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Mark Rec103

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Biology 103 A Method of Population Estimation: Mark & Recapture ! ecti#es: 1. Learn one method used by wildlife biologists to estimate population size of wild animals. 2. Learn how sampling size effects accuracy and standard error of estimates. 3. Use the mark-recapture method to estimate the number of coins in a jar. $% $ntroduction o understand how different physical or biological factors influence the distribution or abundance of species! we usually need to measure changes in population
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  Biology 103 A Method of Population Estimation: Mark & Recapture ! ecti#es: 1.Learn one method used by wildlife biologists to estimate population size of wild animals. 2.Learn how sampling size effects accuracy and standard error of estimates. 3.Use the mark-recapture method to estimate the number of coins in a jar. $% $ntroduction o understand how different physical or biological factors influence the distribution or abundance of species! we usually need to measure changes in population abundances o er space or time. #cologists interested in $uestions about populations and communities fre$uently face a ery basic $uestion% how best to estimate the size of a population of organisms in the field& 'owe er! it usually is not possible to obtain a complete count or census of a natural population of animals (and it is often difficult e en for plants)*. +or this reason! ecologists generally ha e to rely on some kind of estimate of abundance or density. , ariety of methods eist to do the  job the utility of each aries depending on such factors as the type of organism! the habitat in which the  population occurs! and the time and e$uipment a ailable.he methods ecologists use ary in their le el of precision and difficulty of application. ,t one etreme is a complete census of indi idually identifiable organisms. his approach might in ol e tagging all trees in a forest plot! or marking all the animals of a species li ing in an area at a particular time. echni$ues for indi idually identifying animals include% ã /ompiling a catalog of photographs or drawings that show uni$ue markings of indi iduals (e.g.! fin shape and markings whales spot patterns on ,frican wild dogs whisker patterns in lions facialepressions in primates* ã agging indi iduals with markers isible from a distance or in the hand (e.g.! numbered metal leg bandson birds colored plastic leg bands in uni$ue patterns on birds strings of beads around the necks of small primates wing tags on bats*. ,t the other etreme are 0$uick  dirty methods that gi e crude estimates of abundance. #amples include counting all birds sighted along a roadside route one tra els by car counting the number of monarch  butterflies passing a point such as /ape ay during migration counting the number of bird songs one hears during a morning in the spring scanning aerial photographs of wildebeest herds on the ,frican plains or counting animal tracks along a trail.4ne may count the number of singing males of a species of bird in a gi en community or defined area and thenestimate the size of the breeding population by assuming that for e ery male there is one female. 4r one may count the indi iduals in a sample area and then etrapolate to the larger area in which the whole population is assumed to li e. 5ecause each method has different assumptions and hence! different strengths and weaknesses! it is recommended (though rarely done* that at least two estimation methods be used and compared in any population study., ariety of methods for estimating population size fall between the two etremes outlined abo e. hese methods in ol e marking a subset of a population! followed by later counts of the relati e numbers of marked and unmarked indi iduals. his type of method is more precise than a crude census in which no organisms are marked at all! but takes less time and epense than does an ehausti e marking program.  he Mark and Recapture echni'ue 5y far the most popular way to measure the size of a population is called the ark and 6ecapture echni$ue. his techni$ue is commonly used by fish and wildlife managers to estimate population sizes before fishing or hunting seasons. he mark and recapture method in ol es marking a number of indi iduals in a natural population! returning them to that population! and subse$uently recapturing some of them as a basis for estimating the size of the population at the time of marking and release. his procedure was first used by /.7.8. 9etersen in studies of marine fishes and +./. Lincoln in studies of waterfowl populations! and is often referred to as the Lincoln :nde or the 9etersen :nde. :t is based on the principle that if a proportion of the population was marked in some way! returned to the srcinal population and then! after complete miing! a second sample was taken! the proportion of marked indi iduals in the second sample would be the same as was marked initially in the total population. hat is! R (marked recaptures* M (marked initially*  ;;;;;;;;;;;<  ;;;;;;;;;;;;   (total in second sample* ( (total pop. size* 5y rearrangement we can estimate the population size! =! to be! M)( < ;;;  R  +or eample! suppose you took 2>> mice out of a forest ha ing an unknown number of mice! put leg bands on them! return them to the forest and let them mi thoroughly. :f you then take 2?> mice from the forest and find ?> of them to be ha e leg bands! then M * +00 !  * +,0 ! R * ,0 ! and the unknown total number of mice (=* could be estimated as% ( * M)-R * .+00/.+,0/-,0 * 1000 mice @ample problem%, pest control technician captures and applies ear tags to 23 brown rats! which he then releases. , week later he traps 2A brown rats! 11 of which ha e ear tags. Bhat is the estimate of the total population of brown rats& Assumptions % he accuracy of this mark-recapture method rests on a number of assumptions being met. Assumption 1 . Curing the inter al between the preliminary marking period and the subse$uent recapture    period! nothing has happened to upset the proportions of marked to unmarked animals (that is! no new indi iduals were born or immigrated into the population! and none died or emigrated*. ,nother way to state this assumption is that the population is assumed to be DclosedD. ,n eception is when there are e$ual  proportions of deaths or emigrants for marked and unmarked indi iduals during the sampling period. :f deaths occur in this manner the proportions of marked to unmarked will not change and thus we can still estimate the population. =otice the same cannot hold true for births since a proportionate number of indi iduals will not be born with marks on them. 5irths can still occur and an accurate estimate can still be made only if an e$ual number of unmarked indi iduals lea e (or die* and are born. his means that no marked indi iduals can lea e! which would be highly unlikely.   =otice that inherent in this assumption is that the marking of the indi iduals has no effect on their sur i al. his is often the most difficult assumption to meet since the mark may make the indi idual more noticeableto predators or may slow them down! such that more marked indi iduals die than unmarked between the sampling periods.Eou should also be aware that the length of the sampling period is ery important. he shorter the time inter al between marking and recapturing indi iduals reduces the likelihood that this assumption will be iolated. he longer the time inter al the greater the chance that some indi iduals will die! emigrate! immigrate or e en be born and hence become an DopenD population. Assumption + . he chance for each indi idual in the population to be caught are e$ual and constant for both theinitial marking period and the recapture period. hat is! marked indi iduals must not become either easier or more difficult to catch. arking an indi idual does not make them more or less likely to be recaptured relati e to unmarked indi iduals. +urthermore! there cannot be something uni$ue about those animals that were initially marked that make them more conspicuous. :f only males are captured in the traps because females are busy incubating eggs or feeding! then males may be more likely to be recaptured. 'ence the  population estimate would only be appropriate for those animals with that uni$ue beha ior that make them easier to capture (i.e. males*.,nother problem deals with Ftrap shyF or Ftrap happyF indi iduals. @ome techni$ues for capturing and marking animals can ha e a dramatic effect on the animal. 0rap shy animals $uickly learn to a oid those traps or that area where the capture occurred making them less like to be recaptured. he opposite can also occur! especially if the trapping method uses bait. , 0trap happy indi idual is lured into a trap with food and is then marked. Later during the recapture period the animal may recall that these traps had rewards (food* and that other than a little decoration (the mark* it made out pretty good. herefore it becomes 0trap happy and is more likely to be captured in the trap compared to unmarked indi iduals who ha e not eperienced the rewards.,lso notice that there cannot be any changes in beha ior among indi iduals that may affect capture  probabilities. +or eample! in some species there are different times of peak acti ity for different classes in the population. ,dult males may be most acti e in the morning. 7u enile males and females may be most acti e midday! and adult female may be most acti e in the afternoon. :f you mark indi iduals in the morning you will capture and mark mostly males. 5ut if you perform your recapture sample at midday or the afternoon! you will capture mostly unmarked ju eniles or females! respecti ely. ,gain! you should realize that the length of time between the sampling periods plays an important role in whether this assumption is iolated. Assumption 3 . @ufficient time must be allowed between the initial marking period and the recapture period for all marked indi iduals to be randomly dispersed throughout the population (so that assumption 2 abo e holds*. 'owe er! the time period must not be so long that ,ssumption 1 breaks down. :f marked animals failed to disperse from the sampling area! or if they tend to aggregate in groups! there is a higher probabilitythat they will be recaptured relati e to unmarked indi iduals (or not depending on where they aggregate*. Assumption % ,nimals do not lose their marks. his is an important factor for animals that shed or molt as   they grow or as they respond to seasonal factors.,ll these assumptions must be considered ery carefully and play a strong role in the techni$ues used to  perform the study. , certain method of trapping may iolate one assumption while another trapping method may iolate another assumption. 'a ing too short of a time inter al between sampling may lead to the iolations of one assumption (which one(s*&* while an inter al that is too long will iolate others (which one(s*&*.  /learly the decisions the researcher must make during such a study re$uire an etensi e knowledge of the natural history of the organism. Co beha ioral patterns change o er the day& Bhen do they breed& Bhen does most of their mortality occur& Bhat are their predators& 'ow $uickly can they mo e& ,re they territorial& Guestions like these must be answered before the eperiment is designed and performed so that a minimum of iolations to the assumptions are made. $$% Methods  Eour goal is to estimate a population size using the mark-recapture method. Eou will use an   unknown amount of beans as your model population.#ach pair of students needs these materials%1-H>> ml 5eaker which represents the habitat to be sampled1-small 5eaker (sampling beaker*1-I>> ml 5eaker with a known number of white beans 1-I>> ml 5eaker with colored beans (marked indi iduals*1-I>> ml beaker (empty! to hold beans remo ed from the population* Effort 1: 1. 4btain a population of white beans! a large habitat beaker! colored beans! and one small beaker. he white beans will represent the population to be sampled. 2. Marking % Using the small beaker as a JtrapK! push through the white bean population once! filling the trap   with beans to the 1> ml line. /ount the number of white beans caught and for each white bean caught! substitute a colored bean and record that number as% (um!er marked * M%  (#.g.! if you JtrappedK 23 white  beans with your sampling beaker you would put 23 colored beans into the srcinal population*. 3. horoughly mi the marked and unmarked bean population. (Bhich assumption does this fulfill&* I. Recapturing % =ow sweep through the mied bean population with the trap once! filling the trap to the 1>   ml line. :f you reco ered at least one colored bean with this sweep! record the number of marked beans ( recaptures * as R  . 6ecord the total number of beans caught as  ! ( i.e. marked 2 unmarked *. ?.  =ow calculate the bean population size using the formula ( * M)-R    Effort +: 6epeat steps 2! 3! I! and ?! but this time fill the trap to the 2> ml line at 2 and I. hat is! you will be doubling your sampling effort. Effort 3 %6epeat steps 2! 3! I! and ?! but this time fill the trap to the 3> ml line at 2 and I. ,gain! you are increasing your sampling effort.

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Jul 22, 2017

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