4.10.1Additional lessons
Stability in Ecosystems — IB Biology SL Revision Notes & Topical Questions
5 min read 4 parts Lesson 135 of 142
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Part 1 of 4Features of Stable Ecosystems
Stability means an ecosystem's structure and function stay roughly constant over time despite small disturbances. Tropical rainforests have remained stable for millions of years.
Energy supply
- Energy supply A reliable input of energy, usually sunlight, is captured by producers and passed along food chains.
Nutrient recycling
- Nutrient recycling Decomposers return minerals and carbon dioxide to producers, so the ecosystem can support itself.
Genetic diversity
- Genetic diversity A wide range of alleles allows natural selection to favour variants that cope with environmental change.
Tolerable climate
- Tolerable climate Temperature, rainfall and other climatic variables must stay within the limits that the species can tolerate.
High biodiversity
- High biodiversity Many species mean that if one declines, others can continue its role in the food web.
Photosynthesis
- Photosynthesis High light and moisture give fast photosynthesis, as in the Amazon and Congo rainforests, supporting large food webs.
| Requirement | Effect if it fails |
|---|---|
| Energy supply | Producers cannot make food |
| Nutrient recycling | Soil fertility declines |
| Genetic diversity | Population cannot adapt |
| Climate within limits | Species migrate or die |
Part 2 of 4Why Each Feature Matters
The requirements are linkedenergy supports producers, producers support consumers, and decomposers close the nutrient cycle.
1
Without a continuous energy input, producers cannot make carbon compounds and the food chains collapse.
2
If nutrients are removed, for example by harvesting timber, cycling is interrupted and productivity falls.
3
Low genetic diversity leaves a population unable to adapt if conditions change.
4
Climatic change beyond tolerance limits forces species to migrate or face extinction.
5
Human activities are now changing climate faster than many species can adapt.
Part 3 of 4Mesocosms
Mesocosms
Definition
- Definition A mesocosm is an enclosed experimental system that simulates part of a natural ecosystem under controlled conditions.
Advantage
- Advantage All factors but one can be held constant, so the effect of the variable, such as nutrient level, can be studied clearly.
Limitation
- Limitation Enclosure and control make a mesocosm less realistic than a real ecosystem, though larger ones improve realism.
Lab design
- Lab design Use a transparent container, include autotrophs and small primary consumers, and avoid secondary consumers.
Larger mesocosms
- Larger mesocosms Bigger enclosures that allow mixing and more interactions are more realistic, though they are costlier and harder to control.
| Type of mesocosm | Used to study |
|---|---|
| Land-based water tank | Sewage pollution in ponds |
| Underwater enclosure | Warming or CO₂ effects on marine life |
| Greenhouse-style building | Carbon movement in a forest |
Part 4 of 4Exam Checklist & Tips
4.10.1 – Key Points for the Exam
- Ecosystem stability The tendency of an ecosystem to resist change and keep its structure and function.
- Genetic diversity The number of different alleles of genes in a population.
- Mesocosm A controlled model ecosystem used to test the effects of changing factors.
- Tolerance limits The range of an environmental factor within which a species can survive.
Common Mistakes
- Equating stable with unchanging; stable ecosystems still undergo evolution and small fluctuations.
- Including top predators in a small mesocosm, where there is too little energy to support them.
- Saying biodiversity alone determines stability without mentioning cycling and energy supply.
- Treating mesocosm results as identical to real ecosystems.
Last updated:
\n