I. ECOSYSTEM — OVERVIEW & STRUCTURE
A DEFINITION & BASICS
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| FEATURE | DETAIL |
|---|---|
| Term coined by | A.G. Tansley ⭐⭐ |
| Definition | Functional unit of nature where living organisms interact among themselves AND with the surrounding physical environment ⭐ |
| Size range | Small pond → Large forest → Sea; entire biosphere = global ecosystem |
| Two components | Biotic (living organisms) + Abiotic (physical / chemical factors) |
⚡ EXAM TRAP: NEET 2016
Term 'Ecosystem' coined by A.G. Tansley.
B CATEGORIES OF ECOSYSTEMS
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| CATEGORY | EXAMPLES |
|---|---|
| Terrestrial | Forest, Grassland, Desert |
| Aquatic | Pond, Lake, Wetland, River, Estuary |
| Man-made | Crop field, Aquarium ⭐ |
⚡ EXAM TRAP: NEET 2016
Cropland = man-made ecosystem; characterised by least genetic diversity and absence of self-regulation.
⚡ EXAM TRAP: NEET 2017
Maximum biomass is found in Forest Ecosystem.
C STRUCTURAL FEATURES
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| FEATURE | DETAIL |
|---|---|
| Species composition | Identification & enumeration of plant & animal species |
| Stratification | Vertical distribution of different species occupying different levels ⭐⭐ |
🔑 Stratification in a forest: TOP LAYER → Trees | 2nd LAYER → Shrubs | BOTTOM LAYER → Herbs & Grasses
⚡ EXAM TRAP: NEET 2015
Stratification = vertical distribution of species at different levels.
D FOUR MAJOR COMPONENTS OF ECOSYSTEM FUNCTIONING
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| # | COMPONENT |
|---|---|
| 1 | Productivity |
| 2 | Decomposition |
| 3 | Energy flow |
| 4 | Nutrient cycling |
⚡ EXAM TRAP: NEET 2012
Four components — Productivity, Decomposition, Energy flow, Nutrient cycling.
E POND ECOSYSTEM — A SIMPLE EXAMPLE
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| COMPONENT | DETAIL |
|---|---|
| Type | Simple, self-sustainable, shallow aquatic ecosystem ⭐ |
| Abiotic | Water with dissolved inorganic & organic substances; rich soil deposit at bottom; solar input; temperature; day-length |
| Autotrophic (Producers) | Phytoplankton, some Algae, Floating, Submerged & Marginal plants (at edges) ⭐ |
| Consumers | Zooplankton, free-swimming organisms, bottom-dwelling forms |
| Decomposers | Bacteria, Fungi, Flagellates (abundant at bottom) ⭐ |
| Energy flow | Unidirectional — towards higher trophic levels; dissipated as heat ⭐ |
II. PRODUCTIVITY
A PRIMARY PRODUCTION
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| FEATURE | DETAIL |
|---|---|
| Definition | Amount of biomass or organic matter produced per unit area over a time period by plants during photosynthesis ⭐ |
| Expressed as (production) | Weight: g m−2 OR Energy: kcal m−2 |
| Productivity | Rate of biomass production = g m−2 yr−1 or kcal m−2 yr−1 ⭐ |
⚡ EXAM TRAP: NEET 2020, 2022
Primary production = biomass produced by plants during photosynthesis; expressed as g m−2 or kcal m−2.
⚡ EXAM TRAP: NEET 2025
The unit of productivity of an ecosystem is (kcal m−2) yr−1. Productivity is a RATE, so the per-year term is essential. g m−2 and kcal m−2 alone are units of production, not productivity.
⚡ EXAM TRAP: NEET 2025
The rate of production of organic matter during photosynthesis is GROSS primary productivity (GPP), not net primary productivity.
B GPP vs NPP
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| FEATURE | GPP (GROSS PRIMARY PRODUCTIVITY) | NPP (NET PRIMARY PRODUCTIVITY) |
|---|---|---|
| Definition | Rate of production of organic matter during photosynthesis = total photosynthetic output ⭐ | Available biomass for consumption by heterotrophs (herbivores & decomposers) ⭐ |
| Formula | — | NPP = GPP – R ⭐⭐⭐ (R = Respiratory losses) |
| Relationship | GPP is always > NPP ⭐ | Always less than GPP |
⚡ EXAM TRAP: NEET 2015
GPP = total rate of organic matter production during photosynthesis.
⚡ EXAM TRAP: NEET 2021, 2023
NPP = GPP – R; available biomass for consumers.
⚡ EXAM TRAP: NEET 2020
GPP is always more than NPP.
