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Populations. Topic 5.3. Assessment Statements. 5.3.1 Outline how population size is affected by natality, immigration, mortality and emigration. 5.3.2 Draw and label a graph showing a sigmoid (S-shaped) population growth curve.

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Populations l.jpg

Populations

Topic 5.3


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Assessment Statements

  • 5.3.1 Outline how population size is affected by natality, immigration, mortality and emigration.

  • 5.3.2 Draw and label a graph showing a sigmoid (S-shaped) population growth curve.

  • 5.3.3 Explain the reasons for the exponential growth phase, the plateau phase and the transitional phase between these two phases.

  • 5.3.4 List three factors that set limits to population increase.


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Outline how population size is affected by natality, immigration, mortality and emigration.

  • Natality – # of new members of the species due to reproduction

  • Mortality - # of deaths

  • Immigration – members arriving from different places

  • Emigration – members leaving the population


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Mount Saint Helens 1980 immigration, mortality and emigration.

  • How is/was the sizes of populations affected by:

    • Natality?

    • Mortality?

    • Immigration?

    • Emigration?




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Sigmoid (S-shaped) curve of the graph shows three stages in population growth

  • Exponential growth phase – a.k.a. logarithmic phase, in which the # of individuals increases at a faster and faster rate

  • Transitional phase – growth rate slows down considerably

  • Plateau phase – stationary phase, in which the # of individuals has stabilized


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Causes of exponential phase population growth

  • Plentiful resources

  • Little or no competition from other inhabitants

  • Favorable abiotic factors

  • Little or no predation or disease


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Causes of the transitional phase population growth

  • Increasing competition for resources among individuals of population

  • Predators, attracted by a growing food supply, move into the area

  • b/c of large numbers of individuals living together in a limited space, opportunities for disease to spread within the population increase


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Causes of the plateau phase population growth

  • Less and less space

  • Limited supply of food, animals tend to have smaller numbers of offspring

  • Predators and disease increase mortality and the growth curve tends to level off

  • # of births plus the # of immigrants is balanced with the # of deaths plus the # of emigrants


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List three factors that set limits to population increase. population growth

  • The maximum number of individuals that a particular habitat can support is called the carrying capacity and it is represented by the letter K.

  • Limiting factors:

    • Availability of resources

    • Build-up of waste

    • Predation

    • Disease


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