Populations and energy flow structure whole ecosystems. This HL lesson covers C4.1 Populations & communities and C4.2 Transfers of energy & matter.
You will model growth and succession, distinguish gross and net production, and use mark-recapture and efficiency calculations.
Work through each screen, answer the questions as you go (some are wordy, some are calculations) and collect ⭐ stars. Press Start when you are ready.
C4.1 Populations
Populations, communities and succession
Populations grow in a sigmoid curve limited by density-dependent factors (competition, disease, predation) and density-independent factors (weather, disasters).
Succession changes communities over time: primary starts on bare rock with pioneer species (e.g. lichens); secondary starts on existing soil. Keystone species have effects far larger than their abundance.
Calculate
Your turn — calculate
1In a mark-recapture study, 60 animals were marked (M). A later sample of 40 (n) contained 12 marked (m). Estimate the population size N = (M × n) ÷ m.
animals
Hint: N = (60 × 40) ÷ 12 = 2400 ÷ 12.
C4.2 Energy transfer
Gross and net production (HL)
Gross primary production (GPP) is the total energy fixed by producers. Some is used in the producers' own respiration (R); the rest is net primary production (NPP), available to consumers.
NPP = GPP − Rsecondary production is the energy stored by consumers
Only about 10% of energy passes between trophic levels, so pyramids of energy narrow upward.
Calculate
Your turn — calculate
2Gross primary production is 9000 kJ/m²/yr and producer respiration is 3500 kJ/m²/yr. Calculate the net primary production.
kJ
Hint: NPP = GPP − R = 9000 − 3500.
Calculate
Your turn — calculate
3Producers contain 20000 kJ; the primary consumers feeding on them contain 1800 kJ. Calculate the energy transfer efficiency as a percentage.
%
Hint: efficiency = (1800 ÷ 20000) × 100.
Sort it
Sort each item into its group
Sort each item by category.
Density-dependent factor
Density-independent factor
Producer production term
Quick check
Question
?During primary succession, the first organisms to colonise bare rock are...
Quick check
Question
?Net primary production is the energy available to...
Quick check
Question
?Removing a keystone species from a community usually causes...
Match it
Match each item to its partner
Match each ecological term to its description.
Item
Partner
Quick check
Question
?A density-dependent factor that limits a population is...
Recap
The big ideas to take away
C4.1: sigmoid growth; density-dependent vs independent factors; succession; keystone species
C4.2 (HL): GPP, R and NPP (NPP = GPP − R); ~10% transfer efficiency
Skills: mark-recapture N = Mn/m; NPP and efficiency calculations
Interdependence: producers, consumers and decomposers link energy and matter
Press Finish to see your score.
🏆
Mini-lesson complete!
⭐⭐⭐
You have worked through Theme C: Interaction — Populations & Ecosystems for IB Diploma Biology. 🎉
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