Counting of Animal Population - Lab Report Example

Counting of Animal population Counting of animals population Introduction For effective management of population about the density and size, the knowledge about their population is vital. Making of an estimate of the population size and density is important because the organisms are many in terms of community and habitat in the ecosystem to be counted all. For effective method of data collection and calculation techniques, Mark and Recapture method with three different calculation methods is used. The method involves capturing organisms, marking them, releasing them, and then resampling to obtain the fraction of the marked individuals to estimate population size (Dupuis et al., 2012). The method also provides ancillary information about the birth of an organism, movement and death rates. The method is used in both open and closed population whereby in the public system, the organisms can change both in size, migration and number considerably, and the closed system there is no major change in the above parameters (White& Burnham, 1999). Aim To calculate the estimates of population size of blowfly maggots, Calliphora sp in a sawdust filled bowl as a model habitat Materials and methods Materials The materials used included sawdust-filled bowls containing a known number of plain uncoloured maggots. In addition, a number of dark red, bronze and pink coloured maggots were used. Methodology In the first sample, a 50ml beaker was used to fish for maggots through the sawdust by not trawling. The number of caught maggots was then counted before returning them to pool container. The dark red maggots were then replaced by the removed ones and termed as marked organisms before placing them o habitat surface to take the second sample after they got buried in the dust. In the second sample, the same step of the first sample was followed, and uncoloured organisms caught recorded as first time and how many marked dark red maggots were previously caught. The bronze maggots were then used to replace the caught ones in the second time and allowed to bury in the dust. In the third sample, the uncoloured organism in the first sample was recorded, and the second sample organisms that were dark red and the bronze maggots caught in the third sample. The untagged uncoloured maggots were then replaced by dark red ones that were then replaced by the bronze maggots. The green maggots were then replaced by bronze ones caught in the third time. The same procedure was then used in seven different samples. Results Table 1: Number of maggots caught at each sample No. of samples Total maggots caught(a+b+c+d) 1st catch replaced with dark red (a) 2nd catch replaced with bronze (b) 3rd catch replaced with pink (c) 3rd catch, green (d) Previously marked (b+c+d) Cumulative total caught maggots (e) 1 2 2 0 0 0 0 2 2 5 5 0 0 0 0 7 3 3 2 1 0 0 1 12 4 5 2 3 0 0 3 14 5 2 2 0 0 0 0 16 6 1 0 1 0 0 0 16 7 3 2 0 1 0 0 18 8 4 1 2 0 1 3 19 9 6 4 1 1 0 2 23 10 4 1 2 1 0 3 24 Table 2: Cumulative numbers of maggots in every sample Sample Ci (number of animals caught in sample) Mi (previously marked maggots in cumulative samples) Ri (caught maggots that are coloured) Total value of (Mi X Ci) 1 2 2 2 4 2 5 7 5 35 3 3 12 4 36 4 5 14 8 70 5 2 16 2 32 6 1 16 1 16 7 3 18 3 54 8 4 19 7 76 9 6 23 8 138 10 4 24 7 96 Calculations and discussion The data was then calculated using different methods. Lincoln-Petersen method It involved a single episode for marking and recapturing of the maggots and data analysed as follows. M, as number of maggots marked in the first sample C, as total number of maggots captured in second sample R, as number of maggots in second sample that are marked Thus, N, which is the size of population at time of marking, is given by; N= CM/R = (557/47) = 11.851 The main limitation of the method is that it overestimates the actual population. Therefore, to reduce the biasness, the suggested method by Bailey is by, N= M (C + 1) / R+ 1, N therefore = [151(35+1)/ 47+1] = 113.25. Averagely per sample; (113.25/10) = 11.325 SE (N) = [M2 (C+1) (C-R)] [(R+1)2 (R+2)], = =87.2487 Average per sample therefore, (87.2487/ 10), = 8.72487 Confidence level that is the range of values expected to include the true population size a given percentage of time can be calculated as to produce two values. Confidence interval = ] Lower 95% confidence limit on N = N + (M/ large value) and vice versa. Lower confidence limit on N, = (11.325+ (15.1/2.1844)) = 18.238 Upper confidence limit on N, = (11.325 – (15.1/2.1844) = 4.4123 Confidence intervals are an essential guide to the precision of the estimates. The population estimate should not always have a very wide confidence interval. The method of Lincoln-Peterson has several assumptions that are; all organisms have the same chance of getting caught in the first sample and marked individuals in the population mix randomly. Additionally, marked organisms have the same probability of survival as unmarked ones and when the population is closed, N is constant and, therefore, birth is equal to death that is equal to immigration and emigration (Minta & Maugel, 1989). Additionally, marking individuals does not affect catchability of organisms since marked organisms are not easy and hard to recapture. Moreover, organisms do not lose their marks between the two sampling periods, and all marks are reported on the discovery in the second sample. Lastly, recapture rates are high enough to support an accurate estimate as it overestimates population size (Adams, 1951). Schnabel’s method generally extends the Lincoln-Peterson since the assumption that is violated since it is hard to get enough recaptures in large populations and thus, the Schnabel’s method is applied. The formula, Where, Mi is the total number of previously marked maggots at time I, Ci is the total number of maggots caught at time I, and the Ri is the number of marked animals caught at time i. From the equation, , N = (557/47) =11.851. Thus, the total number of maggots from the method above is approximately 11. In Chaos method, it describes the capture frequencies. This is analogous to estimating the number of species represented by only one individual to the maximum number obtained. It is usually solved by using a logarithmic, geometric or hypergeometric series (Chao 1987). The formula, N Chao = N Obs + (a2 /2b), where N Obs is the total number of maggots caught, a is the number of maggots caught once and b is the maggots caught exactly twice. N = 35 + (352/24) [35+ 51.042] = 86.042, = 8.6042. In conclusion, therefore, the different types of methods are used to estimate the population of organisms in a given population. The large number of the organism makes it difficult to obtain the actual size of the population. The capture-recapture method, the Lincoln-Peterson and Chaos method are used for population estimation. The results are precise and provide ranges in the different types of methods used. References Adams, L. 1951. Confidence limits for the Petersen or Lincoln Index used in animal population studies. The Journal of Wildlife Management, pp.13-19. Chao, A. 1987. Estimating the population size for capture-recapture data with unequal catchability. Biometrics, pp.783-791. Dupuis, P, Kaynar, B, Ridder, A, Rubinstein, R, & Vaisman, R 2012, Counting with Combined Splitting and Capture–Recapture Methods, Stochastic Models, 28, 3, pp. 478-502 Minta, S., & Mangel, M. 1989. A simple population estimate based on simulation for capture- recapture and capture-resight data. Ecology, pp.1738-1751. White, G. C., & Burnham, K. P. 1999. Program MARK: survival estimation from populations of marked animals. Bird study, 46(S1), S120-S139. Read More