Ecology and Ecosystem Dynamics

🟢 Lite — Quick Review (1h–1d)

Rapid summary for last-minute revision before your exam.

Ecology — Key Facts for Sri Lanka A/L Examination

Key Definitions:

Term	Definition
Ecology	Study of interactions between organisms and environment
Population	Group of same species in an area
Community	All populations in an area
Ecosystem	Community + physical environment
Biome	Large geographic area with similar climate and organisms
Biosphere	Living zone of Earth

Levels of Organization (smallest to largest): $$\text{Organism} \rightarrow \text{Population} \rightarrow \text{Community} \rightarrow \text{Ecosystem} \rightarrow \text{Biome} \rightarrow \text{Biosphere}$$

Biotic vs Abiotic Factors:

Biotic (Living)	Abiotic (Non-living)
Plants, animals, fungi	Temperature, light, water
Decomposers	Soil, air, minerals
Predators, parasites	pH, salinity

⚡ A/L Exam Tip: Sri Lanka is in the Tropical Rainforest Biome - high temperature, high rainfall year-round,多层 canopy structure!

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🟡 Standard — Regular Study (2d–2mo)

Standard content for students with a few days to months.

Ecology — Detailed Study Guide

Food Chains and Food Webs

Food Chain (linear):

Producers → Primary Consumers → Secondary Consumers → Tertiary Consumers
   ↓              ↓                   ↓                    ↓
  Plants        Herbivores        Small carnivores     Top predators

Trophic Levels:

Level	Position	Examples
1st	Producers	Green plants, algae
2nd	Primary consumers	Herbivores
3rd	Secondary consumers	Small carnivores
4th	Tertiary consumers	Top predators
Decomposers	Detritivores	Fungi, bacteria

Ecological Pyramids:

Pyramid	Shows	Usually
Numbers	Number of organisms	Tapers (one tree → many insects)
Biomass	Dry weight at each level	Tapers
Energy	Energy at each level	Always tapers

⚡ Important: Energy decreases at each level (only ~10% transfers) because:

1. Not all organism is eaten
2. Some food is undigested
3. Much energy lost as heat (respiration)

Nutrient Cycling

Carbon Cycle:

Atmosphere (CO₂)
      ↓ photosynthesis
Producers → Primary consumers → Secondary consumers
      ↑         respiration             ↑
      └────── decomposition ←────────────┘
              (CO₂ released)

Nitrogen Cycle:

N₂ (atmosphere)
   ↓ N₂ fixation (Rhizobium in legumes)
NH₃ (ammonia)
   ↓ Nitrification (bacteria)
NO₃⁻ (nitrate) → absorbed by plants
   ↓ Assimilation into plants
Organic N → Animals
   ↓ Decomposition
NH₃ → nitrification → NO₃⁻
   ↓ Denitrification (bacteria)
N₂ ← atmosphere

Phosphorus Cycle:

• No atmospheric component
• Weathering of rocks → phosphate
• Plants absorb PO₄³⁻
• Through food chain
• Decomposition returns to soil
• Some lost to ocean sediments

Ecosystem Types in Sri Lanka

Natural Ecosystems:

Ecosystem	Location	Features
Rainforests	Central highlands, Sinharaja	Dense canopy, high biodiversity
Dry forests	Northern, eastern plains	Deciduous, monsoon-adapted
Mangroves	Coastal areas	Salt-tolerant, tidal
Wetlands	marshes, reservoirs	Seasonal flooding
Montane forests	Above 1500m	Cloud forests, mist

Artificial Ecosystems:

Ecosystem	Examples
Agricultural	Rice paddies, tea estates
Reservoirs	Tanks, hydroelectric dams
Urban	Cities, towns

Sri Lanka’s Forest Coverage (Current):

• ~ 29% forest cover (2020)
• Natural forests: ~ 17%
• Plantations: ~ 12%
• Endemic species: High in Sri Lanka (56 endemic freshwater fish, many endemic butterflies)

⚡ A/L Important: Sri Lanka is one of 36 global biodiversity hotspots! The Western Ghats and Sri Lanka hotspot is critically important for conservation.

Population Ecology

Population Growth Patterns:

Growth Type	Characteristics	Formula
Exponential	Unlimited resources, J-shaped	dN/dt = rN
Logistic	Limited resources, S-shaped	dN/dt = rN(1-N/K)
Carrying capacity (K)	Maximum sustainable population	-

Population Interactions:

Interaction	Species 1	Species 2	Example
Competition	-	-	Two predators competing
Predation	+	-	Lion and zebra
Parasitism	+	-	Tapeworm and human
Commensalism	+	0	Epiphytes on trees
Mutualism	+	+	Bees and flowers

⚡ Gause’s Competitive Exclusion Principle: Two species competing for the same resources cannot coexist indefinitely - one will outcompete the other.

