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by: Henri Kshlerin
Henri Kshlerin
GPA 3.54


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Class Notes
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This 3 page Class Notes was uploaded by Henri Kshlerin on Tuesday October 20, 2015. The Class Notes belongs to BIOL541 at San Diego State University taught by T.Anderson in Fall. Since its upload, it has received 20 views. For similar materials see /class/225256/biol541-san-diego-state-university in Biological Sciences at San Diego State University.

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Date Created: 10/20/15
Biol 541 7 Ecology of Fishes and Fisheries Biology Fall 2003 METHODS OF ESTIMATING POPULATION SIZE MARK RECAPTURE The most fundamental task in population ecology is to determine or estimate population size One way to estimate the size of a population is to capture and mark individuals from the population release them and then resample to see what fraction of individuals carry marks Various techniques with accompanying equations are then used to approximate population size For this lab exercise we will be illustrating two techniques by running a simulation and capturing quotorganismsquot and marking them returning them to the quotpopulationquot and subsequently resampling the poulation We will use two methods for estimating population size 1 the Petersen Method and 2 the Modi ed Schnabel Method Both methods are useful when sampling closed populations those populations that do not change in size at all or very much during the study period due to births deaths immigrationor emigration Open populations are those that can uctuate in size and composition due to the same parameters especially for animals that are mobile emigration and immigration Petersen Method This is a simple markandrecapture method based on a single episode of marking animals and a second single episode of recapturing individuals Our basic procedure will be to rst collect and mark a number of individuals from our quotegg rejectquot population and then resampling the population and tallying the number of marked and unmarked eggs We will be using an quotorganismquot that has six color morphs and three sizes Three measures are needed to estimate N population size M the number of individuals marked in the first sample C total number of individuals captured in 2nd sample R number of individuals in 2nd sample that are marked These are placed into the following equation N CM R or if R is greater than 7 N M CC1 R 1 1 Assumptions of Petersen Method 1 The population is quotclosedquot so N is constant 2 All animals have the same chance of getting caught in the first sample 3 Marking individuals does not affect their catchability 4 Animals do not lose marks between the two sampling periods 5 All marks are reported on discovery in the second sample Modi ed Schnabel Method This method is merely an extension of the Petersen Method but uses multiple sampling to derive an estimate of population size For each sample we need the following measures Ct total number of individuals captured in sample I Rt number of individuals already marked in sample I Ut number of individuals newly marked and released in sample I Mt total number of individuals marked in population at sample I The following equation is used based on a modification by the Schumacher and Eschmeyer Method N th2 RtMt Assumptions for M odz39fzed Schnabel Method are the same as for the Petersen Method Problem Sets 1 Calculate estimated total population size based on the Petersen Method 2 Using the Petersen Method calculate separate estimates for each size class of the population 3 Calculate estimated total population size based on the Modi ed Schnabel Method 4 Using the Modi ed Schnabel Method calculate separate estimates for each size class of the population 5 Calculate estimated population size by color for both the Petersen and Modi ed Schnabel Methods 6 What statements can you make regarding potential biases or differential estimates of population size based on color and size 7 Assess which of the above methods is more accurate relative to the true population size calculate for total population size population size by size class and population size by color using the following equation Calculating Accuracy A i 100 Estimated pop size minus true pop size True pop size Biol 541 7 Ecology of Fishes and Fisheries Biology Fall 2003 True population size Colo r Green Orange Yellow Pink Blue Purple Size Small 15 15 15 16 16 14 Medium 24 24 24 24 24 23 Large 8 7 7 8 8 8 Total 280


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