The relationship between species, populations community and the ecosystem Developed by KZN advisors

Carrying capacity is the maximum population size a certain environment can support for an extended period of time, for a population of a particular species. Under ideal conditions, a population naturally increases until it overshoots the carrying capacity. At this point, the environment can no longer provide for the species, due to a number of different environmental resistances, including food, crowding, competition, etc. The population, due to lack of resources, will begin to die out, allowing the environment to recover. As the environment recovers, the species population is able to flourish once more. This leads to a fluctuation between the prosperity of the species and the prosperity of the environment (hence the fluctuations in the graph). Developed by KZN advisors

Carrying capacity Developed by KZN advisors

If a population reaches carrying capacity it can remain stable or move up and down (fluctuate). If there is more rainfall and more food available the carrying capacity increases and the population will increase until it reaches the new carrying capacity before it levels off again. If there is habitat destruction or a draught the carrying capacity decreases and the population will decrease until it reaches the new carrying capacity and levels off again. Developed by KZN advisors

Carrying capacity of rabbits in a specific area 1. What does the blue line represent? What does the purple line represent? What does it mean when the purple line rises above the blue line? 2. Which of the following situations might cause the purple line to decrease below the blue line: abundant food sources, lack of competition, a young population, or plentiful roaming space? 3. Can you think of any events that would cause the purple line to stay above the blue line indefinitely? Developed by KZN advisors

1.1 Suggest THREE reasons why the growth form between the period 1920 and 1935 is as it is. 1.2 What is the growth phase called between 1910 and 1920?(1) 1.3 During which year did the jackal enter the fenced area? Give a reason for your answer from the information supplied.(3) 1.4 Between 1940 and 1950 the springbok population increased again. Mention a possible reason for this increase.(2) 1.5 Mention FOUR other factors, besides the jackals, which could have caused the decline in the springbok population between 1935 and 1940?(4) 1.6 What method was most probably used to determine the size of the springbok population? (1) 1.7 Do you think the line representing the carrying capacity is accurate? Give a reason for your answer.(3) 1.8 The population between 1965 and 1975 appears to have stabilised. Suggest how the farmer might be controlling the population.(2) 1.9 What do you notice about the growth from 1915 – 1925 and 1940 – 1950?(1) (20) Question: Carrying capacity Developed by KZN advisors

Density dependent and factors Density dependentDensity independent a density-dependent factor affects a greater percentage of individuals in a population as the number of individuals increases; it will also affect each individual more strongly. Population growth declines because death rate increases, birth rate decreases or both. Resource limitation is one such density dependent factor. A reduction in available food often limits reproductive output as each individual produces fewer eggs or seeds. Health and survivorship also decrease as crowding results in smaller, less robust individuals. Many predators concentrate on a particular prey when its population density is high, taking a greater percentage than usual. Density-independent factors affect the same percentage of individuals regardless of population size. Weather, climate and natural disasters such as freezes, seasonal changes, hurricanes and fires are examples; the severity and time of occurrence being the determining factor on what number of organisms is affected. In some natural populations, these effects routinely control population size before density- dependent factors become important Developed by KZN advisors

Geometric growth form (J- curve) Developed by KZN advisors

Logistic growth form (S-shaped curve) Developed by KZN advisors

Question : growth patterns 4. A certain fast growing unicellular micro-organism is cultivated in a sugar solution in a closed test tube at 25 0 C. At regular intervals, samples were taken in order to calculate the population size. The graph below was drawn from the data obtained. Study the graph and answer the questions that follow. 4.1 Which specific organism was most probably cultivated in the test tube? (1) 4.2 Name the growth phases indicated by A, B and C respectively. (3) 4.3 Give an explanation for the specific growth pattern of each of the phases A, B and C. (6) 4.4 What is phase Y called and what is the possible cause, thereof, for this specific population in particular? (3) [ 13 ] Developed by KZN advisors

Comparison between geometric (J-curve) and Logistic (S-curve) Developed by KZN advisors