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Populations

Explore how population size is influenced by natality, immigration, mortality, and emigration. Learn about the sigmoid population growth curve and its stages - exponential growth, transitional phase, and plateau phase. Discover the factors setting limits to population increase.

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Populations

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  1. Populations Topic 5.3

  2. 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.

  3. 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

  4. Mount Saint Helens 1980 • How is/was the sizes of populations affected by: • Natality? • Mortality? • Immigration? • Emigration?

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

  6. Population dynamics simulation model

  7. 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

  8. Causes of exponential phase • Plentiful resources • Little or no competition from other inhabitants • Favorable abiotic factors • Little or no predation or disease

  9. Causes of the transitional phase • 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

  10. Causes of the plateau phase • 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

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