⚡ EXAM TRAP: NEET 2026 (Match-the-list)
Productivity ↔ rate of biomass production; Net primary productivity ↔ GPP minus respiration losses; Gross primary productivity ↔ rate of production of organic matter during photosynthesis; Secondary productivity ↔ rate of formation of new organic matter by consumers.
C SECONDARY PRODUCTIVITY
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| FEATURE | DETAIL |
|---|---|
| Definition | Rate of formation of new organic matter by consumers (heterotrophs) ⭐ |
| Important | NOT by plants — by consumers |
⚡ EXAM TRAP: NEET 2012, 2013
Secondary productivity = rate of new organic matter formation by consumers.
D FACTORS AFFECTING PRIMARY PRODUCTIVITY
- Plant species inhabiting the area
- Nutrient availability
- Photosynthetic capacity of plants
- Environmental factors
E GLOBAL PRODUCTIVITY NUMBERS
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| PARAMETER | VALUE |
|---|---|
| Annual NPP of whole biosphere | ≈ 170 billion tons (dry weight) of organic matter ⭐ |
| Ocean productivity | Only ≈ 55 billion tons (despite covering ~70% of Earth surface) ⭐ |
| Land productivity | Remaining ≈ 115 billion tons |
III. DECOMPOSITION
A DEFINITION
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| FEATURE | DETAIL |
|---|---|
| Definition | Breakdown of complex organic matter into simple inorganic substances (CO2, water, nutrients) by decomposers ⭐ |
| Detritus | Dead remains of plants & animals (leaves, bark, flowers, dead animals, fecal matter) = raw material for decomposition ⭐ |
| Nature of process | Largely an oxygen-requiring (aerobic) process ⭐ |
⚡ EXAM TRAP: NEET 2026 (Match-the-list)
Decomposition ↔ breaking down of complex organic matter into inorganic substances; Detritus ↔ dead remains of plants and animals including fecal matter; Mineralisation ↔ release of inorganic nutrients by activity of microbes in soil; Humification ↔ accumulation of dark coloured amorphous colloidal substance.
B STEPS OF DECOMPOSITION
🔑 Correct order: FRAGMENTATION → LEACHING → CATABOLISM → HUMIFICATION → MINERALISATION
All steps (fragmentation, leaching, catabolism) operate simultaneously on detritus; Humification & Mineralisation occur during decomposition in the soil.
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| STEP | PROCESS | KEY DETAIL |
|---|---|---|
| 1. Fragmentation | Breakdown of detritus into smaller particles | By detritivores (e.g., Earthworm) ⭐⭐ |
| 2. Leaching | Water-soluble inorganic nutrients move down soil horizon | Get precipitated as unavailable salts ⭐ |
| 3. Catabolism | Bacterial & fungal enzymes degrade detritus | Into simple inorganic substances ⭐ |
| 4. Humification | Accumulation of dark-coloured amorphous substance called Humus ⭐⭐ | Highly resistant to microbial action; decomposes at extremely slow rate |
| 5. Mineralisation | Humus further degraded by microbes | Releases inorganic nutrients back into soil ⭐ |
⚡ EXAM TRAP: NEET 2013, 2022, 2023
Steps of decomposition — know order and details of each.
⚡ EXAM TRAP: NEET 2022
Fragmentation = by detritivores (earthworms).
C HUMUS — PROPERTIES
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| PROPERTY | DETAIL |
|---|---|
| Colour | Dark-coloured ⭐ |
| Nature | Amorphous ⭐ |
| Colloidal | Yes — serves as reservoir of nutrients ⭐ |
| Microbial resistance | Highly resistant to microbial action ⭐ |
| Decomposition rate | Extremely slow ⭐ |
🔑 Key distinction: Humus ≠ Mineralisation — Humus is the resistant intermediate; Mineralisation releases inorganic nutrients FROM humus.
D FACTORS AFFECTING DECOMPOSITION RATE
Chemical Composition of Detritus ⭐⭐
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| IF DETRITUS IS RICH IN... | RATE IS... |
|---|---|
| Lignin & Chitin | Slower ⭐⭐ (resistant substances) |
| Nitrogen & water-soluble substances (sugars) | Quicker ⭐⭐ |
⚡ EXAM TRAP: NEET 2020, 2022
Lignin & Chitin → slow decomposition; Nitrogen & Sugars → fast decomposition.
