Sampling Method
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This document provides instructions for students to conduct labs on estimating plant and animal population densities using various methods. For the plant population lab, students will use a quadrat method to sample plant populations and calculate density and frequency. They will record data on number of individuals and presence/absence in quadrats for multiple species. For the animal population lab, students will use a mark-recapture technique to estimate population size of objects like beans by capturing, marking, and recapturing samples. They will record data to calculate a scientific estimate and percent error compared to the actual population.
Sampling Method
- 1. Asian University For Women BIOL/ENVS 3003: Ecology Lab, Fall 2022 Sampling Plant & Animal Population (Lab#2) This content is prepared by Sayed Mohammad Nazim Uddin (Ph.D., Head, Science & Math Program, Associate Professor in Environmental Science) and Syed Mohammad Lokman (Adjunct Faculty, Bioinformatics and Environmental Science), Asian University For Women, Chittagong, Bangladesh. References are cited in between the contents.
- 2. Lab 2.1: Study of plant population density and frequency by quadrat method 1. Aim Our aim is to study plant population density and frequency by the quadrat method. 2. Theory Quadrat Method: Counting all individuals in a population is the most accurate way to determine its size. However, this approach is not usually feasible, especially for large populations or extensive habitats. Scientists usually calculate plant populations with the quadrat method. A quadrat is a square that encloses an area within a habitat. For herbaceous vegetation, a meter square quadrat is normally used. Density: A population is a group of individuals of the same species which inhabit a particular space at a particular time. The number of individuals in a population never remains constant. It may increase or decrease due to many factors like birth rate, death rate and migration. The number of individuals of the species in any unit area at a given time is its population density. The unit area may be as small as 5 square centimeters to as large as 10 square meters, depending on
- 3. the size and nature of the plant community under study. Population density is calculated by counting all the individuals present at a given time in a given space, divided by the number of units of area or space. Population density is calculated as follows: Density = 𝑇𝑜𝑡𝑎𝑙 𝑛𝑜.𝑜𝑓 𝑖𝑛𝑑𝑖𝑣𝑖𝑑𝑢𝑎𝑙𝑠 𝑜𝑓 𝑡ℎ𝑒 𝑠𝑝𝑒𝑐𝑖𝑒𝑠 𝑖𝑛 𝑎𝑙𝑙 𝑡ℎ𝑒 𝑠𝑎𝑚𝑝𝑙𝑖𝑛𝑔 𝑢𝑛𝑖𝑡 (𝑆) 𝑇𝑜𝑡𝑎𝑙 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑠𝑎𝑚𝑝𝑙𝑖𝑛𝑔 𝑢𝑛𝑖𝑡𝑠 𝑠𝑡𝑢𝑑𝑖𝑒𝑑 (𝑄) Frequency: Determining plant population frequency using the quadrat method has become popular primarily because it is relatively simple and objective. Frequency indicates the number of times a plant species is present within a given number of sample quadrats. It is measured by noting the presence of a species in random sample areas which are distributed as widely as possible throughout the area of study. Once analyzed, the sample data enables the scientist to calculate population frequency of the entire population by the following method: %Frequency = 𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑠𝑎𝑚𝑝𝑙𝑖𝑛𝑔 𝑢𝑛𝑖𝑡𝑠 𝑖𝑛 𝑤ℎ𝑖𝑐ℎ 𝑡ℎ𝑒 𝑠𝑝𝑒𝑐𝑖𝑒𝑠 𝑜𝑐𝑐𝑢𝑟𝑠 (𝑇𝑜𝑡𝑎𝑙 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑠𝑎𝑚𝑝𝑙𝑖𝑛𝑔 𝑢𝑛𝑖𝑡𝑠 𝑒𝑚𝑝𝑙𝑜𝑦𝑒𝑑 𝑓𝑜𝑟 𝑡ℎ𝑒 𝑠𝑡𝑢𝑑𝑦)*100 Variations in Plant Distribution: Variation in distribution is caused by several factors like soil conditions, vegetative propagation, quantity and dispersal of seeds, grazing or other biotic activities and predation by insects or diseases. Some species abundantly spread all over the area have a chance of occurring in all the sampling quadrats and therefore, its frequency will be 100. The plants with high frequency are wide in distribution. 3. Learning Outcomes: ● Students understand the term quadrat method. ● Students understand how to calculate plant population density. ● Students understand how to calculate plant population frequency.
