Exercise 4. Terrestrial Sampling Techniques

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Experiment 4

Terrestrial Sampling Techniques

K. Draheim, B. N. Estrella, K. M. L. Garcia, L. Guillermo

Department of Biological Sciences, College of Science, University of Santo Tomas, España Street, Manila 108 Key words: Point-Quarter Quadrat, Relative abundance Relative density Sampling, Transect Summary

Sampling is the selection of units from a population of interest in order to come up with generalized inferences regarding the population as a whole. In the exercise, quadrat, transect and point-quarter methods were applied to a sample of candies representing Narra and Fan-tail species. Among the three methods, quadrat method was able to give a better impression of the actual composition of the area occupied by candy samples in comparison to transect and point-quarter method. Utilizing Shannon index, Simpson’s index and Jaccard’s index, site 3 was generally the site for high diversity for both Narra and Fan-tail.

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Introduction

Sampling is a vital component of ecology. It is the process of picking out units from a population of interest in order to come up with fairly generalized inferences regarding the population as a whole (Trochim 2006). It solves the problem in determining population distribution, magnitude, and changes in profusion. Samples are always random wherein all possible combinations of the sampling units have an equal chance of being chosen.

There are three commonly used sampling techniques for non-mobile organisms: Quadrat, belt/line transect, and point-quarter.

In the quadrat method, a series of squares (also termed “quadrats”) of a set size are situated in the study habitat and the species that fall within those squares are identified and catalogued. Ecologists carefully sort through each quadrat to count and identify the subject organisms. Taking photos of each quadrat is also useful for future analysis of the area. Quadrat sampling methods are best suited for coastal areas which are relatively accessible. The Natural Geography inshore Areas (NaGISA) project has been utilizing this method as their main sampling technique in their research (CML, 2009).

Systematic sampling involves selecting samples at fixed intervals, commonly along a line. This usually requires doing transects wherein a sampling line is positioned across regions of environmental gradients. An environmental gradient is a progressive change in abiotic factors through space or time. Two kinds of systematic sampling are the line and belt transect methods. Line transects are used to show environmental gradients or linear patterns along plant communities. This allows researchers to clearly visualize the changes happening along the line. However, line transects do not give much information regarding relative densities of particular species. Belt transects are basically similar to line transects. The two differ in a way that belt transects give information on the abundance and presence or absence of the species (OWWT, 2000).

The point quarter is a plotless method used to approximate density. This technique assumes that the subject species follow a random spatial pattern. To apply this method, a set of points along a transect is selected. The area surrounding each point is divided into four

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quadrants. The organism closest to the point in each quadrant is noted. The distance between the central point and the selected organism in each quadrant is determined. The distances for all the sample points are averaged. The point quarter method is usually used in wide varieties of vegetation types (ABR, 2016).

Objectives

1. To be able to learn some of the methods in taking representative samples from the real world

2. To be able to gain an accurate assessment of the composition of a measured area by looking at a few samples from that area

3. To be able to compare three field sampling techniques to sample candies in an area Methodology

The following materials were used in the experiment: tally worksheets (Appendix IV), pencils, erasers, improvised transect lines, 1.0x1.0 m2 _{quadrat, and a scientific calculator.}

Each group was assigned an establishing sample area along the floor of Lab-13. Each group employed all three methods to sample the candies. For group 3, Narra and fan-tail counterparts of the candies were counted.

Quadrat Method: A random number was used to select a point somewhere on the baseline. Another random number was chosen, this one less than 55, to represent a distance in meters from the baseline. On a line perpendicular to the baseline, a point was establish randomly as distance from the baseline. That point was used as the lower left corner of the quadrant. The relative abundance of each candy sample was calculated.

Transect Method: A random number was used (between 0 and 60) and a spot was determined on the baseline. An approximate 20m line was established perpendicuar to the baseline through the point. This transect was used to identify and score every candy on the line. The relative density (RDi) of each candy was also calculated.

