Environmental Ecology and Ecosystem Dynamics

🟢 Lite — Quick Review (1h–1d)

Rapid summary for last-minute revision before your exam.

Environmental Ecology — Key Facts for Sri Lanka A/L Examination

Ecosystem Components:

Component	Role	Examples
Producers	Convert solar energy to chemical energy	Photosynthetic plants, algae
Consumers	Obtain energy by eating other organisms	Herbivores, carnivores, omnivores
Decomposers	Break down dead organic matter	Bacteria, fungi
Abiotic factors	Non-living environmental factors	Light, temperature, water, soil

Food Chain Levels: Producers → Primary Consumers → Secondary Consumers → Tertiary Consumers → Decomposers

Sri Lankan Examples:

• Tropical rainforest food chain in Sinharaja
• Coral reef ecosystem in Gulf of Mannar
• Mangrove ecosystem in Puttalam lagoon

⚡ A/L Exam Tip: Always distinguish between food chains (linear) and food webs (interconnected) — food webs are more realistic representations of ecosystem energy flow!

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🟡 Standard — Regular Study (2d–2mo)

Standard content for students with a few days to months.

Environmental Ecology — Detailed Study Guide

Ecological Pyramids

Types of Pyramids:

Pyramid Type	Shows	Shape	Limitation
Numbers	Number of organisms per trophic level	Can be inverted	Large producers vs small consumers
Biomass	Total dry weight at each level	Usually upright	Seasonal variations
Energy	Energy content (kcal/m²/year)	Always upright	—

10% Rule of Ecology: Only approximately 10% of energy is transferred from one trophic level to the next. The remaining 90% is used in metabolic processes and lost as heat.

Formula for Energy Transfer: $$E_{n+1} = E_n \times 0.10$$

Where $E_n$ = Energy at trophic level n

Biogeochemical Cycles

Water Cycle (Hydrological Cycle):

Precipitation → Surface runoff → Infiltration →
Transpiration by plants → Evaporation → Condensation → Precipitation

Carbon Cycle:

• Photosynthesis: $6CO_2 + 6H_2O \rightarrow C_6H_{12}O_6 + 6O_2$
• Respiration: $C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + ATP$
• Key reservoirs: Atmosphere, ocean, fossil fuels, biomass

Nitrogen Cycle:

Process	Description	Organism
Nitrogen fixation	N₂ → NH₃	Azotobacter, Rhizobium
Nitrification	NH₃ → NO₂⁻ → NO₃⁻	Nitrosomonas, Nitrobacter
Denitrification	NO₃⁻ → N₂	Pseudomonas

Phosphorus Cycle:

• No gaseous form
• Weathering of rocks → soil → plants → animals → decomposition → soil
• Limited by phosphate availability

Ecosystem Types in Sri Lanka

Classification:

Ecosystem	Location	Characteristics
Tropical Rainforest	Sinharaja, Knuckles	High rainfall (>2500mm), diverse species
Dry Zone	North-central	<1750mm rainfall, thorny vegetation
Mangrove	Coastal wetlands	Salt-tolerant species, nursery function
Coral Reef	Coastal marine	High biodiversity, fragile
Montane	Central highlands	Cloud forests, endemic species

Threats to Sri Lankan Ecosystems:

Threat	Impact	Conservation Status
Habitat fragmentation	Population isolation	Sinharaja UNESCO site
Invasive species	Native species displacement	Mahaweli development
Pollution	Water quality decline	mangroves under threat
Climate change	Coral bleaching	50% reef decline

⚡ A/L PYQ: “Explain how energy flows through an ecosystem using the 10% rule” Answer: Energy is transferred from producers to consumers, with only ~10% passed to each successive level. 90% is lost as heat through respiration, meaning tertiary consumers receive very little energy.

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🔴 Extended — Deep Study (3mo+)

Comprehensive coverage for students on a longer study timeline.

Environmental Ecology — Complete Notes for A/L Sri Lanka

Population Ecology

Population Growth Models:

Model	Formula	Pattern
Exponential	$N_t = N_0 e^{rt}$	J-shaped curve
Logistic	$N_t = \frac{KN_0 e^{rt}}{K + N_0(e^{rt} - 1)}$	S-shaped curve (sigmoid)

Where $r$ = intrinsic growth rate, $K$ = carrying capacity

Population Interactions:

Interaction	Species 1	Species 2	Example
Competition	−	−	Two bird species eating same insects
Predation	+	−	Lion-zebra relationship
Parasitism	+	−	Tapeworm-human
Mutualism	+	+	Bee-flower pollination
Commensalism	+	0	Barnacle-whale

Ecological Succession

Primary Succession:

• Starts on bare rock/sterile substrate
• Pioneer species: Lichens → Mosses → Grasses → Shrubs → Climax community
• Time required: 100s-1000s of years

Secondary Succession:

• Starts on previously inhabited soil
• Faster progression: Grasses → Shrubs → Climax community
• Example: Abandoned agricultural land in Sri Lanka

Climax Community:

• Final, stable community
• In Sri Lanka: Tropical rainforest (wet zone), thorn forest (dry zone)

Conservation Biology

Principles:

1. Biodiversity Hotspots: Areas with high species richness and endemism
   • Sri Lanka is part of Western Ghats & Sri Lanka Hotspot
2. Minimum Viable Population: Smallest population that can survive
3. Edge Effects: Changes at habitat boundaries

In-Situ Conservation:

Method	Sri Lankan Example
National Parks	Yala, Wilpattu, Horton Plains
Nature reserves	Ritigala Strict Nature Reserve
Protected forests	Sinharaja Conservation Zone

Ex-Situ Conservation:

Method	Purpose
Seed banks	Germplasm storage (Maha Nakhara, Gannoruwa)
Botanical gardens	Peradeniya, Ratnapura
Tissue culture	Orchid conservation

Sri Lanka’s Endemic Species (Important for exam):

Species	Common Name	Status
Panthera pardus kotiya	Sri Lankan leopard	Endangered
Elephas maximus maximus	Sri Lankan elephant	Endangered
Presbytis senex	Purple-faced langur	Endangered
Ornithoptera triangularis	Sri Lanka birdwing	Protected

Biodiversity Act No. 29 of 1988 — governs protection of native species

Environmental Impact Assessment (EIA)

EIA Process in Sri Lanka:

1. Screening (determine if EIA required)
2. Scoping (identify key issues)
3. Impact prediction and evaluation
4. Mitigation measures
5. Reporting and review
6. Decision making and monitoring

Projects Requiring EIA:

• Major infrastructure (roads, dams, ports)
• Industrial establishments
• Mining operations
• Tourism development

⚡ A/L Strategy: Questions on Sri Lankan ecology are frequently asked. Know the specific ecosystems, conservation areas, and endemic species — these make your answers stand out!

⚡ Essay Preparation:

1. “Discuss the importance of biodiversity conservation in Sri Lanka” (20 marks)
2. “Explain the process of ecological succession in Sri Lankan ecosystems” (15 marks)
3. “Describe the threats to Sri Lankan ecosystems and conservation measures” (12 marks)

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