Climatic Factors (Most Important) ⭐⭐
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| FACTOR | DETAIL |
|---|---|
| Temperature | Most important regulator ⭐ |
| Soil moisture | Most important regulator ⭐ |
| Warm + Moist | Favours decomposition ⭐ |
| Low temperature + Anaerobiosis | Inhibits decomposition → causes build-up of organic materials ⭐ |
IV. ENERGY FLOW
A KEY PRINCIPLES
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| PRINCIPLE | DETAIL |
|---|---|
| Energy source | Sun = only source for all ecosystems (except deep-sea hydrothermal) ⭐ |
| Energy flow | Unidirectional — cannot be reversed or recycled ⭐⭐⭐ |
| PAR | Of incident solar radiation, < 50% is Photosynthetically Active Radiation ⭐ |
| Plants capture | Only 2–10% of PAR ⭐ |
| Thermodynamics | Ecosystems obey both First and Second Laws; need constant energy supply to counteract increasing disorderliness |
⚡ EXAM TRAP: NEET 2025
In an ecosystem there is a unidirectional flow of energy from the sun through producers to consumers. Ecosystems are NOT exempted from the second law of thermodynamics — they obey it and need a constant supply of energy.
⚡ EXAM TRAP: NEET 2025
The primary source of energy in an ecosystem is solar energy.
⚡ EXAM TRAP: RE-NEET 2026
Energy flow from producers to consumers is unidirectional, and the energy pyramid can never be inverted. The transfer of energy follows the 10 PER CENT law, not the 1 per cent law.
B PRODUCERS, CONSUMERS & DECOMPOSERS
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| CATEGORY | ALSO CALLED | ROLE |
|---|---|---|
| Producers | Autotrophs; Converters / Transducers ⭐ | Convert solar energy → chemical energy via photosynthesis |
| Primary Consumers | Herbivores | Feed on producers |
| Secondary Consumers | Primary carnivores | Feed on herbivores |
| Tertiary Consumers | Secondary / Top carnivores | Feed on primary carnivores |
| Decomposers | Saprotrophs; Osmotrophs ⭐ | Decompose dead bodies; secrete enzymes externally & absorb nutrients |
C FOOD CHAINS
Two Types ⭐⭐⭐
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| TYPE | BEGINS WITH | MAJOR CONDUIT IN | DETAIL |
|---|---|---|---|
| Grazing Food Chain (GFC) | Living plants (producers) ⭐ | Aquatic ecosystems ⭐ | Plants → Herbivores → Carnivores |
| Detritus Food Chain (DFC) | Dead organic matter (detritus) ⭐ | Terrestrial ecosystems ⭐ | Detritus → Detritivores → Decomposers |
🔑 Simple GFC: Grass (Producer) → Goat (Primary Consumer) → Man (Secondary Consumer)
🔑 In terrestrial ecosystems a much larger fraction of energy flows through DFC than GFC. DFC and GFC are connected at some levels; omnivores create food webs.
Food Web ⭐
Many interlinked food chains in an ecosystem = natural interconnections of food chains.
D TROPHIC LEVELS
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| TROPHIC LEVEL | ORGANISMS | EXAMPLES |
|---|---|---|
| T1 (1st) | Producers ⭐ | Grass, Phytoplankton, Trees |
| T2 (2nd) | Primary Consumers (Herbivores) ⭐ | Zooplankton, Grasshopper, Cow |
| T3 (3rd) | Secondary Consumers (Primary Carnivores) ⭐ | Birds, Fishes, Wolf |
| T4 (4th) | Tertiary Consumers (Top Carnivores) ⭐ | Man, Lion, Vulture |
🔑 Important: A given species may occupy more than one trophic level simultaneously. Example: Sparrow = T2 when eating seeds/fruits AND T3 when eating insects/worms.
⚡ EXAM TRAP: RE-NEET 2026
Herbivores are the primary consumers in a food chain — parasites, predators and carnivores are not.
E 10% LAW (Lindeman Efficiency)
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| FEATURE | DETAIL |
|---|---|
| Statement | Only 10% of energy is transferred from one trophic level to the next ⭐⭐ |
| 90% is | Lost as heat through respiration ⭐ |
| Proposed by | Lindeman |
| Consequence | Restricts the number of trophic levels in GFC |
⚡ EXAM TRAP: NEET 2014
10% Law — only 10% transferred to each successive trophic level.
⚡ EXAM TRAP: RE-NEET 2026
Transfer of energy between trophic levels follows the 10% law. The 1% law refers to the fraction of incident sunlight converted by producers into NPP and is a standing distractor.
Peacock Calculation (NEET 2014) ⭐⭐
🔑 Plant (20 J) → Mice (2 J) → Snake (0.2 J) → Peacock (0.02 J)
Reverse Calculation (NEET 2024 RE) ⭐⭐
🔑 If T4 = 1,000 J → T3 = 10,000 J (×10) → T2 = 1,00,000 J (×10) → T1 = 10,00,000 J (×10)
10% Law Calculation (NEET 2024) ⭐
🔑 If NPP of T1 = 100x → T2 = 10x (10%) → T3 = x (10%)
F DEEP SEA ECOSYSTEM
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| FEATURE | DETAIL |
|---|---|
| Primary producers | Chemosynthetic bacteria (at hydrothermal vents) ⭐ |
| Most animals | Detritivores ⭐ |
| Energy source | NOT sun — chemical energy from vent chemicals |
⚡ EXAM TRAP: NEET 2015, 2016
Deep sea — chemosynthetic bacteria as producers; most animals are detritivores.
