This topic covers the basic concepts of ecosystems, including the components of an ecosystem, types of ecosystems (terrestrial, aquatic, etc.), and the interactions between biotic and abiotic factors.
Introduction to Ecosystems
Key concepts, components, and processes
1. What Is an Ecosystem?
| Definition |
Explanation |
| Ecosystem |
A community of living organisms (plants, animals, microbes) interacting with one another and with the non‑living (abiotic) environment in a defined area. |
| Scope |
Can be as small as a pond or as large as a forest biome; the boundaries are set by the researcher’s purpose, not by a hard physical line. |
| Dynamic |
Ecosystems are constantly changing through energy flow, material cycles, and species interactions. |
2. Major Components
| Biotic (Living) |
Abiotic (Non‑living) |
| Producers (autotrophs) – plants, algae, cyanobacteria that convert solar energy into chemical energy (photosynthesis). |
Sunlight – primary energy source. |
| Consumers – herbivores, carnivores, omnivores, and decomposers that obtain energy by eating other organisms. |
Water – medium for biochemical reactions, transport, and habitat. |
| Decomposers – fungi, bacteria, detritivores that break down dead material, releasing nutrients back to the system. |
Soil/ substrate – provides minerals, structure, and habitat for many organisms. |
| Microorganisms – bacteria, archaea, protists that drive nutrient cycling (e.g., nitrogen fixation). |
Temperature & Climate – affect metabolic rates, distribution of species. |
| Keystone species – organisms that have a disproportionately large effect on ecosystem structure (e.g., sea otters in kelp forests). |
Atmospheric gases – CO₂, O₂, N₂, etc., involved in photosynthesis, respiration, and nitrogen cycle. |
3. Energy Flow
- Solar Radiation → Primary Production
- Photosynthetic organisms capture sunlight, converting it to chemical energy (glucose).
- Trophic Levels
- 1st level: Producers (autotrophs).
- 2nd level: Primary consumers (herbivores).
- 3rd level: Secondary consumers (carnivores that eat herbivores).
- 4th level: Tertiary/Quaternary consumers (top predators).
- Energy Loss
- ~90 % of energy is lost as heat at each trophic transfer (Second Law of Thermodynamics).
- Only ~10 % passes to the next level → pyramidal shape of energy pyramids.
- Food Webs
- Interconnected feeding relationships; more realistic than simple linear food chains.
4. Matter (Nutrient) Cycling
| Cycle |
Core Process |
Key Organisms/Agents |
| Carbon |
Photosynthesis (CO₂ → organic C) → Respiration (organic C → CO₂) → Decomposition → Fossilization (long‑term storage) |
Plants, animals, microbes, oceans |
| Nitrogen |
N₂ fixation → Nitrification → Assimilation → Ammonification → Denitrification (return to N₂) |
Nitrogen‑fixing bacteria, nitrifying bacteria, plants, fungi |
| Phosphorus |
Weathering → Uptake by plants → Consumption → Decomposition → Sedimentation (slow return) |
Soil microbes, plants, aquatic organisms |
| Water (Hydrologic) Cycle |
Evaporation → Condensation → Precipitation → Runoff/ |
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