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POPULATION ESTIMATION LAB How do you estimate the size of a population? Introduction Measure of population density is essential to many ecological investigations Counting of every individual may not be possible, let alone practical How would you go about estimating the size of a forest community? Transect Line Study - Locate and run transects - Collect data at each sample point - Interpret data How would you go about estimating the size and of a forest community? http://www1.esc.edu/personalstaff/kwatson/fieldwork_site/tree_transects.htm How would you go about estimating the size of an understory community? Quadrants - Lay down a 1 meter squared quad or a hula hoop - Identify and count everything in the quad How would you go about estimating the size of an understory community? http://www.science.oregonstate.edu/bpp/faculty/wilson/Work ersQuad_PR%20(2).jpg How would you go about estimating the size of an animal population? Live Trapping - Lay out transects - Place traps about 10 meters apart using several transect lines typically at dusk - Check traps at dawn - Mark captured animals - Reset the traps and repeat for several days How would you go about estimating the size of an animal population? http://www.stolaf.edu/depts/environmental-studies/courses/es399%20home/es-39905/Projects/Jared's%20Senior%20Seminar%20Research%20Page/htt.htm What do you do with the data? Lincoln-Peterson Index Sample of population (size N) is taken Animals are marked (m) and released back into the population Proportion of population is now marked (m/N) What do you do with the data? Second sample is (size n) is taken later presumably some of the them are already marked (r) Proportion of trapped individuals that are marked (recaptured) in second sample (r/n) is crucial to estimating population size What do you do with the data? Lincoln-Peterson Index Let N= number of animals in the population m= number of animals marked in the first sample and released m/N= proportion of marked animals in the population r= number of recaptured animals in the second sample n= total number of individuals in the second sample Then r/n= proportion of the marked animals in the second sample What do you do with the data? If the sampling is unbiased, then r/n=m/N. To estimate N, rearrange the above equation to yield N=m*n/r What assumptions are made with this method? 1. 2. 3. Sampling is random. Every individual must have an equal probability of capture. The marked animals must be mixed thoroughly and randomly into the population so that the second sample will accurately reflect the population. The population size must not change between the two samples. Mark-Recapture Lab Estimate the size of a bean population through the mark-recapture method and Lincoln-Peterson Index Mark the beans by replacing the captured whitecolored beans with dark-colored beans Repeat the lab using a larger sampler (beaker) Remember to resort your beans at the end!