IB BIO TOPIC 5.3 : POPULATIONS

Question 1

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

Answer 1

• natality: birth rate
• immigration: rate at which individuals move into the population
• mortality: death rate
• emigration: rate at which individuals move out of the population

Question 2

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

Answer 2

• lag phase
• Phase 1 exponential phase
• Phase 2 transitional phase
• Phase 3 plateau phase

Question 3

Explain the reasons for the exponential growth phase

Answer 3

1. exponential phase/log phase

population doubles per unit time producing exponential/geometric growth
no limiting factors: nutrients, oxygen, space in ample supply

Question 4

Explain the reasons for transitional phase

Answer 4

2. transitional phase

population growth continues, but at an ever-decreasing rate
limiting factors slow growth rate: nutrients, oxygen, space in ever-shorter supply

Question 5

. Explain the reasons for plateau phase/stable phase

Answer 5

3. plateau phase/stable phase :

population growth slows to zero: population becomes stable limiting factors inhibit growth: nutrients, oxygen, space in short supply

Question 6

List three factors that set limits to population increase.

Answer 6

density-dependent factors :

• mortality due to disease
• mortality due to predation
• intraspecific competition

density-independent factors :

• mortality due to weather