Ecosystem

1. Ecosystem Structure, Stratification & Biomass States

A. Concept & Types of Ecosystem

• Term: Coined by A.G. Tansley. Functional unit of nature where living organisms interact among themselves and with their surrounding physical environment. Varies in size from a small pond to a large forest or ocean. Global ecosystem = entire biosphere.
• Classification:• Terrestrial (Natural): Forest, Grassland, Desert.

  • Aquatic (Natural): Pond, Lake, Wetland, River, Estuary.

  • Man-made / Anthropogenic: Crop fields, Aquarium. High productivity, low biodiversity, simple food chains, requiring human assistance and unsustainable independently.

B. Components of Ecosystem

C. Standing State vs. Standing Crop

• Standing State: Amount of inorganic nutrients (N, P, Ca, etc.) present in the soil/ecosystem at any given time.
• Standing Crop: Total amount of living organic matter / biomass present in a unit area of an ecosystem at a given time. Expressed as fresh weight or dry weight (most reliable).

2. Ecosystem Productivity & Decomposition Process

A. Primary & Secondary Productivity

• Gross Primary Productivity (GPP): Rate of capture of solar energy or total rate of biomass production by producers during photosynthesis.
• Net Primary Productivity (NPP): Available biomass stored per unit time by producers for consumption by heterotrophs.$$\mathbf{\text{NPP} = \text{GPP} – \text{Respiration Loss (R)}}$$
• Secondary Productivity: Rate of formation of new organic matter by consumers.
• Units of Productivity: Biomass $= \text{g/m}^2/\text{yr}$; Energy $= \text{kcal/m}^2/\text{yr}$.

B. Ecosystem Productivity Levels

• High Productivity Ecosystems: Coral reefs, Tropical Rain Forests, Sugarcane fields, Estuaries.
• Average Productivity: Deciduous & Temperate forests, Maize/Wheat fields.
• Low Productivity Ecosystems: Grasslands, Deserts, Deep Oceans.

3. Steps of Decomposition & Rate Regulating Factors

A. 5 Sequential Steps of Decomposition

Physical and chemical breakdown of dead organic matter (Detritus = dead plant/animal remains, fecal matter) into simple inorganic nutrients:

1. 1. Fragmentation: Physical breakdown of detritus into smaller particles by detritivores (Earthworms, Termites, Ants).
2. 2. Catabolism: Enzymatic degradation of simple organic matter into inorganic molecules by decomposers (Saprophytic Bacteria & Fungi).• Polysaccharides $\to$ Glucose $\to$ $\text{C, N, O}$.

   • Proteins $\to$ Amino acids $\to$ $\text{C, N}$.

3. 3. Leaching: Water-soluble inorganic nutrients percolate down into soil horizons and precipitate as unavailable salts (Immobilization).
4. 4. Humification: Leads to accumulation of a dark-coloured, amorphous, acidic, colloidal substance called Humus.• Humus is extremely resistant to microbial action (undergoes decomposition at an extremely slow rate), rich in lignin & cellulose, and serves as a nutrient reservoir.
5. 5. Mineralization: Slow degradation of humus by specific microbes releasing inorganic nutrients ($\text{N, P, K, Ca}$, etc.) back into the soil.

B. Factors Regulating Decomposition Rate

• Chemical Composition of Detritus:• Rich in Lignin & Chitin $\implies$ Rate of decomposition is SLOWER.

  • Rich in Nitrogen & Water-soluble substances (Sugars, Nucleic acids) $\implies$ Rate of decomposition is FASTER.

• Climatic Conditions:• Warm ($>25^\circ\text{C}$) & Moist Environment: Favors rapid decomposition.

  • Low Temperature ($<10^\circ\text{C}$) & Anaerobiosis (lack of $\text{O}_2$): Inhibits decomposition leading to organic matter build-up.

4. Energy Flow Dynamics & Grazing Food Chains (GFC)

A. Energy Flow & Solar Radiation Spectrum

• Sun is the sole source of energy for all terrestrial and aquatic ecosystems on Earth (Except deep sea hydrothermal vents).
• Incident Solar Energy Breakdown:• Incident Solar Radiation $= 100\%$.

  • Photosynthetically Active Radiation (PAR, $400\text{–}700\text{ nm}$) $= \mathbf{<50\%}$.
  • Plants capture only $2\text{–}10\%$ of PAR (which equals $1\text{–}5\%$ of total incident solar radiation) for gross primary productivity.

  • Out of captured GPP, $20\%$ is lost in respiration, leaving $1.6\text{–}8\%$ PAR stored as Net Primary Productivity (NPP).

• Unidirectional Flow: Follows First Law of Thermodynamics. Energy flows strictly from Sun $\to$ Producers (Transducers) $\to$ Herbivores $\to$ Carnivores.

B. Grazing Food Chain (GFC) Examples