosquitoes, German cockroaches and Odorous ants. This is probably due to the presence of food, eaten by humans, in the chalet which attract these domestic pests. On the other hand, there was a greater biodiversity at the Eucalyptus plantation, as the area was in a more natural state, with greater amounts of plant species that provides nutrients, shelter and protection for a greater number and variety of invertebrates. The Driver Ants were the most common invertebrate found, and this is because this species travels in groups of up to 1000 and they can find their prey more easily, which is insect larvae and sometimes small rodents. Another factor is the sizes of both habitats. The Eucalyptus plantation covered a wider area as compared to the area surrounding the chalet, which was approximately an acre. The quality of the habitat at the Eucalyptus plantation is higher and thus it can support a wider range and number of species.

Evaluation

Evaluation of the Method Used:

The method has proven to be quite a successful one. Considering the small volume of the plastic cup, a significant amount and variety of invertebrates were trapped, which was enough to calculate a relatively accurate and representative biodiversity index for both areas. Perhaps a greater sample of invertebrates could have been collected, by use of a larger cup or tin.

Main Weaknesses in the Method

This was concerning the ethical issues involved in the investigation:

• Every species has the RIGHT TO LIFE whether useful to the human race or not.
• Each area’s wild-life is of cultural importance to the local human population and it is WRONG to destroy it (even though some locals might be destroying it themselves).

Therefore this experiment was not entirely ethical as some bugs were killed in the process.

• The method of using pitfalls to investigate biodiversity is not entirely representative of the whole community, and it could be solely based on chance.
• Some invertebrates are inactive and do not move around much, and so the pitfalls only trap those species that move around a lot such as the ants.

Suggested Improvements that can be Investigated

• A greater number of pitfalls could have been setup in each area to generate a more accurate result.

• A grid pattern when laying pitfalls could be used, after having selected the location randomly, so that a greater depth of knowledge and understanding could be achieved in terms of different species found in relation to the other species found in surrounding pitfalls as well as the location in relation to the distances of the pitfall locations from edges of plantations and buildings. This would also be important in determining.
• An alternative method for collecting invertebrates without having to kill them should be considered due to the ethical reasons mentioned previously.

New Questions that Could be Posed

• Further investigations could be done to determine whether the plant species richness affects the number of invertebrates found in an area.
• If some human activities could be promoting biodiversity, such as the existence of artificially fertilized areas.

References:

ohioline.osu.edu/hyg-fact/2000/2102.html 

greenmethods.com/site/weblog/2007/12/red-ladybug-black-ladybug 

Encarta Encyclopedia

www.ipm.ucdavis.edu/PMG/NE/syrphid_flies.html