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IB Biology HL C4.1.16 Predator Prey Relationships Questions

Analyse predator-foraging data, time-lagged feedback, predator removal and resistance outcomes to judge predator–prey population dynamics in IB Biology HL C4.1.16.

Syllabus
First assessment 2025
Course
Biology HL
Level
HL

Exam points

  • Interpret predator-foraging or predator–prey data to test whether predator behaviour depends on prey density or predator number.
  • Explain density-dependent predator–prey feedback and time lags linking prey abundance, predator abundance and population cycles.
  • Evaluate predation evidence, including predator removal or disease-resistance outcomes, to judge changes in distribution and population persistence.

IB Biology HL C4.1.16 Predator Prey Relationships Questions question 1

[Maximum number: 3]

The shore crab (Carcinus maenas) forages for food in the intertidal zone on rocky seashores. An experiment was carried out to assess predation at specified levels of food abundance. An area of shore was enclosed in a wire cage. All other food was removed from the encaged area except the mussels provided by the investigators. The number of mussels consumed was measured while the crabs foraged at densities of one, two or four crabs per cage.

Figure for Question IB Biology HL C4.1.16 Predator Prey Relationships Questions question 1 — IB Biology HL

Question (a)

(a)

Suggest a reason for the plateau in the graph when only one crab is present in the cage.

[ 1 ]

Question (b)

(b)

Determine whether foraging by crabs is dependent on number of prey (mussels) or number of predators (crabs).

[ 2 ]
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