Ecology — Ecosystems and Food Webs
Components of an Ecosystem
An ecosystem is a community of living organisms interacting with their non-living environment as a system.
Biotic components (living):
- Producers (autotrophs): plants, algae, phytoplankton — convert sunlight to food via photosynthesis
- Consumers (heterotrophs): primary (herbivores), secondary (carnivores eating herbivores), tertiary (carnivores eating carnivores)
- Decomposers: bacteria and fungi — break down dead organic matter and return nutrients to soil
Abiotic components (non-living): Temperature, light, water, soil, air, minerals.
Energy Flow — 10% Law
Energy flows through an ecosystem in one direction (sun → producers → consumers). Only about 10% of energy is transferred to each successive trophic level. The rest is lost as heat.
This is why food chains rarely have more than 4–5 levels — by the 5th level, barely any energy remains.
Trophic levels: Level 1 = Producers; Level 2 = Primary consumers; Level 3 = Secondary consumers; Level 4 = Tertiary consumers.
Nutrient Cycles
Carbon cycle: CO₂ absorbed by plants → eaten by animals → released through respiration, decomposition, combustion, and volcanic activity.
Nitrogen cycle: Atmospheric N₂ → fixed by nitrogen-fixing bacteria (Rhizobium in root nodules) → absorbed by plants → consumed by animals → returned to soil by decomposers → denitrifying bacteria convert back to N₂.
Water cycle: Evaporation → condensation → precipitation → surface runoff and groundwater recharge → evapotranspiration → repeat.
Biodiversity
India's Biodiversity Status
India covers only 2.4% of the world's land but supports:
- ~7–8% of recorded species
- ~45,000 plant species (7% of world flora)
- ~91,000 animal species
- 4 of the world's 36 biodiversity hotspots
India's 4 biodiversity hotspots: 1. Eastern Himalayas 2. Western Ghats and Sri Lanka 3. Indo-Burma region 4. Sundaland (Nicobar Islands component)
Tamil Nadu's Biodiversity
Tamil Nadu has the highest number of flowering plant species and reptiles among Indian states.
Key protected areas:
- Nilgiri Biosphere Reserve: First biosphere reserve in India (1986). Covers parts of Tamil Nadu, Kerala, Karnataka. Includes Mudumalai Tiger Reserve, Anamalai Tiger Reserve, Kalakad-Mundanthurai Tiger Reserve.
- Gulf of Mannar Marine National Park: India's first marine biosphere reserve. Coral reefs, dugong, sea cows.
- Vedanthangal Bird Sanctuary: One of the oldest bird sanctuaries in Asia (1858). Located near Chennai. Home to painted storks, cormorants, spoonbills.
- Pulicat Lake: Second largest brackish water lagoon in India. Important for flamingoes.
Threats to Biodiversity
- Habitat loss (deforestation, urbanisation, agriculture)
- Invasive alien species (Lantana, Prosopis juliflora in TN forests)
- Overexploitation (poaching, overfishing)
- Pollution
- Climate change
IUCN Red List categories: Extinct → Extinct in the Wild → Critically Endangered → Endangered → Vulnerable → Near Threatened → Least Concern.
Climate Change
Greenhouse Gases and Global Warming
Main greenhouse gases (by warming contribution): 1. Water vapour (H₂O) — natural 2. Carbon dioxide (CO₂) — from fossil fuels, deforestation 3. Methane (CH₄) — from livestock, rice paddies, landfills 4. Nitrous oxide (N₂O) — from agriculture, fertilisers 5. Fluorinated gases (HFCs, PFCs, SF₆) — from industrial processes
Key numbers:
- Pre-industrial CO₂: ~280 ppm
- Current CO₂ (2024): ~422 ppm (highest in 800,000 years)
- Paris Agreement goal: limit warming to 1.5°C above pre-industrial levels
- India's NDC commitment: achieve net-zero by 2070, 50% power from renewables by 2030
Impacts of climate change:
- Sea level rise (thermal expansion + glacier melt) — threatens coastal Tamil Nadu, Chennai, delta regions
- Erratic monsoon patterns — affects agriculture and water security in TN
- Increased frequency of extreme events — cyclones in Bay of Bengal, Chennai floods (2015)
- Coral bleaching — Gulf of Mannar reefs affected
- Crop yield decline — rice and wheat yields projected to fall 6–10% by 2050
International Climate Agreements
| Agreement | Year | Key Point |
|---|---|---|
| UN Framework Convention on Climate Change (UNFCCC) | 1992 | Framework treaty; all major nations |
| Kyoto Protocol | 1997 | Binding emission targets for developed nations |
| Paris Agreement | 2015 | All nations; voluntary NDCs; 1.5°C goal |
| Glasgow Climate Pact (COP26) | 2021 | Phase-down of coal; 2030 methane pledge |
| Dubai COP28 | 2023 | First global stocktake; transition away from fossil fuels |
Pollution
Air Pollution
Major air pollutants:
- Particulate matter (PM2.5, PM10): from vehicles, construction, agriculture burning
- Carbon monoxide (CO): incomplete combustion — reduces oxygen-carrying capacity of blood
- Sulphur dioxide (SO₂): from coal power plants — causes acid rain (pH < 5.6)
- Nitrogen oxides (NOₓ): from vehicles — contribute to smog and acid rain
- Ozone (O₃) at ground level: secondary pollutant — lung irritant
National Air Quality Index (AQI) categories: Good → Satisfactory → Moderate → Poor → Very Poor → Severe.