V. ECOLOGICAL PYRAMIDS
A DEFINITION & STRUCTURE
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| FEATURE | DETAIL |
|---|---|
| Shape | Broad base, narrows towards apex |
| Base | Represents Producers (1st trophic level) ⭐ |
| Apex | Represents Tertiary / Top consumers ⭐ |
| Three types | Pyramid of Number, Pyramid of Biomass, Pyramid of Energy |
| Represent | Functional levels (trophic levels), NOT species ⭐⭐ |
⚡ EXAM TRAP: NEET 2021, 2020
Ecological pyramids represent functional levels; a species may occupy more than one trophic level.
B THREE TYPES — MASTER COMPARISON
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| PYRAMID TYPE | TERRESTRIAL | AQUATIC (SEA / OCEAN) | CAN IT BE INVERTED? |
|---|---|---|---|
| Pyramid of Number | Usually Upright ⭐ | — | Yes — Inverted in Tree ecosystem ⭐ |
| Pyramid of Biomass | Upright ⭐ | Generally Inverted ⭐⭐ | Yes (in aquatic) |
| Pyramid of Energy | ALWAYS Upright ⭐⭐⭐ | ALWAYS Upright ⭐⭐⭐ | NEVER — can NEVER be inverted ⭐⭐⭐ |
⚡ EXAM TRAP: NEET 2019, 2017, 2012
Inverted pyramid of biomass in sea/ocean (phytoplankton < zooplankton).
⚡ EXAM TRAP: NEET 2020, 2021
Pyramid of energy is ALWAYS upright; can NEVER be inverted.
⚡ EXAM TRAP: NEET 2020
Pyramid of number in grassland = upright.
⚡ EXAM TRAP: NEET 2026
Ecological pyramids are generally INVERTED for the pyramid of biomass in the sea. Pyramid of number in grassland, pyramid of biomass in grassland and pyramid of energy in a pond are all upright.
⚡ EXAM TRAP: RE-NEET 2026
The pyramid of energy can NEVER be inverted.
Grassland Ecosystem — Pyramid of Numbers ⭐
🔑 UPRIGHT: ~6 million plants (T1) → Many herbivores (T2) → Fewer carnivores (T3) → Only 3 top carnivores (T4)
Tree Ecosystem — Pyramid of Numbers ⭐
🔑 INVERTED AT BASE: Few large trees (T1) → Many insects (T2) → Fewer insect-eating birds (T3) → Even fewer raptors (T4)
Inverted Pyramid of Biomass (Sea) ⭐⭐
🔑 INVERTED: Small phytoplankton biomass (T1) < Large zooplankton biomass (T2) < Fish biomass (T3)
⚡ EXAM TRAP: NEET 2018
If Producer biomass (10 g) < Consumer biomass (60 g) → Inverted Pyramid of Biomass.
Pyramid of Energy ⭐⭐⭐
- Energy always decreases at successive trophic levels
- Some energy always lost as heat at each step
- Each bar = amount of energy per unit area per unit time (or annually)
- Producers convert only ~1% of sunlight energy into NPP
C STANDING CROP
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| FEATURE | DETAIL |
|---|---|
| Definition | Mass of living material (biomass) present at each trophic level at a particular time ⭐ |
| Measured as | Biomass (mass of living organisms) OR Number per unit area |
| Biomass expressed as | Fresh weight or Dry weight |
| More accurate | Dry weight measurement ⭐ |
⚡ EXAM TRAP: NEET 2015, 2012
Standing crop = biomass at a trophic level at a particular time; dry weight is more accurate.
D LIMITATIONS OF ECOLOGICAL PYRAMIDS
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| LIMITATION | DETAIL |
|---|---|
| Same species at multiple levels | Does not account for a species belonging to two or more trophic levels ⭐ |
| Simple food chain assumed | Does not accommodate food webs ⭐ |
| Saprophytes excluded | Decomposers have no space in the pyramid ⭐ |
⚡ EXAM TRAP: NEET 2024
Limitations — no food webs, no saprophytes, same species at multiple trophic levels.
