- Lab Exercise 3b Indoor Capture Mark Recapture Exercise Research Question How Do Population Estimates Using Mark Recaptu 1 (112.03 KiB) Viewed 56 times
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Lab Exercise 3B: Indoor Capture-Mark-Recapture Exercise Research Question How do population estimates using mark-recapture techniques compare to the true population size? Preparation Mark-recapture involves marking a set number of organisms, releasing them back into the population where they mix with unmarked individuals, and then doing a second collecting visit. Since mark-recapture typically requires a substantial time between marking and recapturing (at least 24 hours, and generally longer), we will simulate the process using the incredibly non-mobile items (rolls of paper/beans/ball etc) in place of a mobile animal. Materials (per laboratory team) Beaker or container to hold rolls of paper/beans/balls etc Rolls of paper/beans/balls etc Sampling container (such as a box/beaker/centrifuge tube) Marker 1. Obtain a container and add samples (papers/beansballs to it. 2. Obtain a sampler (a box or centrifuge tube) and collect a sample of papers/beans/balls by filling the sampler to the top. Count and record the number collected and mark each collected samples with a marker. After marking, return the samples to the population and thoroughly mix the samples by shaking the container. 3. Draw out a second sample. Record the number of marked and unmarked samples, but do not return this to the population just yet. You will use these numbers to estimate population sising the Lincoln- Peterson index. 4. Now mark each unmarked sample and return this sample to the population, thoroughly mix, and then take a third sample. Again, count the number of marked and unmarked samples, mark the unmarked samples and return the sample to the samples population. 5. Take a fourth and final sample, and count marked and unmarked samples. Now you have the data necessary to estimate population size using the Schnabel index.
Data Analysis: Population Size Estimate 1. Enter your data in the table below. Table 3.3 Mark-Recapture Data i C₁ 1 2 3 4 72 Lincoln-Peterson Index: 2. Using the Lincoln-Peterson index, calculate the number of pinto beans in the population (N). Show your calculations. N = population size estimate M= marked individuals released S = size of second sample R= marked animals recaptured N= ΣM.C 1-1 M-S R 3. Using the Schnabel index, calculate the number of pinto beans in the population (N). Show your calculations. 1-1 R₁ R₁ New marked M₁ Discussion How do your estimates compare to the true population size? If your estimated values differ from the true value, why do you think this might have occurred? Did the Schnabel index give you a better estimate of the actual population size than did the Lincoln- Peterson index? Why? Exercise 3.B. Estimating Population Size: Mark-Recapture
3.0 RESULTS į 1 2 3 4 Ci 18 27 26 24 R₁ 34 29 20 33 New Marked 0 11 5 16 M₁ 5 16 11 33
Estimated population size is: where N = M = C = R = N = MX C R Estimate of total population size Total number of animals captured and marked on the first visit Total number of animals captured on the second visit Number of animals captured on the first visit that were then recaptured on the second visit
Example: Some of the individuals in this second sample will have been marked during the initial visit and are now known as recaptures. Other animals captured during the second visit will not have been captured during the first visit to the study area. These unmarked animals usually are given a tag or band Population size can be estimated from as few as two visits to the study area. Commonly, more than two visits are made, particularly if estimates of survival or movement are desired. Regardless of the total number of visits, the researcher simply records the date of each capture of each individual. The "capture histories" generated are analyzed mathematically to estimate population size, survival, or movement. 15 The Lincoln-Petersen method can be used to estimate population size if only two visits are made to the study area. This method assumes that the study population is "closed." In other words, the two visits to the study area are close enough in time so that no individuals die, are born, move into the study area (immigrate) or move out of the study area (emigrate) between visits. The model also assumes that no marks fall off animals between visits to the field site by the researcher, and that the researcher correctly records all marks. N = Sample calculation A biologist wants to estimate the size of a population of turtles in a lake. She captures 10 turtles on her first visit to the lake, and marks their backs with paint. A week later she returns to the lake and captures 15 turtles. Five of these 15 turtles have paint on their backs, indicating that they are recaptured animals. MX C R Capture-recapture techniques 10 x 15 5 = 30 In this example, the Lincoln-Petersen Method estimates that there are 30 turtles in the lake.