1. What is an Ecosystem?
An ecosystem is a dynamic complex of plant, animal, and microorganism communities and their non-living environment interacting as a functional unit.
2. Structure of an Ecosystem
The structure of an ecosystem refers to its composition and the way its components are arranged.
A. Biotic (Living) Components
| Category | Description | Examples |
|---|---|---|
| Producers (Autotrophs) | Organisms that make their own food using sunlight or chemical energy | Green plants, algae, phytoplankton, chemosynthetic bacteria |
| Consumers (Heterotrophs) | Organisms that obtain energy by consuming other organisms | Animals, most bacteria, fungi |
| • Primary consumers | Herbivores that eat producers | Zooplankton, rabbits, deer, grasshoppers |
| • Secondary consumers | Carnivores that eat primary consumers | Frogs, spiders, small fish |
| • Tertiary consumers | Top carnivores that eat secondary consumers | Hawks, lions, sharks |
| Decomposers | Break down dead organic matter and waste, recycling nutrients | Bacteria, fungi, detritivores (earthworms, millipedes) |
Biotic Components
B. Abiotic (Non-living) Components
- Physical factors: sunlight, temperature, wind, water currents
- Chemical factors: soil composition, water chemistry, salinity, pH, nutrients (N, P, K)
- Climatic factors: rainfall, humidity, atmospheric gases
C. Spatial Structure
- Stratification: Vertical layering (e.g., forest canopy, understory, forest floor)
- Zonation: Horizontal patterns due to environmental gradients (e.g., intertidal zones)
- Species diversity and distribution
3. Functions of an Ecosystem
A. Energy Flow
Energy enters the ecosystem through producers (photosynthesis) and flows unidirectionally through food chains and food webs.
- Sun → Producers → Primary consumers → Secondary consumers → Tertiary consumers
- Only about 10% of energy is transferred from one trophic level to the next (10% rule).
- Represented by ecological pyramids: pyramid of energy, biomass, numbers.
Energy Flow Pyramid
B. Nutrient Cycling (Biogeochemical Cycles)
Materials are recycled within the ecosystem in closed loops.
- Carbon cycle
- Nitrogen cycle
- Phosphorus cycle
- Water (hydrological) cycle
- Oxygen cycle
C. Ecological Succession
Orderly change in community structure over time.
- Primary succession: Starts on bare rock or new land (e.g., after volcanic eruption)
- Secondary succession: Occurs after disturbance in existing community (e.g., after fire)
- Leads to climax community (stable end stage)
Primary Succession
D. Homeostasis and Regulation
- Self-regulating mechanisms maintain balance
- Feedback loops (positive and negative)
- Population control through predation, competition, disease
4. Types of Ecosystems
- Terrestrial: Forests, grasslands, deserts, tundra
- Aquatic:
- Freshwater: ponds, lakes, rivers, wetlands
- Marine: oceans, coral reefs, estuaries
- Man-made: agroecosystems, aquariums, urban parks
Summary
Ecosystems have a definite structure (biotic + abiotic components arranged in trophic levels and spatial patterns) and perform vital functions (energy flow, nutrient cycling, succession, and self-regulation) that maintain life on Earth and provide essential ecosystem services to humanity.