Topic 5.3 Populations

Question 1

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

Answer 1

• Natality increases population size through reproduction (birth rate)
• Mortality decreases population size through death (individuals eaten/die of old age/become ill)
• Immigration increases population size as result of individuals moving into given area from elsewhere
• Emmigration decreases population size as result of individuals moving out of given area to live elsewhere

Overall:

Population Size = ( N + I ) - ( M + E )

Question 2

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

Answer 2

• x-axis: time
• y-axis: population #
• K: carrying capacity
• exponential growth phase (r)
• transitional phase
• plateau phase

Question 3

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

Answer 3

Exponential growth phase - rapid increase in population. This is a result of:

• Natality rate exceeding mortality rate
• Plentiful resources (food) available for all members of the population
• Lack of competition
• Lack of predation
• Lack of disease

Transitional phase - population growth begins to slow. This is a result of:

• Natality rate falling as mortality rate rises
• Decreasing amount of resources
• Increased competition
• Increased predation
• Introduced diseases

Plateau phase - population reaches carrying capacity so size remains constant. This is a result of:

• Natality rate is equivalent to mortality rate
• Limited resources
• Competition present
• Common predation
• Common diseases
• Accumulation of waste (e.g. excrement, CO₂) limiting growth

Question 4

5.3.4 List three factors that set limits to population increase.

Answer 4

1. Resources and competition
2. Predation
3. Disease
4. Build up of waste