D4.2 Stability and change
Stability and change in ecosystems depend on sustainable resource use, pollution impacts, keystone species, rewilding, and succession processes over time.
- Syllabus
- First assessment 2025
- Topic
- D4.2
- Level
- SL
Exam analysis
Chance of appearing24%of analysed past papers
Latest appearanceMay 2025
Most common paperPaper3
Typical marks1–3
Most tested objectives
Common question formats
- Comparison
- Data analysis
- Definition or recall
- Evaluation
- Extended response
- Process explanation
- Structured response
Recent exam appearances
May 2025Paper2 ["SL"] · TZ24(c)[ 2 ]D4.2.11—Rewilding
May 2025Paper2 ["SL"] · TZ24(b)[ 2 ]D4.2.5—Keystone species
May 2025Paper2 ["SL"] · TZ24(a)[ 2 ]D4.2.5—Keystone species
May 2025Paper1A ["SL"] · TZ130[ 1 ]D4.2.8—Eutrophication
May 2025Paper1A ["SL"] · TZ329[ 1 ]D4.2.11—Rewilding
Practice this topic
Coverage 2010–2025 · Updated 16 Jul 2026
Objective notes
11 learning objectives• Some ecosystems remain stable over long timescales despite local fluctuations
• Ancient forests, deserts, and long-lived communities provide evidence of stability
• Stability requires energy input, nutrient cycling, biodiversity, and genetic diversity
• Abiotic conditions must remain within tolerance ranges for key species
• Amazon deforestation reduces transpiration, rainfall recycling, and regional cooling
• Loss of forest can push rainforest toward savanna-like tipping points
• Mesocosms model ecosystem stability under controlled experimental conditions
• Closed bottle systems restrict matter exchange but allow light energy input
• Keystone species have disproportionate effects on community structure
• Removal can trigger trophic cascades and ecosystem instability
• Sustainable harvesting removes biomass at or below replacement rate
• Managed plant harvests and marine fish stocks require monitoring population recovery
• Agricultural sustainability depends on soil conservation, nutrient balance, and biodiversity
• Erosion, leaching, fertilizers, agrochemicals, irrigation, and carbon footprint are key factors
• Eutrophication follows nitrate and phosphate enrichment of water
• Algal blooms, decomposition, high biochemical oxygen demand, and hypoxia harm aquatic life
• Biomagnification increases toxin concentration at higher trophic levels
• DDT and mercury show how top predators receive the highest doses
• Macroplastics and microplastics persist, fragment, and move through marine ecosystems
• Effects include entanglement, ingestion, toxin transport, and food-web impacts
• Rewilding restores natural processes, trophic interactions, and habitat connectivity
• Keystone species reintroductions can restart trophic cascades and reduce intensive management