- 4. 4. Materials Requires: ● A quadrat frame/Square 5. Lab Procedure 1. Collect your quadrat frame 2. Select the plant species for the study of the population density and frequency 3. Observe the presence of the species A in the first quadrat and record the data in Table.1 for frequency calculations 4. Observe and count the number of the species A present in the first quadrat and record the data in Table.2 for density calculations 5. Similarly check for the presence of the species A in the other quadrats respectively and record the data in the tables. 6. Repeat process 3-5 for species B, C, D, E and record the data in Table 1 & 2. Observations Plant Species Number of individuals in Each quadrats Total Number of Quadrats Studied (Q) Total Number of Individuals (S) Number of quadrats in which the species is present (N) Density D=(S/Q) Percentage Frequency F=N/Q*100 I II III IV V VI VII VIII IX X A 2 0 5 7 10 0 0 0 0 3 10 27 5 2.7 50% B 1 0 4 0 8 0 3 0 0 2 10 20 5 2.0 50% C 4 0 0 3 0 6 0 0 1 2 10 19 5 1.9 50% **The density value thus obtained is then expressed as the number of individuals per unit area. Frequency value indicates the number of times a plant species is present within a given number of sample quadrats.
- 6. Datasheet: Plant Species Number of individuals in Each quadrats Total Number of Quadrats Studied (Q) Total Number of Individuals (S) Number of quadrats in which the species is present (N) Density D=(S/Q) Percentage Frequency F=N/Q*100 I II III IV V VI VII VIII IX X Sp 1 Sp 2 Sp 3 Sp 4 Sp 5 Sp 6 Discussion: Briefly discuss the population density and frequency of Species 1-6 in the sample study area.
- 7. Lab 2.2: Estimating Animal Population 1. Aim To estimate the animal population through group trials. 2. Theory The Mark-Recapture technique is used to estimate the size of a population where it is impractical to count every individual. The basic idea is that you capture a small number of individuals, put a harmless mark on them, and release them back into the population. At a later date, you catch another small group, and record how many have a mark. In a small population, you are more likely to recapture marked individuals, whereas in a large population, you are less likely. 3. Materials 1. Small cups (two for each group) 2. A cup of subjects (e.g., beans/stones/buttons) for each group 3. Marker Pens 4. Printed Data Table 4. Method 1. Get a handful of the subjects from the 1st cup (capture). 2. Mark them all on both sides and count them carefully. Record the data in the table. 3. Take all these subjects off and pour them back into the population (1st cup) 4. Mix them together by using the 2nd cup. 5. After mixing, take a handful of subjects and count all the recaptured marked and unmarked subjects. Record the data in the table. Repeat 4-5 for several times.
- 8. 5. Calculation Part 1: Visual estimate of the number of subjects in the cup:………… Part 2: Number of subjects in your first capture (Ca) all of which you marked:……………….. Part 3: Fill in the following chart with your recapture data: Exercise 2.2: DATA TABLE Recapture Sample Number Number of Recaptured Subjects: Both marked and unmarked (Cr) Number of Recaptured Subjects Marked (Cm) 1 2 3 4 5 6 7 8 9 10 SUM Average 5.1. Scientific Estimate Scientific Estimate = = ………. 𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑆𝑢𝑏𝑗𝑒𝑐𝑡𝑠 𝑖𝑛 𝑦𝑜𝑢𝑟 𝑓𝑖𝑟𝑠𝑡 𝑐𝑎𝑝𝑡𝑢𝑟𝑒 (𝐶𝑎) 𝐴𝑣𝑒𝑟𝑎𝑔𝑒 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑚𝑎𝑟𝑘𝑒𝑑 𝑠𝑢𝑏𝑗𝑒𝑐𝑡𝑠 𝑓𝑟𝑜𝑚 𝑡ℎ𝑒 𝑟𝑒𝑐𝑎𝑝𝑡𝑢𝑟𝑒 𝑠𝑎𝑚𝑝𝑙𝑒 (𝐶𝑚) 𝐴𝑣𝑒𝑟𝑎𝑔𝑒 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑠𝑢𝑏𝑗𝑒𝑐𝑡𝑠 𝑓𝑟𝑜𝑚 𝑟𝑒𝑐𝑎𝑝𝑡𝑢𝑟𝑒 𝑠𝑎𝑚𝑝𝑙𝑒𝑠 (𝐶𝑟) ( ) 5. 2. Percent Error 1. Count the actual number of subjects in the 1st cup: ….. 2. Determine the percent error of your scientific estimate using the following formula: % error = *100 =..................... 𝑆𝑐𝑖𝑒𝑛𝑡𝑖𝑓𝑖𝑐 𝐸𝑠𝑡𝑖𝑚𝑎𝑡𝑒 – 𝐴𝑐𝑡𝑢𝑎𝑙 𝑁𝑢𝑚𝑏𝑒𝑟 𝐴𝑐𝑡𝑢𝑎𝑙 𝑁𝑢𝑚𝑏𝑒𝑟 ( )