BIO 1104L - Nematode Ecology Lab Report

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Feb 20, 2024

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Hafsah Mohammed BIO 1104L CRN: 94218 Nematode Ecology Experiment Introduction: Population ecology is the study of factors that affect population growth, rates of survival and reproduction, death rates, and why the population changes over time (Dotson 2019). A population is all of one species found in a specific location. Ecologists study population ecology to better understand what is happening to the population and species over time, studying the data can help to protect endangered species. Population growth is the change in the number of individuals of the species over a specific period of time. Population growth is controlled by the birth rate and death rate, which is controlled by other factors, such as predators, weather, lack of food, etc. (Dotson 2019). Population is stable when birth rates and death rates are equal, if birth rates are high then population skyrockets, whereas, if death rates are high, the population falls. Nematodes are from the phylum Nematoda, there are over 25,000 species in this phylum, and only a few thousand have been identified (UC Riverside). Nematodes are multicellular worms and are among the biggest population of animals on earth. Just a handful of soil can have thousands of nematodes. Nematodes are usually found in soil, and some are visible, but most are typically camouflaged because they are clear (Lochamy & Summerill, 176). Nematodes can also be found in freshwater marine habitats, but because of the complex taxonomy and small size, they have not received a lot of time and attention (Dodds, 2002). Nematodes are usually burrowing in the soil. In. order to survive nematodes need water and food. The water they need is in the soil, if there is moisture in the soil, they will be fine. For food, nematodes eat microscopic or decomposing organic matter, called humus (Lochamy & Summerill, 177). Correlation is a statistical measure that describes how two variables are linearly related (Hayes 2021). When two factors are correlated, it means that a change in one factor will cause a change in the other factor. There are three different types of correlation: direct, inverse, and no correlation. Direct correlation is also known as positive correlation, and it happens when both variables move in the same direction. If one variable increases, so does the other one. Inverse correlation, also known as negative correlation, and this happens when the variables move in opposite directions. If one variable increases, the other decreases. No correlation, or zero correlation, means the variables have no effect on one another and there is no relationship between them (McLeod 2020). Once the variables are plotted on the graph, we have to see if the correlation is strong or not, this is done through the trend line, which is a straight line that runs closest to all the points possible (Lochamy & Summerill, 178). In order to see if the correlation is strong or not, each line is marked with a number called R^2. R^2 is a number between 0 and 1, the closer it is to 1, the stronger the correlation, if it is closer to 0, the weaker the correlation (Lochamy & Summerill, 178).

Objective: The purpose of this study is to see how many nematodes are in a soil sample, based on water percentage, soil density, and organic material. Hypothesis: - The denser the soil is the more nematodes there will be - The higher the water percentage is the more nematodes there will be in the soil. - There will be more nematodes if the organic matter amount is high in the soil sample. The independent variables of this experiment are the soil density, water percentage, and humus in the soil sample. The dependent variable of this experiment is how many nematodes are found in the soil sample. The control variables of this experiment are the height of the soil (3cm) and the amount of water added to the funnel and lack of water in the dry reference sample. Results: Table 1 R² = 0.1061 0 10 20 30 40 50 60 0 0.1 0.2 0.3 0.4 0.5 Average Number of Nematodes Organic Matter (540 nm) Organic Matter vs. Average Number of Nematodes

Table 2 Table 3 The graphs above compare the results of each group in the class, the organic matter vs. number of nematodes, soil density vs. the number of nematodes, and water percentage vs. the number of nematodes in the soil. Each graph presented a trend line. All three tables have a trendline going down, having a negative correlation. R² = 0.1918 0 10 20 30 40 50 60 0 5 10 15 20 25 30 35 Average Number of Nematodes Soil Density Soil Density vs. Average Number of Nematodes R² = 0.1063 0 10 20 30 40 50 60 0.00% 5.00% 10.00% 15.00% 20.00% 25.00% 30.00% Average Number of Nematodes Water Percentage Water Percentage vs. Average Number of Nematodes

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In table 1, which compares organic matter vs. number of nematodes, we can see that the R 2 is 0.11, which means the correlation is weak between the two sets of data points. In table 2, which compares soil density vs. number of nematodes, the R 2 is 0.20, which means the correlation is weak between the two sets of data points, but it is stronger than table 1’s results. In table 3, which compares water percentage vs. number of nematodes, the R 2 is also 0.11, just like table 1. There is a weak correlation between the two sets of data points. Discussion: Our first hypothesis was that the denser the soil is, the more nematodes we will find. The data we got, however, proved that wrong. There isn’t a strong correlation between the number of nematodes and soil density for any of the groups. We had 10 nematodes in our soil sample, and our soil density was 13.67 grams, compare to group 3, which had 56 nematodes, yet their soil density was only 12.52. Our second hypothesis was that the higher the water percentage was, the more nematodes we will find in the soil sample. This hypothesis was somewhat true, while some groups did have a high-water percentage and more nematodes, some groups had a high-water percentage but did not find a lot of nematodes in their soil sample. Our group had 10 nematodes and our water percentage was 24.5%. Our third hypothesis was that the higher amount of organic matter, humus, in the soil sample, the more nematodes we will find. This hypothesis was proven true by the data we collected. The more organic matter there was in the soil sample, the more nematodes were found. This was the case for all groups except group 2, who found 6 nematodes but had an organic matter content of 0.43. As mentioned in the introduction, research shows nematodes can live in soil if they have food and water available. The results from our experiment prove that even in a small soil sample, nematodes can continue to live if there is moisture and organic matter present in the soil. All three tables above, have a negative correlation, the line is going down. All the data is scattered around the plot, so there is no correlation between all the data points. This is understandable as we all collected soil from different places, so each group had a different soil density, organic matter, and water percentage. Our group did not have any issues with this experiment. The experiment was straightforward, we collected the soil, weighed it, and left it for the week, and came back a week later and checked on it. If we were to do this experiment again, I think we will get better results if we gather our soil sample from another location. Group 3 collected their soil sample close to the trees and they got over 50 nematodes, whereas we collected right at the start of the soil and end of the cement. Our group only got 10 nematodes, which also proves that location matters. If the soil is easy to burrow in, more nematodes will live there, if the soil is harder to move around in, like the soil right by the cement, not as many nematodes will live there because of the inability to burrow properly.

Works Cited Dotson, J. Dianne. “Ecological Research Methods: Observing, Experimenting & Modeling.” Sciencing , 8 Jan. 2020, https://sciencing.com/ecological-research-methods-observing- experimenting-modeling-13719222.html Hayes, Adam. “What Is Correlation in Finance?” Investopedia , Investopedia, 3 Nov. 2021, https://www.investopedia.com/terms/c/correlation.asp Holt, Robert D. “Population Ecology.” Access Science , McGraw-Hill Education, 1 Jan. 1970, https://www.accessscience.com/content/population-ecology/538150 Lochamy, J. Summerill C. “Introductory Biology: Laboratory Manual” Hayden-McNeil Lab Solutions, 2020. Mcleod, Saul. “Correlation Definitions, Examples & Interpretation.” Correlation Definitions, Examples & Interpretation | Simply Psychology , https://www.simplypsychology.org/correlation.html “What Are Nematodes?” Department of Nematology , 11 Jan. 2020, https://nematology.ucr.edu/about/what-are-nematodes

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