Point-Quarter Method: A random number was selected on a point in the baseline. Another number was selected and moved at a distance in meters on a line perpendicular to the baseline. The point ate end of the line served as the origin of a set of Cartesian coordinates with the Y-axis coinciding with a north-south axis and the X-axis coinciding with an east-west axis. Four quadrants were thus established.

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The following formulas were used to obtain the succeeding data H' =−

∑

i=1 s _n i N ln n_i N D=1−

∑

i=1 s n_i(n_i−1) N (N −1) ni = number of individuals

N = total number of individuals of all species Sj = a .

a + b + c where:

Sj = Jaccard’s similarity coefficient

a = number of species in sample A and sample B (joint occurrences) b = number of species in sample B but not in sample A

c = number of species in sample A but not in sample B FAN-TAIL

Table 1. Tally and result of Quadrat Method, H' (Shannon-Wiener), and D (Simpson) for Fan-tail Quadrat Sit es No. of Specie s H' D 1 3 -0.338385477 0.03846153 8 2 0 0 0 3 4 -0.362663076 0.07692307 7

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4 1 -0.197303797 0 5 2 -0.287969566 0.01282051 3 6 3 -0.338385477 0.03846153 8 7 0 0 0 N 13 1.524707393 0.83333333 3

Table 2. Tally and result of Transect Method, H' (Shannon-Wiener), and D (Simpson) for Fan-tail Transect Sit es No. of Specie s H' D 1 0 - 0 2 0 - 0 3 1 -0.34657359 0 4 1 -0.34657359 0 5 2 -0.34657359 0.166666667 6 0 - 0 7 0 - 0 N 4 1.039720771 0.833333333

Table 3. Tally and result of Point-Quarter, H' (Shannon-Wiener), and D (Simpson) for Fan-tail Point-Quarter Site s No. of Speci es H' D 1 0 -

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-2 0 - -3 0 - -4 0 - -5 0 - -6 0 - -7 0 - -N 0 0 -NARRA

Table 4. Tally and result of Quadrat Method, H' (Shannon-Wiener), and D (Simpson) for Narra Quadrat Sit es No. of Specie s H’ D 1 0 - 0 2 1 -0.188504095 0 3 4 -0.357932277 0.065934066 4 3 -0.330095366 0.032967033 5 1 -0.188504095 0 6 3 -0.330095366 0.032967033 7 2 -0.277987164 0.010989011 N 14 1.673118363 0.857142857

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Transect Site s No. of Speci es H’ D 1 0 - 0 2 0 - 0 3 0 - 0 4 1 -0.34657359 0 5 0 - 0 6 0 - 0 7 1 -0.34657359 0 N 2 0.693147181 1

Table 6. Tally and result of Point-Quarter Method, H' (Shannon-Wiener), and D (Simpson) for Narra Point-Quarter Site s No. of Speci es H’ D 1 0 - -2 0 - -3 0 - -4 0 - -5 0 - -6 1 0 -7 0 - -N 1 0

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-Table 7. Result of Jaccard’s similarity coefficient Sampling sites

compared

Sampling technique

Quadrat Transect Point-quarter

Sj Similarit y Sj Similarit y Sj Similarit y

1,2 0 low 0 low 0 low

1,3 0.5 high 0 low 0 low

1,7 0 low 0 low 0 low

2,7 1 high 0 low 0 low

3,4 1 high 1 high 0 low

3,5 1 high 1 high 0 low

4,5 1 high 0.5 high 0 low

4,7 0.5 high 0.5 high 0 low

Discussion

Line transect sampling is a popular method used to estimate population density. The probability density of perpendicular sighting distances from randomly placed transect lines are modeled to derive an estimate of population density. For all transects performed, Narra is the more dominant species between the two, constituting most of the total population of species and the other species Fan-tail constitutes the remaining population.