VI. ECOLOGICAL SUCCESSION
A DEFINITION & KEY TERMS
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| TERM | DEFINITION |
|---|---|
| Ecological succession | Gradual & fairly predictable change in species composition of a given area over time ⭐ |
| Climax community | Community in near equilibrium with its environment = final stable stage ⭐ |
| Sere(s) | The entire sequence of communities that successively change in a given area ⭐ |
| Seral stages / Seral communities | The individual transitional communities during succession ⭐ |
⚡ EXAM TRAP: NEET 2015
Ecological succession = gradual, predictable change in species composition over time.
B TYPES OF SUCCESSION
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| TYPE | STARTS IN | SOIL PRESENT? | SPEED | EXAMPLES |
|---|---|---|---|---|
| Primary succession | Area where NO living organisms existed before ⭐ | No soil initially | Slower | Newly cooled lava, bare rocks, newly created pond |
| Secondary succession | Area where natural biotic communities have been destroyed ⭐ | Yes | Faster ⭐ | Flooded area, cut / burned forest |
⚡ EXAM TRAP: NEET 2015
Primary succession = no prior life; Secondary succession = soil present, faster.
C HYDRARCH vs XERARCH SUCCESSION
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| FEATURE | HYDRARCH | XERARCH |
|---|---|---|
| Starts in | Wet / Aquatic areas ⭐ | Dry areas ⭐ |
| Progresses from | Hydric → Mesic conditions ⭐ | Xeric → Mesic conditions ⭐ |
| Both ultimately lead to | Medium water conditions (Mesic) ⭐ — neither too dry nor too wet | |
D GENERAL PATTERN
🔑 SUCCESSION: Bare Area → Pioneer Species → Seral Stages → Climax Community
E PRIMARY SUCCESSION ON ROCKS (Xerarch)
🔑 Pioneer Species = LICHENS ⭐⭐⭐
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| STAGE | ORGANISMS | DETAIL |
|---|---|---|
| 1. Lichens (Pioneer) ⭐ | Crustose lichens | Secrete acids to dissolve rock → weathering & soil formation ⭐ |
| 2. Bryophytes | Mosses | Colonise small amounts of soil formed |
| 3. Herbs & Grasses | — | As soil accumulates |
| 4. Shrubs | — | — |
| 5. Trees | — | Stable climax forest community |
⚡ EXAM TRAP: NEET 2016
Pioneer species on rocks = Lichens; secrete acids → dissolve rock → soil formation.
F PRIMARY SUCCESSION IN WATER (Hydrarch)
🔑 Pioneer Species = PHYTOPLANKTON ⭐⭐
🔑 SEQUENCE: Phytoplankton (Pioneer) → Rooted Submerged plants → Rooted Floating Angiosperms → Free-floating plants → Reed Swamp → Marsh Meadow → Scrub → Trees → Forest (Climax)
G SUCCESSION SUMMARY
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| FEATURE | XERARCH (ROCKS) | HYDRARCH (WATER) |
|---|---|---|
| Pioneer | Lichens ⭐ | Phytoplankton ⭐ |
| Direction | Dry → Mesic | Wet → Mesic |
| Climax | Forest | Forest / Land |
VII. NUTRIENT CYCLING (BIOGEOCHEMICAL CYCLES)
A DEFINITION
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| FEATURE | DETAIL |
|---|---|
| Definition | Movement & exchange of nutrients between biotic and abiotic components ⭐ |
| Also called | Biogeochemical cycles ⭐ |
| Standing state | Amount of nutrients present in soil at any given time — varies with ecosystem type & season ⭐ |
⚡ EXAM TRAP: NEET 2021
Nutrient cycling = biogeochemical cycles = movement of nutrients between biotic & abiotic.
B TWO TYPES OF NUTRIENT CYCLES
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| TYPE | RESERVOIR | EXAMPLES |
|---|---|---|
| Gaseous cycle | Atmosphere / Hydrosphere ⭐ | Nitrogen cycle, Carbon cycle ⭐ |
| Sedimentary cycle | Earth crust (Rocks) ⭐ | Sulphur cycle, Phosphorus cycle ⭐ |
⚡ EXAM TRAP: NEET 2015, 2012
Gaseous (atmosphere) vs Sedimentary (earth crust); know examples of each.
