# Increase in population size

```5.3 POPULATIONS
April 18th/2012
Adapted from: Taylor, S. (2010). Populations (Presentation). Science
Factors affecting population size: how can a
population get bigger or smaller.
Population growth curve: how does it grow?
Factors limiting population growth.
Increase in population size:
• Natality is recruitment to a population through reproduction
• Immigration from external populations e.g. Bird migration
Reduction in population size:
• Mortality which is the death rate from any source e.g. predation
• Emigration, where individuals leave the population for another habitat
5.3.1 Outline how population size is affected by
natality, immigration, mortality and emigration.
a) Exponential Phase of rapid
population growth rate
b) Transition stage: A slowing yet still
high growth rate against time or
generations
c) Plateau stage in which the
population remains stable with
time.
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.
With unlimited resources the population would increase exponentially.
In reality, environmental resistance limits the population growth and
determines the carrying capacity of the habitat:
5.3.4 List three factors that set limits to
population increase.
(a) Outline the trends, over the period of time shown in the graph, in the number of
grey partridges, buzzards and sparrowhawks. (3)
(b) (i) Identify the correlation between the density of grey partridges and birds of prey. [1]
(ii) Suggest a hypothesis to account for this correlation. [2]
(c) (i) Calculate the percentage of deaths due to birds of prey. [1]
(ii) Using the data provided, discuss the causes of the correlation between the density
of grey partridges and the density of birds of prey. (3)
2. Which factors can cause a decrease in a population?
Emigration
Natality
Immigration
A.
Low
High
Low
B.
High
Low
High
C.
High
Low
Low
D.
Low
High
High
(Total 1 mark)
Mortality
High
Low
High
Low
3. Which of the following statements describe a “population”?
A.
All the autotrophs and heterotrophs living in a certain area
B.
Individuals belonging to the same species in a certain area
C.
Two geographically isolated groups belonging to the same species
D.
A group of different species living in the same area at the same time
(Total 1 mark)
4. In the graph below, what could be causing the population change in the region II &reg; III?
A.
Natality &gt; mortality, immigration = emigration
B.
Natality &gt; mortality, immigration &gt; emigration
C.
Natality &gt; mortality, immigration &lt; emigration
D.
Natality = mortality, immigration &lt; emigration
(Total 1 mark
5. Which factors can limit population growth?
I.
Shortage of food
II.
Increased genetic variation in the population
III.
Increase in predators
IV.
Increase in diseases and parasites
A.
B.
C.
D.
I and II only
I and III only
I, III and IV only
I, II, III and IV
```