Ecosystem

Key Concepts

Ecosystem Structure and Function

An ecosystem is a functional unit of nature where living organisms interact among themselves and with their physical environment.

Categories: Terrestrial (forest, grassland, desert) and Aquatic (pond, lake, wetland, river, estuary).
Stratification: Vertical distribution of different species occupying different levels (e.g., trees → shrubs → herbs).
Key Aspects: Productivity, Decomposition, Energy flow, and Nutrient cycling.

Productivity

Primary Production: Amount of biomass or organic matter produced per unit area by plants during photosynthesis.

NPP vs GPP Net Primary Productivity (NPP) is the actual biomass available to consumers after the plants have met their own respiratory needs (GPP - R).

Gross Primary Productivity (GPP): Total rate of production of organic matter.
Net Primary Productivity (NPP): GPP minus respiration losses (R). NPP = GPP - R. It is the biomass available for heterotrophs.
Secondary Productivity: Rate of formation of new organic matter by consumers.
Global NPP: ~170 billion tons. Oceans contribute only 55 billion tons despite covering 70% of Earth's surface.

Decomposition

Breakdown of complex organic matter into inorganic substances (CO2, H2O, nutrients).

Detritus: Raw material (dead leaves, bark, animal remains).
Steps:
1. Fragmentation: Detritivores (e.g., earthworm) break detritus into smaller particles.
2. Leaching: Water-soluble nutrients move down into the soil.
3. Catabolism: Bacterial and fungal enzymes degrade detritus into simpler inorganic substances.
4. Humification: Formation of dark, amorphous humus (resistant to microbes, nutrient reservoir).
5. Mineralisation: Release of inorganic nutrients from humus.
Factors: Faster if detritus is rich in Nitrogen/Sugars; slower if rich in Lignin/Chitin. Warm and moist environments favour decomposition.

Energy Flow

PAR: Photosynthetically Active Radiation (< 50% of incident solar radiation).

10 Per Cent Law Only 10% of the energy is transferred from one trophic level to the next, while 90% is lost as heat or used for metabolic processes.

First Law of Thermodynamics: Energy is transferred, not created or destroyed.
Second Law of Thermodynamics: Energy is lost as heat at each transfer (increasing disorder).
10 Per Cent Law: Only 10% of energy is transferred to the next trophic level.
Food Chains:
- Grazing Food Chain (GFC): Producer → Herbivore → Carnivore.
- Detritus Food Chain (DFC): Begins with dead organic matter. Major conduit in terrestrial ecosystems.
Food Web: Natural interconnection of food chains.

Ecological Pyramids

Express relationship between organisms at different trophic levels in terms of number, biomass, or energy.

Inverted Pyramid of Biomass In aquatic ecosystems (the sea), the pyramid of biomass is often inverted because the biomass of fishes far exceeds that of the phytoplankton supporting them.

Pyramid of Number: Usually upright (except for a big tree supporting many insects).
Pyramid of Biomass: Usually upright; Inverted in sea (phytoplankton biomass < fish biomass).
Pyramid of Energy: Always upright; energy is lost at each step.
Limitations: Does not account for same species in multiple trophic levels, assumes simple food chains, and ignores saprophytes.

Key Concepts

An ecosystem is a functional unit of nature where living organisms interact among themselves and with their physical environment.

Categories: Terrestrial (forest, grassland, desert) and Aquatic (pond, lake, wetland, river, estuary).

Stratification: Vertical distribution of different species occupying different levels (e.g., trees → shrubs → herbs).

Key Aspects: Productivity, Decomposition, Energy flow, and Nutrient cycling.

Primary Production: Amount of biomass or organic matter produced per unit area by plants during photosynthesis.

NPP vs GPP Net Primary Productivity (NPP) is the actual biomass available to consumers after the plants have met their own respiratory needs (GPP - R).

Gross Primary Productivity (GPP): Total rate of production of organic matter.

Net Primary Productivity (NPP): GPP minus respiration losses (R). NPP = GPP - R. It is the biomass available for heterotrophs.

Secondary Productivity: Rate of formation of new organic matter by consumers.

Global NPP: ~170 billion tons. Oceans contribute only 55 billion tons despite covering 70% of Earth's surface.

Breakdown of complex organic matter into inorganic substances (CO2, H2O, nutrients).

Detritus: Raw material (dead leaves, bark, animal remains).

Steps:

Fragmentation: Detritivores (e.g., earthworm) break detritus into smaller particles.
Leaching: Water-soluble nutrients move down into the soil.
Catabolism: Bacterial and fungal enzymes degrade detritus into simpler inorganic substances.
Humification: Formation of dark, amorphous humus (resistant to microbes, nutrient reservoir).
Mineralisation: Release of inorganic nutrients from humus.

Factors: Faster if detritus is rich in Nitrogen/Sugars; slower if rich in Lignin/Chitin. Warm and moist environments favour decomposition.

PAR: Photosynthetically Active Radiation (< 50% of incident solar radiation).

10 Per Cent Law Only 10% of the energy is transferred from one trophic level to the next, while 90% is lost as heat or used for metabolic processes.

First Law of Thermodynamics: Energy is transferred, not created or destroyed.

Second Law of Thermodynamics: Energy is lost as heat at each transfer (increasing disorder).

10 Per Cent Law: Only 10% of energy is transferred to the next trophic level.

Food Chains:

Grazing Food Chain (GFC): Producer → Herbivore → Carnivore.
Detritus Food Chain (DFC): Begins with dead organic matter. Major conduit in terrestrial ecosystems.

Food Web: Natural interconnection of food chains.

Express relationship between organisms at different trophic levels in terms of number, biomass, or energy.

Inverted Pyramid of Biomass In aquatic ecosystems (the sea), the pyramid of biomass is often inverted because the biomass of fishes far exceeds that of the phytoplankton supporting them.

Pyramid of Number: Usually upright (except for a big tree supporting many insects).

Pyramid of Biomass: Usually upright; Inverted in sea (phytoplankton biomass < fish biomass).

Pyramid of Energy: Always upright; energy is lost at each step.

Limitations: Does not account for same species in multiple trophic levels, assumes simple food chains, and ignores saprophytes.

Ecosystem

Ecosystem

Key Concepts

Ecosystem Structure and Function

Productivity

Decomposition

Energy Flow

Ecological Pyramids

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Ecosystem

Ecosystem

Key Concepts

Ecosystem Structure and Function

Productivity

Decomposition

Energy Flow

Ecological Pyramids

On this page