C CARBON CYCLE
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| FEATURE | DETAIL |
|---|---|
| Carbon in organisms | Constitutes 49% of dry weight (next to water) ⭐ |
| Global carbon — Oceans | 71% dissolved in oceans ⭐ |
| Global carbon — Atmosphere | Only 1% of total global carbon ⭐ |
| Carbon fixed annually | 4 × 1013 kg through photosynthesis ⭐ |
| Cycling occurs through | Atmosphere, Ocean, Living & Dead organisms |
| Type | Gaseous cycle (reservoir = atmosphere) |
Human Impact ⭐
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| ACTIVITY | EFFECT |
|---|---|
| Deforestation + Fossil fuel burning | Significantly increased CO2 release into atmosphere ⭐ |
| Result | Influences carbon cycle → contributes to global warming ⭐ |
D PHOSPHORUS CYCLE
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| FEATURE | DETAIL |
|---|---|
| Natural reservoir | Rock (Earth crust) — in the form of phosphates ⭐⭐ |
| Type | Sedimentary cycle (reservoir = earth crust, NOT atmosphere) ⭐ |
| Weathering | Of rock → accelerates phosphorus cycle ⭐ |
| Animals obtain phosphorus | From plants |
| Decomposition | Waste & dead organisms decomposed by phosphate-solubilising bacteria → release phosphorus back into soil |
| Respiratory release | NO respiratory release of phosphorus into atmosphere (unlike carbon) ⭐⭐ |
| Atmospheric inputs (rainfall) | Much smaller than carbon inputs ⭐ |
| Exchange between organisms & environment | Negligible (very slow turnover) ⭐ |
⚡ EXAM TRAP: NEET 2022, 2013
Phosphorus reservoir = rock (earth crust); phosphates.
⚡ EXAM TRAP: NEET 2022
Weathering of rock accelerates phosphorus cycle.
⚡ EXAM TRAP: NEET 2015, 2012
Phosphorus cycle = sedimentary cycle (NOT gaseous).
E CARBON CYCLE vs PHOSPHORUS CYCLE — COMPARISON
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| FEATURE | CARBON CYCLE | PHOSPHORUS CYCLE |
|---|---|---|
| Type | Gaseous | Sedimentary |
| Reservoir | Atmosphere | Earth crust (Rocks) |
| Respiratory release | Yes (CO2) | No |
| Atmospheric inputs | Significant | Much smaller |
| Turnover | Faster | Very slow |
| Human impact | Deforestation + fossil fuels → ↑CO2 | Weathering accelerates cycle |
VIII. ECOSYSTEM SERVICES
A VALUATION
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| FEATURE | DETAIL |
|---|---|
| Pioneered by | Robert Constanza and colleagues ⭐ |
| Average price tag | US $33 trillion per year ⭐ |
| Comparison | Nearly double the global GNP of US $18 trillion ⭐ |
⚡ EXAM TRAP: NEET 2014
Robert Constanza put price tags on ecosystem services; $33 trillion/year.
B CONTRIBUTION TO TOTAL COST
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| SERVICE | CONTRIBUTION |
|---|---|
| Soil formation | ≈ 50% ⭐ (largest single contribution) |
| Recreation & Nutrient cycling | < 10% each |
| Climate regulation & Wildlife habitat | ≈ ~6% each |
C LIST OF ECOSYSTEM SERVICES
- Purification of air & water
- Mitigation of droughts & floods
- Cycling of nutrients
- Generation of fertile soil
- Pollination
- Waste treatment
- Pest control
- Biodiversity maintenance
IX. RAPID REVISION — KEY COMPARISON TABLES
TABLE 1: GPP vs NPP vs Secondary Productivity
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| FEATURE | GPP | NPP | SECONDARY PRODUCTIVITY |
|---|---|---|---|
| Produced by | Producers (plants) | Producers (plants) | Consumers |
| Formula | Total photosynthetic output | GPP – R | Rate of new organic matter by consumers |
| Includes respiratory losses? | Yes (included in total) | No (subtracted) | — |
| Available for consumption? | No (some used by plants) | Yes ⭐ | — |
| Relationship | GPP > NPP always | NPP < GPP always | — |
TABLE 2: GFC vs DFC
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| FEATURE | GRAZING FOOD CHAIN (GFC) | DETRITUS FOOD CHAIN (DFC) |
|---|---|---|
| Begins with | Living plants | Dead organic matter (detritus) |
| Major conduit in | Aquatic ecosystems | Terrestrial ecosystems |
| Organisms | Plants → Herbivores → Carnivores | Detritus → Detritivores → Decomposers |
| Connected to | DFC at some levels | GFC at some levels |
TABLE 3: Steps of Decomposition
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| STEP | PROCESS | AGENT / DETAIL |
|---|---|---|
| Fragmentation | Break into smaller pieces | Detritivores (Earthworm) |
