This report is a follow-up of a practical which was done in two parts and was focused on the use of quadrats to estimate population size and quantify spatial distribution by looking at the results and using mathematical equations to make conclusions.
Materials & Method
Materials provided:
Two maps of the locations of organisms, distribution A and distribution B.
Transparent overlay indicating position of 12 quadrats.
Placing the transparent overlay on top of distribution A (ensuring the edges are aligned perfectly), showed the number of organisms in quadrat 1 and the results were noted in the table (Table 1). At this point no mean was calculated as there was only one sample. After that, the number of organisms in quadrat 2 was citied and again noted in the table and then the mean was calculated. This was done for all the quadrats on the overlay until the table was complete, following this; equation 1 was used to fill the last column of the table “Population estimate”.
By using the last row of the results on table 1, another table was now drawn (table 2) to calculate the variance of the results and using equation 2, the variance was calculated for distribution A. Following this another table was drawn table 3 to calculate the index of dispersion, using equation 3 and the results from the previous tables, table 3 was complete for distribution A. The images (appendix 1) were used to determine whether the population was deemed uniform, random or clumped. The whole procedure was repeated for distribution B however tables were not needed as population estimate was not needed to be calculated.
Results
Table 1
This table was drawn in order to input the results for the experiment at hand. The results are from the materials and methods section. The table shows the mean number of organisms in the area (shown in the mean column) and the population estimate. The population estimate was used to plot Graph 1. 12 quadrats were sampled, each quadrat was 1metre squared in size and the number of organisms per quadrat is shown in red.
Equation 1
Population estimate= Mean number of organisms per quadrat X Total area being samples/ Area of quadrat
This equation was used to fill in the last column which is the population estimate, this was used in order to plot Graph 1.
Table 2
This table was drawn in order to work out the variance, which in turn would allow working out the index of dispersion. The numbers in the column “X” are taken from the original data in table 1 from the last column, the mean was also worked out from the data. Equation 2 was used to work out the variance using the table above.
Equation 2
Variance =
N= Represents the number of samples, which in this case was 12.
Table 3
This table shows how the description of the two populations was deduced. The mean and variance were used to calculate the index of dispersion, which is Mean/Variance. Once the index was found, one can deduce how the population is spread out.
In random distribution, Variance equals the mean so I=1
Uniform distributions have a value of I<1
Clumped distributions have a value of I>1.
Graph 1
This graph shows the relationship between the number of quadrats (x-axis) samples and the population estimate (y-axis) obtained. The horizontal bold line shows the actual number of organisms in that area. As you can see from the graph, the population estimate is higher than the actual population in the area.
Discussion
After analysis of the results, it is evident that distribution A has a clumped degree of dispersion and distribution B has a uniform degree of dispersion. The dispersion of species was studied based on the variance to mean ratio (Greig Smith, 1983). A ratio of 1:1 would indicate a random distribution, if the index of dispersion was greater than 1 then it would be a clumped dispersion, and index of dispersion of less than 1 would indicate a uniform dispersion; Therefore it can be concluded from the results in table 3, which show that distribution A has an index of dispersion of 0.9 and distribution B has an index of dispersion of 1.96.
Distribution A showed a relative consistency of mean number of organisms per quadrat ranging from a low of 4.1 to a high of 5.6, This ties in with the theory that it is a clumped distribution as it shows a higher number of organisms per quadrat then that shown of distribution B. Distribution B showed a mean number of organisms per quadrat as 3.16, which supports the basis that it is a uniform dispersion.
As there was only 12 quadrats used for both of the distributions, it is adequate to come to a conclusion based on the theory; However the use of more quadrats would increase the accuracy of the results as there would be a larger surface area covered. The two areas of distribution were simulation models, which do not give accurate in comparison to a real life study which you would be able to see the different species in the area. The way in which the quadrats were placed in the simulation meant that there were gaps in between the quadrats which could have sustained the same organisms and thus changed the results. In a real life study, there are many ways in which one can alter the quadrats used depending on the vegetation of the land for example the use of a 1 metre quadrat to measure algae and lichens dispersion would be inaccurate, as it would be to do the same for trees with the small quadrat. The use of different size quadrats in a real life field study would give more consistent accurate results, as it would take into account the area which is being observed to the equipment being used.
Clumped distribution is one which is most found in natural areas, and is mostly found in areas which show patchy resources. Distribution A is of clumped dispersion and in a real life field study such as in African wildlife a group of dogs known as lycoan pictus, which tend to remain in dense formations next to each other in order to ensure survival and due to hunting methods, as they hunt in groups (Creel, N.M. and S. ,1995).
Uniform distribution which is shown through the results of distribution A, are less common in real life studies. These tend to show large distances between neighbouring individuals, this tends to happen due to competition for nutrients and space between species and therefore causes a large spread. Plants tend to exhibit uniform distribution such as salvia leucophylla which grows naturally in uniform distribution in California (Mauseth James,2008).
Graph 1 shows the population estimate against the number of quadrats used. The bold line shows the actual number of organisms in the area which is 150; however the population estimate showed a range from 172 to 240 which is much larger than the actual number of organisms in that area. This is could be because the number of quadrats used for that area is too little or the quadrats used were not of relative size to the organisms in that area. Increased precision would show more correlation between the actual population and the population estimate.
References
Turra,A and Denadi,M.R 2006- Article
Singh,2002- Article
Greig smith, 1983- Scientific journal
Creel, N.M. and S. (1995). "Communal Hunting and Pack Size in African Wild Dogs, Lycaon pictus". Animal Behaviour: 1325–1339
Mauseth, James (2008). Botany: An Introduction to Plant Biology. Johns and Bartlett Publishers. pp. 596. ISBN 0763753459.
R. Sagar, A.S. Raghubanshi*, J.S. Singh Department of Botany, Banaras Hindu University, Varanasi 221005, India
Life, The science of biology, Sinauer associates, ISBN: 9781429254311