The estimation of population size and the analysis of spatial distribution in a population of immobile organisms

Population ecology is the study of the dynamics of organisms and there interaction within the community. It is important for us to study the interactions of different species within the habitat in order to understand each species niche and in order to ensure sustainability and maintain the habitat. Previous studies have shown how human interaction and the introduction of infrastructure affects habitats such as the study by Turra,A and Denadi,M.R in Brazil, where they noticed that due to intense urbanization, new habitat and new organisms were found to colonize the newly formed rocky areas.

Biodiversity is essential for human survival and economic well being and for the ecosystem function and stability (Singh, 2002). Over exploitation and incorrect habitat management can lead to severe consequences such as the loss of biodiversity. With this citied, it is important to be able to take precautions with careful planning and the introduction of sustainable management. A study into an ecosystem or part of an ecosystem can help us understand how to efficiently maintain and survive as one with the environment without causing destruction. Estimation of population size through the use of quadrats, line quadrats, transect sampling through the use of belt transect as well as random sampling are all ways in which population size and diversity within a set area can be measured.

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Analysis of the data through the use of many mathematical equations will then give a more solid idea of the habitat and thus giving us vital information on the area before it can be altered.Sampling areas and collecting data may theoretically seem simple; however there are many aspects that cause much difficulty. One must consider the sheer size of the areas that need to be surveyed to the size of the organisms that occupy that place; for example if a study were to take place in a rainforest in Brazil, one can only realistically survey a fragment of the area and assumptions that the rest of the rainforest is of the same diversity would be incorrect. Also, some areas may be inaccessible/unsafe, so one must take this into consideration when making estimates. However with correct planning of a study and adequate surveying will portray a relatively realistic idea of the place and the diversity within that area.

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 & MethodMaterials 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.