| Leaching | Water-soluble nutrients go down | Precipitated as unavailable salts |
| Catabolism | Enzymatic degradation | Bacteria & Fungi |
| Humification | Humus accumulation | Dark, amorphous, resistant, colloidal |
| Mineralisation | Release of inorganic nutrients | From humus by microbes |
TABLE 4: Decomposition Rate Factors
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| FACTOR | FASTER | SLOWER |
|---|---|---|
| Chemical composition | Nitrogen, Sugars (water-soluble) | Lignin, Chitin |
| Climate | Warm + Moist | Cold + Anaerobic |
TABLE 5: Three Ecological Pyramids
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| PYRAMID | TERRESTRIAL | AQUATIC (SEA) | CAN BE INVERTED? |
|---|---|---|---|
| Number | Usually Upright | — | Yes (Tree ecosystem) |
| Biomass | Upright | Inverted | Yes (in aquatic) |
| Energy | ALWAYS Upright | ALWAYS Upright | NEVER |
TABLE 6: Primary vs Secondary Succession
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| FEATURE | PRIMARY | SECONDARY |
|---|---|---|
| Starting area | No prior life (bare) | Destroyed communities (soil present) |
| Speed | Slower | Faster |
| Examples | Lava, Bare rocks, New pond | Burned forest, Flooded area |
TABLE 7: Xerarch vs Hydrarch Succession
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| FEATURE | XERARCH | HYDRARCH |
|---|---|---|
| Starts in | Dry areas | Wet / Aquatic areas |
| Pioneer | Lichens | Phytoplankton |
| Progresses | Xeric → Mesic | Hydric → Mesic |
| Both lead to | Mesic conditions | |
TABLE 8: Gaseous vs Sedimentary Cycles
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| FEATURE | GASEOUS | SEDIMENTARY |
|---|---|---|
| Reservoir | Atmosphere / Hydrosphere | Earth crust (Rocks) |
| Examples | Carbon, Nitrogen | Phosphorus, Sulphur |
| Turnover | Relatively faster | Very slow |
TABLE 9: Key Numbers to Remember
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| PARAMETER | VALUE |
|---|---|
| PAR | < 50% of incident solar radiation |
| Plants capture of PAR | 2–10% |
| 10% Law | Only 10% energy transferred to next trophic level |
| 1% figure | Incident sunlight converted by producers into NPP |
| Annual NPP of biosphere | ~170 billion tons |
| Ocean productivity | ~55 billion tons |
| Carbon — Oceans | 71% of total global carbon |
| Carbon — Atmosphere | 1% of total global carbon |
| Carbon fixed annually | 4 × 1013 kg |
| Carbon in organisms | 49% of dry weight |
| Ecosystem services value | US $33 trillion/year |
| Global GNP | US $18 trillion |
| Soil formation contribution | ~50% of ecosystem services cost |
TABLE 10: Trophic Level Identification
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| ORGANISM | TROPHIC LEVEL |
|---|---|
| Grass / Phytoplankton | T1 (Producer) |
| Grasshopper / Zooplankton / Cow | T2 (Primary Consumer) |
| Frog / Small Fish / Wolf | T3 (Secondary Consumer) |
| Snake / Eagle / Lion | T4 (Tertiary Consumer) |
| Sparrow eating seeds | T2 |
| Sparrow eating insects | T3 |
| Man eating plants | T2 |
| Man eating chicken | T3 |
X. COMMON EXAM TRAPS — QUICK REFERENCE
CONSOLIDATED PYQ Q&A TABLE ⭐⭐⭐
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| TRAP / QUESTION | CORRECT ANSWER |
|---|---|
| Term 'Ecosystem' coined by? | A.G. Tansley |
| Ecosystem = ? | Functional unit of nature |
| Stratification = ? | Vertical distribution of species at different levels |
| Four components of ecosystem functioning? | Productivity, Decomposition, Energy flow, Nutrient cycling |
| Man-made ecosystems? | Crop field & Aquarium |
| Unit of productivity? | (kcal m−2) yr−1 ⭐⭐⭐ |
| g m−2 / kcal m−2 alone are units of? | Production — not productivity ⭐⭐⭐ |
| Primary production by whom? | Plants (during photosynthesis) |
| Rate of organic matter production in photosynthesis? | GPP (not NPP) ⭐⭐⭐ |
| Secondary productivity by whom? | Consumers (NOT plants) |
| GPP or NPP — which is greater? | GPP > NPP always |
| NPP formula? | GPP – R (R = respiratory losses) ⭐⭐⭐ |
| NPP = biomass available for whom? | Heterotrophs (herbivores & decomposers) |
| Productivity ↔ ? | Rate of biomass production ⭐⭐ |
| Secondary productivity ↔ ? | Rate of new organic matter formation by consumers ⭐⭐ |
| Annual NPP of biosphere? | ~170 billion tons |
| Ocean productivity? | ~55 billion tons (despite 70% surface area) |
