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IB ESS HL 2.5.11 Hl R and K Strategist Species Questions

Classify r- and K-strategists from life-history evidence and explain why r-strategists colonise pioneer communities effectively.

Syllabus
First assessment 2026
Course
ESS HL
Level
HL

Exam points

  • classify a named species as an r- or K-strategist from offspring number, maturity, lifespan, parental care, growth rate or survivorship evidence
  • explain why r-strategists are suited to pioneer communities by linking rapid reproduction, dispersal, colonisation and tolerance of harsh or unstable conditions

IB ESS HL 2.5.11 Hl R and K Strategist Species Questions question 1

[Maximum number: 1]
Figure 9(b): Round goby (Neogobius melanostomus)

Figure A:Round goby (Neogobius melanostomus)

Figure 9(b): Mottled sculpin (Cottus bairdii)

Figure B:Mottled sculpin (Cottus bairdii)

Figure:Fact file on the round goby (Neogobius melanostomus)

• An invasive species from Asia.
• First discovered in the St Lawrence River in 1990.
• Females lay eggs three times a year; up to 5000 eggs at a time.
• Young fish mature quickly.
• Can eat up to 4000 eggs of other fish in 15 minutes.
• Aggressively defend the best egg-laying sites, out-competing the native mottled sculpin (Cottus bairdii).
• Eat invasive zebra mussels.
• Eaten by native fish, such as lake trout and yellow perch.

Using Figures 9(a) and 9(b), identify one feature of the round goby that shows it is an r-selected species.

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