Ecology – Study Notes for Meghalaya Patwari / Lekhpal
(General Awareness & Current Affairs)
Exam Focus – IIT‑JEE style depth, precise definitions, derivations, key formulas, “tricky points” that frequently appear in competitive exams, and a hard practice question to sharpen conceptual understanding.
1. What is Ecology?
| Term | Definition |
|---|---|
| Ecology | The scientific study of interactions between organisms and their environment (both biotic and abiotic). |
| Ecosystem | A community of living organisms plus the non‑living components (air, water, soil, minerals) that interact as a functional unit. |
| Biotic | Living components (plants, animals, microbes). |
| Abiotic | Non‑living components (temperature, light, soil, water, nutrients). |
2. Levels of Ecological Organization
| Level | Description | Example |
|---|---|---|
| Individual | Single organism. | A particular tiger in Meghalaya. |
| Population | Group of individuals of the same species in a region. | All deer in a reserve. |
| Community | All populations of different species in a region. | Forest fauna & flora. |
| Ecosystem | Community + abiotic environment. | Hill forest + soil, water, climate. |
| Biome | Large‑scale ecosystem with characteristic climate and vegetation. | Tropical rainforest, temperate forest. |
| Biosphere | All ecosystems on Earth. | Global planet. |
Key Trick – Populations are not the same as communities. A community is a group of populations.
3. Energy Flow in Ecosystems
3.1 Food Chains & Food Webs
- Primary Producers (autotrophs) convert light to chemical energy via photosynthesis.
- Primary Consumers (herbivores) eat producers.
- Secondary & Tertiary Consumers are higher‑trophic‑level carnivores.
- Decomposers (bacteria, fungi) recycle nutrients.
Tricky Point – A food web is a network of multiple overlapping food chains; a food chain is a linear sequence of trophic transfers.
3.2 Efficiency & Losses
- Transfer Efficiency ≈ 10 % between trophic levels.
- Energy Losses: Heat (≈60‑70 %), metabolic respiration, unconsumed matter.
4. Primary Productivity
4.1 Gross Primary Productivity (GPP)
GPP = Total amount of CO₂ fixed by photosynthesis per unit area per unit time.
[ \text{GPP} = \frac{\text{ΔC}_{\text{fixed}}}{\text{Area} \times \text{Time}} ]
4.2 Net Primary Productivity (NPP)
NPP = GPP – Respiration (R).
[ \boxed{\text{NPP} = \text{GPP} - R} ]
- Respiration includes both plant (autotrophic) and microbial (heterotrophic) respiration.
- Units: g C m⁻² yr⁻¹ or MJ m⁻² yr⁻¹.
Tricky Point – In many exam questions, students confuse Gross with Net. Remember: Net is what remains after subtracting plant respiration.
4.3 Biomass vs. Productivity
- Biomass – The total mass of living organisms in an ecosystem.
- Productivity – The rate of biomass production.
Tip – Biomass is a static quantity; productivity is a dynamic measure.
5. Biogeochemical Cycles
| Element | Cycle | Key Processes |
|---|---|---|
| Carbon | Photosynthesis → Respiration → Decomposition → CO₂ exchange | GPP, NPP, respiration, fossil fuel combustion |
| Nitrogen | Fixation → Nitrification → Assimilation → Denitrification | Biological N₂ fixation, microbial nitrification, plant uptake, NO₃⁻ release |
| Water | Evaporation → Condensation → Precipitation | Hydrologic cycle, groundwater recharge |
| Phosphorus | Weathering → Uptake → Sedimentation → Erosion | Mineral weathering, plant uptake, sediment deposition |
Tricky Point – Nitrogen is inorganic in the atmosphere (N₂) but only a few organisms fix it into bio‑available forms (NH₃, NO₃⁻).
6. Ecological Succession
| Succession | Description | Typical Time Scale |
|---|---|---|
| Primary | Starts on lifeless substrates (volcano, glacier). | Hundreds–thousands of |