| Detritus = ? | Dead remains of plants & animals including fecal matter ⭐⭐ |
| Decomposition ↔ ? | Complex organic matter → inorganic substances ⭐⭐ |
| Decomposition steps (order)? | Fragmentation → Leaching → Catabolism → Humification → Mineralisation |
| Fragmentation done by? | Detritivores (Earthworm) |
| Leaching = ? | Water-soluble nutrients go down; precipitated as unavailable salts |
| Catabolism in decomposition = ? | Bacterial/fungal enzymes degrade detritus |
| Humification ↔ ? | Accumulation of dark coloured amorphous colloidal substance ⭐⭐⭐ |
| Mineralisation ↔ ? | Release of inorganic nutrients by soil microbes ⭐⭐⭐ |
| Humus = same as mineralisation? | No — Humus is resistant intermediate; Mineralisation releases nutrients FROM humus |
| Decomposition — aerobic or anaerobic? | Largely aerobic |
| Decomposition slower with? | Lignin & Chitin |
| Decomposition faster with? | Nitrogen & water-soluble sugars |
| Most important climatic factors for decomposition? | Temperature & Soil moisture |
| Are ecosystems exempt from the 2nd law of thermodynamics? | No — they obey it ⭐⭐⭐ |
| Primary source of energy in an ecosystem? | Solar energy ⭐⭐ |
| Energy flow direction? | Unidirectional (cannot be reversed / recycled) ⭐⭐⭐ |
| Energy transfer follows which law? | 10% law (NOT 1% law) ⭐⭐⭐ |
| What does the 1% figure refer to? | Sunlight converted by producers into NPP ⭐⭐⭐ |
| PAR = what % of solar radiation? | < 50% |
| Plants capture what % of PAR? | 2–10% |
| Producers also called? | Autotrophs; Converters / Transducers |
| Decomposers also called? | Saprotrophs; Osmotrophs |
| GFC major in which ecosystem? | Aquatic |
| DFC major in which ecosystem? | Terrestrial |
| 10% Law proposed by? | Lindeman |
| Primary consumers are? | Herbivores ⭐⭐⭐ |
| Can one species occupy multiple trophic levels? | Yes (e.g., Sparrow) |
| Standing crop = ? | Biomass at a trophic level at a particular time |
| Biomass — fresh or dry weight more accurate? | Dry weight |
| Which pyramid is generally inverted? | Pyramid of biomass in the sea ⭐⭐⭐ |
| Pyramid of energy — always upright? | YES — ALWAYS; can NEVER be inverted ⭐⭐⭐ |
| Pyramid of energy in a pond? | Upright ⭐⭐⭐ |
| Pyramid of biomass in grassland? | Upright ⭐⭐ |
| Pyramid of number in tree ecosystem? | Inverted |
| Pyramid of number in grassland? | Upright |
| Saprophytes in pyramids? | NOT included (no space) |
| Limitations of ecological pyramids? | No food webs; no saprophytes; same species at multiple levels |
| Ecological succession = ? | Gradual, predictable change in species composition |
| Climax community = ? | Final stable stage in equilibrium with environment |
| Sere = ? | Entire sequence of successional communities |
| Primary succession starts in? | Bare / lifeless area (no prior organisms) |
| Secondary succession starts in? | Destroyed area with soil present |
| Which is faster — primary or secondary? | Secondary |
| Pioneer species on rocks? | Lichens |
| Pioneer species in water? | Phytoplankton |
| Lichens do what to rocks? | Secrete acids → dissolve rock → weathering & soil formation |
| Both Hydrarch & Xerarch lead to? | Mesic conditions |
| Nutrient cycling = ? | Biogeochemical cycles |
| Standing state = ? | Amount of nutrients in soil at any given time |
| Gaseous cycle reservoir? | Atmosphere |
| Sedimentary cycle reservoir? | Earth crust (Rocks) |
| Carbon cycle — gaseous or sedimentary? | Gaseous |
| Phosphorus cycle — gaseous or sedimentary? | Sedimentary |
| Carbon = what % of dry weight? | 49% |
| Carbon in oceans? | 71% of total global carbon |
| Carbon in atmosphere? | 1% |
| Carbon fixed annually? | 4 × 1013 kg |
| Phosphorus reservoir? | Rock (earth crust) — as phosphates |
| Weathering accelerates which cycle? | Phosphorus cycle |
| Respiratory release of phosphorus? | No (unlike carbon) |
| Robert Constanza — what did he do? | Put price tags on ecosystem services |
| Ecosystem services value? | US $33 trillion/year |
| Largest contribution to ecosystem services cost? | Soil formation (~50%) |
| Deep sea producers? | Chemosynthetic bacteria |
| Deep sea consumers? | Mostly detritivores |
| Human activities affecting carbon cycle? | Deforestation + Fossil fuel burning → ↑CO2 → Global warming |