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🔴 Extended — Deep Study (3mo+)

Comprehensive coverage for students on a longer study timeline.

Ecology — Complete Notes for A/L Sri Lanka

Ecological Succession

Primary Succession:

• Starts with bare rock/sand
• No soil present
• Very slow (100s-1000s of years)
• Examples: Volcanic islands, sand dunes

Secondary Succession:

• Starts with disturbed area that had soil
• Faster than primary (10s-100s of years)
• Examples: Abandoned farmland, after fire

Succession Stages:

Bare area → Pioneer species (lichens, mosses) → Grasses → Shrubs → Early forest → Climax community

Climax Community:

• Final, stable community
• Most efficient energy use
• In Sri Lanka: Tropical rainforest (wet zones), dry forest (dry zones)

Biodiversity and Conservation

Levels of Biodiversity:

Level	Definition	Example
Genetic	Variety within a species	Different varieties of rice
Species	Variety of species	All plant species in Sri Lanka
Ecosystem	Variety of habitats	Rainforest + mangroves

Biodiversity Hotspots:

• Criteria: >1500 endemic plant species, <30% original habitat
• Western Ghats & Sri Lanka is one of 36 global hotspots
• Sri Lanka: 21% endemic plants, 16% endemic vertebrates

Threats to Biodiversity:

Threat	Description	Sri Lankan Example
Habitat loss	Deforestation, agriculture	Sinharaja fragmentation
Overexploitation	Hunting, logging	Giant freshwater fish decline
Pollution	Chemicals, runoff	Temple tank pollution
Invasive species	Outcompete natives	Lantana camara invasion
Climate change	Temperature rise	Coral bleaching

Conservation Methods:

Method	Description	Sri Lankan Example
Protected areas	National parks, reserves	Yala, Wilpattu, Sinharaja
Ex-situ	Zoos, botanical gardens	Peradeniya Botanic Gardens
Legislation	Laws protecting species	Fauna & Flora Protection Ordinance
Community-based	Local involvement	Veddas traditional knowledge

Sri Lankan Protected Areas:

• 26 National Parks
• 64 Strict Natural Reserves
• 3 UNESCO World Heritage Sites (including Sinharaja)
• 1 Biosphere Reserve (Bundala)

⚡ A/L Important: The IUCN Red List categorizes species by extinction risk:

• Extinct (EX)
• Critically Endangered (CR)
• Endangered (EN)
• Vulnerable (VU)
• Near Threatened (NT)
• Least Concern (LC)

Environmental Issues

Climate Change Impacts on Sri Lanka:

• Temperature increase: ~0.9°C since 1900
• Sea level rise threatening coastal areas
• Changes in monsoon patterns
• Coral bleaching (Indian Ocean bleaching events)
• Shift in agricultural zones

Pollution Types:

Type	Source	Impact
Air	Vehicles, industry	Respiratory problems
Water	Sewage, chemicals	Eutrophication
Soil	Pesticides, heavy metals	Contamination
Noise	Traffic, construction	Wildlife disruption

Sustainable Development:

• Meeting needs without compromising future generations
• Sri Lanka’s “Haritha Lanka” (Green Lanka) initiatives
• Renewable energy expansion (hydro, solar, wind)
• Organic agriculture promotion

GCE A/L Sri Lanka Past Paper Tips

Common Structured Questions:

1. “Explain the carbon cycle in an ecosystem” (10 marks)
2. “Describe the process of ecological succession in a named ecosystem” (12 marks)
3. “What is meant by a food web? Why is it more realistic than a food chain?” (8 marks)
4. “Discuss the threats to biodiversity in Sri Lanka” (15 marks)
5. “Explain the nitrogen cycle with reference to named microorganisms” (12 marks)

Diagram Questions:

1. Draw and label a pyramid of energy (6 marks)
2. Draw a labeled diagram of the nitrogen cycle (10 marks)
3. Draw a food web from a named Sri Lankan ecosystem (8 marks)

Case Study Questions:

• Sinharaja Forest Conservation
• Yala National Park ecosystem
• Wetland conservation (Bundala)
• Mangrove conservation

⚡ A/L Strategy: For Sri Lankan ecology questions, always use local examples (Sinharaja, Yala, tank cascade systems, mangrove ecosystems) to demonstrate understanding of local context!

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