3 Environmental systems and societies PSL, Assignment II, Max. Marks: 20Students investigated a community of trees by sampling a total area of 20 000 m2.SpeciesNumber of plantsDouglas fir (Pseudostuga menziesii)30Big Leaf Maple (Acer macrophyllum)60Grand Fir (Abies grandis)240(a)Calculate the plant density for the Grand Fir.240/20000 = 0.012 (1) (b)Describe the method used to collect this data.The method used is estimating density. Estimating density is the mean of the number of organisms present per square area. The process to calculate this is by calculating the number of the required organisms in every quadrant and then find the mean of all the calculated quadrants. (3) (c)Explain why populations show a sigmoidal growth curve.In a population, the organisms grow quickly. This marks the upward curve of the sigmoidal curve. Then the organisms mature and the curve flattens out a bit. The next process is the declination stage where the organisms become old and weak. These become easy prey to other predators. Thus this becomes the downward curve in the sigmoidal curve. As a result population displays an S-shaped curve. (3) (Total 7 marks)2.(a)Define the term species.Species are a group of organisms are a group of similar individuals that are capable of interbreeding with each other. They are the basic taxonomic unit. (1) The figure below shows the vegetation change over time.(b)(i)State the name of the process shown in the diagram above.Succession. (1) (ii)Outline what is meant by the term climax vegetation and identify which part of the diagram above (A, B or C) contains climax vegetation.Climax vegetation is the type of vegetation that can establish itself on any given environmental condition and in the absence of any major disturbances.C shows the climax vegetation. (2)(iii)Suggest two ways in which human activity could affect climax vegetation.Deforestation.Pollutants emitted by factories. (2) (c)(i)Draw S and J population growth curves on the axes below. Label each graph and the axes.PopulationTimePopulationTime (2)(ii)Identify in which part of the diagram above (A, B or C) you would expect to find species withS population growth curves. C and BJ population growth curves. A and B(2) (d)Explain why ecosystems in later stages of succession are likely to be more stable.This is because the ecosystem has reached its maximum carrying capacity. The carrying capacity of an environment is the maximum number of organisms it can sustainably hold. (2) (e) Explain why the amount of organic matter increases as succession occurs.Succession is a naturally recurring process in the ecosystem. Succession is the process of change in the species structure of an ecological community over time. Thus the amount of organic matter keeps increasing as the rate of reproduction is quite high and the death rate less. As a result there are more organisms and as they die, the amount of organic matter increases. (1)