Population size and competitionAQA A-Level Biology: Subtopic test

1. 1
   A conservation team monitors a population of red deer on an island with no natural predators. Over 40 years the population rose, then levelled off and now fluctuates around 1200 animals. The island's vegetation provides a limited food supply and little shelter in winter.

   (a)

   What term describes the population size of about 1200 around which the deer population fluctuates?

   [1 mark]

   • ABiodiversity
   • BCarrying capacity
   • CNiche
   • DSuccession

   (b)

   Which of the following is an abiotic factor that could reduce the deer population?

   [1 mark]

   • AAn increase in parasites
   • BCompetition between deer for grazing
   • CAn outbreak of disease
   • DA severe winter with very low temperatures

   (c)

   Explain why the deer population does not continue to increase above about 1200.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Two species of barnacle, X and Y, live on a rocky shore. Both attach to rock and feed by filtering plankton from the water. Species Y grows faster and smothers species X in the lower zone of the shore, but Y cannot survive long exposure to air in the upper zone.

   (a)

   Which term describes the competition between species X and species Y?

   [1 mark]

   • AInterspecific competition
   • BIntraspecific competition
   • CPredation
   • DSuccession

   (b)

   Which of the following is an example of intraspecific competition?

   [1 mark]

   • ASpecies X being smothered by species Y
   • BSpecies Y being killed by drying out in the upper zone
   • CIndividual Y barnacles competing for attachment space on the rock
   • DSpecies X and Y both feeding on plankton

   (c)

   Suggest why species X is found only in the upper zone when species Y is present.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Records of a population of snowshoe hares and of the lynx that feed on them were collected over many decades in a boreal forest. Both populations rise and fall in regular cycles with peaks about 10 years apart. Each lynx peak occurs one to two years after the hare peak. Hares feed on vegetation, and lynx feed mainly on hares.

   (a)

   Explain why each peak in the lynx population occurs after the peak in the hare population.

   [3 marks]

   (b)

   Explain how predation leads to the fall in hare numbers and then to the fall in lynx numbers, and suggest one other factor that could cause hare numbers to fall.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   The native red squirrel has declined in much of Britain since grey squirrels were introduced from North America. Both species live in the same woodland and feed on seeds such as acorns and hazelnuts. Grey squirrels are larger and reach much higher population densities. Many grey squirrels carry a virus that rarely harms them but is often fatal to red squirrels.

   (a)

   Explain why the red squirrel population has declined in woodland where grey squirrels have been introduced.

   [6 marks]

   (b)

   In woods where the virus was absent, red squirrels disappeared about 15 years after greys arrived. In woods where the virus was present, they disappeared in about 5 years. In conifer woods, where greys digest seeds less efficiently, red squirrels persisted for much longer. Evaluate the claim that interspecific competition, rather than the virus, is the main cause of the decline of red squirrels.

   [6 marks]

   Total for question 4: 12 marks

End of questions