Ecology fundamentals — ecosystem types, food chains, nutrient cycles, and ecological succession — form the conceptual backbone of Environment & Ecology for UPSC. These concepts underlie all higher topics.
Ecosystem Types
| Type | Characteristics | Examples |
|---|---|---|
| Tropical Rainforest | Highest biodiversity; warm & wet; multi-layered canopy; rapid nutrient cycling | Amazon, Western Ghats, NE India |
| Grassland / Savanna | Seasonal rainfall; grasses dominant; large herbivores; fire-maintained | African savanna, Indian grasslands |
| Desert | <250 mm annual rain; extreme temps; xerophytes (CAM metabolism); high evaporation | Thar (India), Sahara, Atacama |
| Wetland | Transitional between aquatic and terrestrial; high productivity; "kidneys of the earth"; carbon sink | Chilika, Sundarbans, Keoladeo |
| Marine | Largest biome on Earth; photic zone (0–200m); abyssal zone; coral reefs most diverse marine ecosystem | Indian Ocean, coral reefs |
| Freshwater | Rivers, lakes, ponds; limnology; lentic (still) vs lotic (flowing) | Ganga, Wular lake |
| Estuary / Mangrove | Where freshwater meets saltwater; highly productive; nursery for fish; protects coasts from erosion | Sundarbans (largest mangrove) |
Food Chain and Trophic Levels
- Producers (T1): plants, algae, phytoplankton — fix solar energy via photosynthesis
- Primary Consumers (T2): herbivores (deer, rabbit, grasshoppers)
- Secondary Consumers (T3): small carnivores (frogs, small fish)
- Tertiary Consumers (T4): top predators (tigers, eagles, sharks)
- Decomposers: bacteria, fungi — break down dead organic matter; recycle nutrients
10% Energy Rule (Lindeman): Only ~10% of energy transfers from one trophic level to the next; rest lost as heat
Ecological Pyramids
| Pyramid Type | Always Upright? | Exception |
|---|---|---|
| Pyramid of Numbers | Not always | Inverted in tree ecosystem (1 tree supports many insects) |
| Pyramid of Biomass | Usually upright | Inverted in aquatic ecosystems (phytoplankton < zooplankton biomass at any moment) |
| Pyramid of Energy | Always upright | Never inverted; energy always decreases up the chain |
Biogeochemical Cycles
| Cycle | Key Facts |
|---|---|
| Carbon Cycle | Carbon reservoir: atmosphere (CO₂), oceans (dissolved), lithosphere (fossil fuels, limestone); photosynthesis absorbs CO₂; respiration + combustion releases; Oceans = largest carbon sink |
| Nitrogen Cycle | N₂ fixation (Rhizobium in legume roots; Azotobacter free-living; lightning); nitrification; denitrification; Haber process (industrial); atmosphere 78% N₂ |
| Phosphorus Cycle | No gaseous phase (sedimentary cycle); weathering of rocks; phosphate in soil → plants → animals → decomposers → soil; slow cycling |
| Water Cycle | Evaporation → condensation → precipitation → runoff/infiltration; transpiration; 97.5% saltwater; only 2.5% freshwater (70% in glaciers) |
| Sulphur Cycle | Volcanic eruptions + fossil fuel combustion → SO₂ → acid rain (H₂SO₄); weathering releases sulphate |
Ecological Succession
- Primary succession: starts on bare/lifeless substrate (bare rock, new volcanic island); pioneer species = lichens on rock
- Secondary succession: on disturbed area with existing soil (after fire, flood); faster than primary
- Sere: the entire sequence of communities from pioneer to climax
- Climax community: stable, self-sustaining final community; determined by climate
- Hydrosere: succession in water body → eventually terrestrial; pond → marsh → swamp → scrubland → forest
Key: Energy pyramid is always upright. Biomass pyramid inverted in aquatic ecosystems. 10% energy rule. Phosphorus cycle = sedimentary (no atmospheric phase). Rhizobium fixes N₂ in legumes. Lichens = pioneer on rock.