Ecology – Study Notes (INI CET Biology)
1. Simple Explanation
Ecology is the scientific study of how organisms interact with each other and with their physical environment.
It looks at all levels – from a single organism to entire biomes – and asks questions such as:
- How do species survive and reproduce?
- How does energy flow through an ecosystem?
- What happens when a species is removed or a climate changes?
2. Key Points
| Level | What It Is | Why It Matters | Example |
|---|---|---|---|
| Organism | A single living entity (plant, animal, microbe). | The basic unit of life that interacts with its environment. | A maple tree in a forest. |
| Population | Group of individuals of the same species in a given area. | Population dynamics (birth, death, migration) influence species persistence. | 200 deer in a national park. |
| Community | All populations of different species in one area. | Inter‑species interactions (predation, competition, mutualism). | Deer, wolves, oak trees, insects in a woodland. |
| Ecosystem | A community plus its non‑living (abiotic) components (soil, water, light). | Energy and nutrients move through ecosystems; they provide services. | Forest ecosystem: trees, soil, sunlight, rain. |
| Biome | A large geographic area with a characteristic climate and dominant vegetation. | Biomes differ in species composition and ecological processes. | Tropical rainforest, tundra, desert. |
| Biogeochemical Cycle | The movement of elements (C, N, P, etc.) through ecosystems. | Keeps ecosystems functioning and limits resource depletion. | Carbon cycle: plants → atmosphere → animals. |
| Energy Flow | One‑way transfer of energy from producers to consumers, then to decomposers. | Determines how many trophic levels can be supported. | Sun → plants → herbivores → carnivores. |
| Trophic Level | Rank in a food chain (producers, primary consumers, etc.). | Helps quantify energy transfer efficiency. | 1st trophic level: grass. |
| Food Web | Interconnected food chains in a community. | Shows redundancy and ecosystem resilience. | Grass → rabbit → fox → eagle. |
| Ecological Succession | Gradual change in community composition after a disturbance. | Predicts ecosystem development over time. | Pine forest → hardwood forest. |
| Biodiversity | Variety of life at genetic, species, and ecosystem levels. | Provides ecosystem stability and resilience. | Genetic diversity in crops. |
| Human Impact | Activities that alter ecosystems (deforestation, pollution, climate change). | Drives many ecological problems and conservation needs. | Plastic pollution in oceans. |
| Conservation Ecology | Managing and protecting ecosystems and biodiversity. | Ensures ecosystem services for future generations. | Protected marine reserves. |
3. Worked Example: Calculating Energy Transfer in a Simple Food Chain
Scenario:
A forest ecosystem has the following food chain:
- Sunlight → Green grass (producer)
- Grass → Grasshopper (primary consumer)
- Grasshopper → Frog (secondary consumer)
Assumptions:
- Grass captures 1000 kJ of solar energy per day.
- Only 10 % of the captured energy is converted into plant biomass (photosynthetic efficiency).
- Energy transfer efficiency between trophic levels is 10 % (typical value).
Step‑by‑Step:
| Trophic Level | Energy Captured (kJ/day) | Energy Available to Next Level (10%) | Energy Stored in Organisms (kJ/day) |
|---|---|---|---|
| 1. Producers (Grass) | 1000 kJ | 100 kJ | 100 kJ |
| 2. Primary Consumers (Grasshopper) | – | 10 kJ | 10 kJ |
| 3. Secondary Consumers (Frog) | – | 1 kJ | 1 kJ |
Interpretation
- Only 1 kJ of the original 1000 kJ reaches the frog each day.
- Because of the 10 % efficiency rule, the number of trophic levels that can be sustained is limited (classic “10 % rule”).
- This shows why top predators are fewer and why ecosystems need large areas to support them.
4. Quick Revision Summary (Bullet‑Point)
- Ecology: study of interactions among organisms and their environment.
- Levels: organism → population → community → ecosystem → biome.
- Key Processes: energy flow (10 % rule), biogeochemical cycles, succession.
- Food Webs: interconnected chains; show ecosystem resilience.
- Biodiversity: genetic, species, ecosystem; vital for stability.
- Human impacts: habitat loss, pollution, climate change → threats to biodiversity.
- Conservation: protected areas, restoration, sustainable use.
Remember: In any ecosystem, energy moves one way (from sun to producers to consumers to decomposers), while nutrients cycle repeatedly. The efficiency of energy transfer determines how many organisms can be supported at each trophic level.