5.3 POPULATIONSApril 18th/2012

Adapted from: Taylor, S. (2010). Populations (Presentation). Science Video Resources. [Online] Wordpress. Retrieved from

http://i-biology.net/ibdpbio/populations/

Factors affecting population size: how can a population get bigger or smaller.

Population growth curve: how does it grow?

Factors limiting population growth.

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

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

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

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.

5.3.3 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.

With unlimited resources the population would increase exponentially.In reality, environmental resistance limits the population growth and

determines the carrying capacity of the habitat:

(a) Outline the trends, over the period of time shown in the graph, in the number ofgrey 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 densityof grey partridges and the density of birds of prey. (3)

2. Which factors can cause a decrease in a population?Emigration Natality Immigration Mortality

A. Low High Low HighB. High Low High LowC. High Low Low HighD. Low High High Low(Total 1 mark)

3. Which of the following statements describe a “population”?A. All the autotrophs and heterotrophs living in a certain areaB. Individuals belonging to the same species in a certain areaC. Two geographically isolated groups belonging to the same speciesD. 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 ® III?

A. Natality > mortality, immigration = emigrationB. Natality > mortality, immigration > emigrationC. Natality > mortality, immigration < emigrationD. Natality = mortality, immigration < emigration(Total 1 mark

5. Which factors can limit population growth?I. Shortage of foodII. Increased genetic variation in the populationIII. Increase in predatorsIV. Increase in diseases and parasites

A. I and II onlyB. I and III onlyC. I, III and IV onlyD. I, II, III and IV