Community Sampling. Lab Exercise 43. Objectives. Introduction

Transcription

1 Lab Exercise Community Sampling Objectives - To experience the mark and recapture method used to sample populations within communities. Introduction When studying a community or population, often one of the first issues addressed is to quantify the kinds and numbers of individuals in the community. Since it is rarely practical if even possible to physically count each individual, a wide variety of sampling methods have been developed to provide estimates of these values. This simulation models one such method commonly used to quantify the population size of small animals To begin this simulation, go to the Ecology section of the BiologyOne DVD and select Community Sampling. After the introductory screen, click on the forward arrow to begin this simulation. 1

2 Activity.1 General Procedure For many animal species it is impractical to attempt to count every individual. Consequently, a number of methods have been developed to sample a population to make population estimates. One such method is the mark and recapture technique. From the trapping data, the size of the population is estimated from the equation: Σ M N i = i C i Σ R i The mark and recapture method simulated in this exercise allows you can trap individuals from the population. These are then marked and released back to the population. During subsequent trapping in the population, the number of trapped individual that were previously trapped is recorded as well as the number of individuals trapped for the first time. Any unmarked individuals are then marked and released into the population. Consequently, the total number of marked individuals increases as sampling continues. Where N i is the estimated size of the population for the ith trapping, M i is the total number of marked individuals in the population up to the ith trapping, C i is the total number of individuals trapped in the ith trapping and R i is the number of marked individuals recaptured. Σ stands for the the sum of. So in this equation, the numerator is the sum of M 1 C 1 + M 2 C etc. and the denominator is the sum of all R values. 2

3 Activity.2 Sample Collection in the Simulation In this simulation, you give the actual population size in the upper right corner of the screen. You will be trapping individual from this population to see how well this method can estimate the population size. The organisms of this population are red dots that move randomly through the habitat shown in the middle of the screen. In the habitat area you will see ten traps for these organisms. Before trapping you can move these traps to any location in the habitat by clicking on them and dragging them with the mouse key down. When you are ready to begin trapping, click on the blue button in the lower left corner. When you want to stop trapping, click on that blue button again. The numbers of marked and recaptured individual will be displayed as well as the estimated size of the population. Exercise 1 In the first exercise in the simulation, you should trap individuals for ten trapping cycles. Between each trapping episode, move the traps to a different location in the habitat area. Record and plot the estimated population size for these trappings in the Results Section. Exercise 2 In the second exercise for this simulation, before your first trapping, move the traps to the location you would like them. Then, trap individuals for a total of ten trapping cycles without moving the traps. Record and plot the estimated population size for these trappings in the Results Section. Does moving the traps in influence this method s accuracy to estimate the population size? Screen for Mark & Recapture Simulation traps 3

4 Lab Exercise Name Results Section Activity.2 Sample Collection in the Simulation Exercise 1: Moving Traps Actual Population Size: Estimated Population Size After 1st trapping: After 6th trapping: After 2nd trapping: After 7th trapping: After 3rd trapping: After 8th trapping: After 4th trapping: After 9th trapping: After 5th trapping: After 10th trapping: Plot of Population Estimates Population Size Trapping Period 4

5 Exercise 2: Still Traps Actual Population Size: Estimated Population Size After 1st trapping: After 6th trapping: After 2nd trapping: After 7th trapping: After 3rd trapping: After 8th trapping: After 4th trapping: After 9th trapping: After 5th trapping: After 10th trapping: Plot of Population Estimates Population Size Trapping Period 5