Water Pollution
Key sources: industrial effluents, agricultural run-off (pesticides, fertilisers), sewage, oil spills.
Eutrophication: Excessive nutrients (nitrogen, phosphorus) from agriculture run-off → algal blooms → oxygen depletion → fish death. Affects Tamil Nadu's Veeranam Lake, Krishnagiri reservoir.
Water pollution standards: Bureau of Indian Standards sets drinking water quality norms. Central Pollution Control Board (CPCB) monitors water quality.
Soil Pollution
Caused by: pesticides (DDT, endosulfan), heavy metals (lead, cadmium, mercury), industrial waste.
Endosulfan controversy in Tamil Nadu: Aerial spraying on cashew plantations in Kasaragod (Kerala border areas) caused neurological disorders, reproductive defects, cancer in communities. Endosulfan banned in India in 2011.
Environmental Laws and Bodies
Key Indian Environmental Laws
| Act | Year | Significance |
|---|---|---|
| Wildlife Protection Act | 1972 | Protects wild animals, plants; lists endangered species; Tiger Reserves |
| Water (Prevention and Control of Pollution) Act | 1974 | Established CPCB and SPCBs |
| Air (Prevention and Control of Pollution) Act | 1981 | Controls air pollution |
| Environment Protection Act | 1986 | Umbrella act post-Bhopal; empowers central government |
| Forest Conservation Act | 1980 | Diversion of forest land requires central approval |
| Biological Diversity Act | 2002 | Implements CBD; establishes National Biodiversity Authority (NBA) |
| Coastal Regulation Zone (CRZ) Notification | 1991, revised 2019 | Regulates development along coastlines |
National Biodiversity Authority (NBA) — headquartered in Chennai, Tamil Nadu. Regulates access to biological resources and traditional knowledge.
Pollution Control Bodies
- Central Pollution Control Board (CPCB): National body; publishes AQI, water quality data.
- Tamil Nadu Pollution Control Board (TNPCB): State body; monitors industries, issues consents, enforces standards.
Disaster Management
Types of Disasters
Natural disasters:
- Cyclones (Bay of Bengal cyclone season: October–December affects Tamil Nadu's coast)
- Floods (Chennai floods 2015 — ₹1 lakh crore damage; heaviest November rainfall in 100 years)
- Drought (Tamil Nadu depends on northeast monsoon; periodic failures cause water crisis)
- Earthquakes (Killari 1993, Bhuj 2001 — TN has moderate seismic risk)
- Tsunamis (2004 Indian Ocean Tsunami devastated Tamil Nadu coast — 8,000+ deaths in TN, particularly Nagapattinam)
Man-made disasters: Industrial accidents (Bhopal gas tragedy 1984 — methyl isocyanate leak, 3,000+ immediate deaths), fires, oil spills, chemical leaks.
Disaster Management Framework in India
Disaster Management Act, 2005 — Established National Disaster Management Authority (NDMA).
Three-tier structure: 1. National level: NDMA (PM as chairperson) → formulates national policy 2. State level: SDMA (CM as chairperson) → implements state plan 3. District level: DDMA (District Collector as CEO) → first responder coordination
National Disaster Response Force (NDRF): 16 battalions deployed across India for rapid response. Headquartered at Ghaziabad (UP). NDRF teams were deployed in Chennai 2015 floods and Cyclone Fani 2019.
Sendai Framework 2015–2030: Global framework for disaster risk reduction (DRR). Seven global targets including: substantially reduce mortality, economic losses, and damage to critical infrastructure due to disasters.
Cyclone Preparedness in Tamil Nadu
Tamil Nadu has one of the longest coastlines in India (1,076 km) and faces cyclones almost every year during October–December.
- Tamil Nadu State Disaster Management Authority (TNSDMA): Coordinates state-level response.
- Early warning systems: IMD cyclone warnings at 72 hours, 48 hours, 24 hours, 3 hours. Colour-coded alerts: Yellow (watch) → Orange (alert) → Red (warning).
- Cyclone shelters: Tamil Nadu has ~1,000+ cyclone shelters along the coast.
- Notable cyclones affecting TN: Cyclone Vardah (2016, Chennai), Cyclone Gaja (2018, Nagapattinam-Thanjavur), Cyclone Michaung (2023, Chennai-Nellore coast).
Board Exam Tips
- Environment and ecology questions in Group I prelims typically focus on biodiversity hotspots, key protected areas in Tamil Nadu, climate agreements, and disaster management institutions.
- Tamil Nadu-specific facts (Western Ghats, Nilgiri Biosphere, Gulf of Mannar, NBA headquarters in Chennai) are frequently asked.
- The 10% energy law in food chains is a standard 1-mark MCQ.
- NDMA, NDRF, and the three-tier disaster structure are common institutional questions.
- Climate agreement years: Kyoto = 1997, Paris = 2015. The goal (1.5°C) and India's net-zero year (2070) are directly asked.