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Quadrats, on the other hand, are used to define sample areas within the study area. The quadrat method allows the user to define a fixed area, called a plot; within which species characters can be measured. Usually, a rectangular quadrat frame is used to define the sampling area, although a quadrat can also be a permanently established area within a site. Although the exact experimental design will determine where and how many samples are taken, the procedure always involves measuring species characters of only those that are inside the quadrat.

For this exercise, four quadrats were surveyed and the following results were obtained: Narra is dominant in quadrats 1 and 4. On the other hand, Fan-tail is dominant in quadrats 3. While in quadrat 2 both Narra and Fan-tail have almost the same number of species.

The point-quarter method relies upon a random distribution of the organisms in the area to be sampled. Uniform or clumped distributions will yield erroneous results. However, this method is one of the most favored for sampling.

In addition to the three sampling techniques utilized in the actual experimentation, other measures (indices) to quantify the species diversity of the area of study were applied. The Shannon index (H , also termed the Shannon-Wiener index) and the Simpson index (D) wereʼ used to interpret both species richness (number of species present) and relative abundance (dominance or evenness). The Shannon index increases as both the richness and the evenness of the community increase. For Fan-tail, site 3 (quadrat method) obtained a value of -0.36266, indicating high diversity of Fan-tail in comparison to the other six replicates; as for transect method, site 3, 4 and 5 represent high diversity with same values of -0.3579, in site 6 Fan-tail is less diverse, sites 1 and 2 did not produce any values for Shannon-Wiener index; point-quarter did not reproduce any values for Shannon-Wiener index. For Narra, site 3 (quadrat) again indicated high diversity of Narra among replicates with a value of -0.3579. Site 4 and site 7 obtained a value of -0.35793 for Transect, which are sites with high diversity. Site 1,2,3, and 6 (Tansect method) and all sites for Point-quarter method did not produce any values for Shannon-Wiener index.

Simpson s index (D) is based on the probability of any two individuals drawn at randomʼ from an infinitely large community belonging to the same species. D is a measure of dominance, so as D increases, diversity (in the sense of evenness) decreases. In the seven replicates, Fan-tail

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was the more dominant species in site 3 (Quadrat method) and site 5 (Transect method), whereas Narra was the more dominant species in site 3 (Quadrant method), in comparison to the other sites.

To compare diversity among communities, Jaccard s similarity index was used. Thisʼ index will quantify not just the diversity of a single site, but in comparing biodiversity levels across sites. Jaccard s index only utilizes the richness component of diversity, since it does notʼ entail any information on abundance. For quadrat method, only site 1 and 7 are low in similarity. For Transect method, 3 and 4, 3 and 5, 4 and 5, and 4 and 7 were the only compared sites with a high similarity. For point-quarter method all compared sites obtained low similarity.

Conclusion

In the exercise conducted, quadrat method, transect method and point-quarter method were effective tools in assessing population distribution of the representative species taken into account. Among the three field sampling techniques, point-quarter method determined the least sample candies in the area, observing only one Narra and no fan-tail among the seven replicates. Unlike Quadrat and Transect method, samples were relatively distributed in the different areas of the different replicates. Quadrat method was able to record the most number of samples for both Narra and fan-tail species. The Shannon index (H , also termed the Shannon-Wiener index) andʼ the Simpson index (D) were used to quantify biodiversity while Jaccard s similarity index toʼ compare diversity between sites. Site 3 was generally the site for high diversity for both Narra and Fan-tail.

REFERENCES

Trochim, W. (2006). Sampling. Retrieved March 6, 2016 from http://www.socialresearchmethods.net/kb/sampling.php

Census of Marine Life. (2009). Quadrat sampling. Retrieved March 6, 2016 from http://www.coml.org/investigating/observing/quadrat_sampling

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from http://www.countrysideinfo.co.uk/3howto.htm

Arizona Board of Regents. (2016). Point-centered quarter methods. Retrieved March 6, 2016 from http://globalrangelands.org/inventorymonitoring/pointcentered