Introduction
An ecosystem is a complex network where living (biotic) and non-living (abiotic) components interact, enabling energy flow and material recycling. From forests to oceans, ecosystems sustain life through intricate processes like photosynthesis, food chains, and biogeochemical cycles.
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This guide explores:
Energy flow: How sunlight powers ecosystems via producers and consumers.
Food chains vs. webs: Trophic levels and their roles.
Biogeochemical cycles: Recycling of water, carbon, and nitrogen.
Terrestrial vs. aquatic ecosystems: Key differences and examples.
Whether you're a student or nature enthusiast, understanding ecosystems is key to appreciating ecological balance.
What Is an Ecosystem?
An ecosystem is a biological community of interacting organisms and their physical environment. It includes:
Biotic components: Plants, animals, microbes.
Abiotic components: Sunlight, water, soil, temperature.
Examples:
A pond (self-contained natural ecosystem).
An aquarium (human-made model ecosystem).
Energy Flow in Ecosystems
The Sun as the Ultimate Source
Only 1–2% of sunlight is used for photosynthesis by autotrophs (e.g., plants, algae).
This energy converts into chemical energy (carbohydrates), fueling heterotrophs (consumers).
Energy Transfer Efficiency
10% Rule: Only ~10% of energy passes to the next trophic level.
Producers (plants) → Primary consumers (herbivores) → Secondary consumers (carnivores).
Example:
Sun → Grass → Deer → Tiger → Decomposers (fungi).
Food Chains and Webs
Types of Food Chains
Grazing Food Chain: Starts with autotrophs (e.g., plants).
Detritus Food Chain: Begins with decaying matter (e.g., fungi breaking down dead leaves).
Food Webs
Most ecosystems feature interconnected food chains, forming complex webs. For instance, a single species (like a bear) can be both a primary (berry-eater) and secondary (fish-eater) consumer.
Ecological Pyramids
| Pyramid Type | Description | Example |
|---|---|---|
| Numbers | Count of organisms at each trophic level | Few trees → Many insects → Few birds |
| Biomass | Total dry weight of organisms | Inverted in oceans (tiny phytoplankton support large whales). |
| Energy | Always upright; energy decreases upward | 1000 kcal (plants) → 100 kcal (deer) → 10 kcal (tiger) |
Biogeochemical Cycles
The Nitrogen Cycle
Nitrogen Fixation: Bacteria convert atmospheric nitrogen (N₂) into ammonia (NH₃).
Nitrification: Ammonia → Nitrites → Nitrates (usable by plants).
Assimilation: Plants absorb nitrates to make proteins.
Denitrification: Bacteria return nitrogen to the atmosphere.
Human Impact: Fertilizers add excess nitrogen, disrupting natural cycles.
Other Key Cycles
Carbon Cycle: Photosynthesis and respiration balance CO₂ levels.
Water Cycle: Evaporation, condensation, and precipitation sustain ecosystems.
Ecological Succession
Primary vs. Secondary Succession
Primary: Colonization of lifeless areas (e.g., volcanic rock) by pioneer species (lichens).
Secondary: Recovery after disturbances (e.g., forest fires).
Climax Communities
Stable, mature ecosystems (e.g., old-growth forests) with high biodiversity and biomass.
Types of Ecosystems
Terrestrial Ecosystems
| Type | Features | Example |
|---|---|---|
| Forests | High rainfall, dense trees | Amazon Rainforest |
| Grasslands | Dominated by grasses; seasonal droughts | African Savanna |
| Deserts | <25 cm annual rainfall; sparse vegetation | Sahara Desert |
Aquatic Ecosystems
| Type | Features | Example |
|---|---|---|
| Marine | Saltwater; covers 71% of Earth | Pacific Ocean |
| Freshwater | Lakes, rivers, wetlands | Mississippi River |
Key Limiting Factors:
Terrestrial: Water availability.
Aquatic: Light (depth) and nutrient levels.
Key Takeaways
| Concept | Key Insight |
|---|---|
| Energy Flow | Sun → Producers → Consumers (10% transfer efficiency). |
| Food Webs | Complex interactions stabilize ecosystems. |
| Biogeochemical Cycles | Recycle essential elements (N, C, H₂O). |
| Succession | Ecosystems evolve toward climax communities. |
Conclusion
Ecosystems thrive on energy flow, nutrient cycles, and species interactions. Understanding these processes helps us protect biodiversity and address challenges like climate change.
Dive Deeper: Download the full PDF for detailed case studies and ecosystem models!
FAQ
Q: Why is only 10% of energy passed to the next trophic level?
A: Most energy is lost as heat or used for metabolism (e.g., movement, growth).
Q: How do humans disrupt the nitrogen cycle?
A: Overusing fertilizers increases soil nitrates, causing algal blooms in water bodies.
Q: What’s the difference between a food chain and a food web?
A: Food chains are linear; webs show interconnected chains for resilience.
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