5.3: Populations

Question 1

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

Answer 1

Natality: increases population size as offspring are added to the population.

Immigration: increases population size as individuals have moved into the area from somewhere else and so this adds to the population.

Mortality: decreases the population as some individuals get eaten, die of old age or get sick.

Emigration: decreases the population as individuals have moved out of the area to go live somewhere else.

Question 2

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

Answer 2

Exponential phase:

• Rapid increase in population growth.
• Natality rate exceeds mortality rate.
• Abundant resources available. (food, water, shelter)
• Diseases and predators are rare.

Traditional phase:

• Natality rate starts to fall and/or mortality rate starts to rise.
• There is a decrease in the number of resources.
• An increase in the number of predators and diseases.
• Population still increasing but at a slower rate.

Plateau phase:

• No more population growth, population size is constant.
• Natality rate is equal to mortality rate.
• The population has reached the carrying capacity of the environment.
• The limited resources and the common predators and diseases keep the population numbers constant.

Question 3

List 3 factors that set limits to population increase:

Answer 3

1. Shortages of resources (food, shelter)
2. Increase in predators
3. Increase in diseases and parasites.