Chapter 12: Ecosystem

Introduction to Ecosystems

• Ecosystem: Functional unit of nature, composed of living organisms interacting with each other and their environment
• Varies in size (small pond to large forest/sea)
• Biosphere seen as a global ecosystem
• Divided into terrestrial and aquatic ecosystems
  • Terrestrial: Forest, grassland, desert
  • Aquatic: Pond, lake, wetland, river, estuary
  • Man-made ecosystems: Crop fields, aquariums

Structure and Function of Ecosystems

• Components: Abiotic (non-living) and biotic (living)
• Interaction leads to a physical structure unique to each ecosystem
• Species composition: Identification and enumeration of plant/animal species
• Stratification: Vertical distribution of species (e.g., trees, shrubs, grasses)
• Functions:
  • Productivity
  • Decomposition
  • Energy flow
  • Nutrient cycling

Pond Example

• Abiotic: Water with dissolved substances, soil
• Biotic: Autotrophs (phytoplankton, algae), consumers (zooplankton), decomposers (fungi, bacteria)
• Functions:
  • Conversion of inorganic to organic material
  • Movement of energy towards higher trophic levels
  • Energy dissipation as heat

Productivity

• Solar energy is essential for ecosystem functioning
• Primary Production: Biomass/organic matter produced by plants
  • Measured in weight/energy per unit area/time
  • Gross Primary Productivity (GPP): Total production during photosynthesis
  • Net Primary Productivity (NPP): GPP minus respiration losses
  • Secondary Productivity: New organic matter by consumers
• Factors affecting productivity: Species, environment, nutrients, photosynthetic capacity

Decomposition

• Process of breaking down organic matter into inorganic substances
• Detritus: Dead plant/animal matter, raw material for decomposition
• Steps in Decomposition:
  • Fragmentation: Breaking down detritus into smaller particles
  • Leaching: Water-soluble nutrients leach into soil
  • Catabolism: Enzymatic degradation to simpler substances
  • Humification: Formation of resistant humus
  • Mineralisation: Release of inorganic nutrients
• Factors affecting decomposition: Chemical composition, climate

Energy Flow

• Sun is the main energy source
• Unidirectional flow of energy from producers to consumers to decomposers
• Trophic levels:
  • Producers (first level)
  • Primary Consumers (herbivores, second level)
  • Secondary Consumers (carnivores, third level)
• Energy decreases at successive trophic levels (10% law)
• Food chains and webs formed by dietary interdependencies

Ecological Pyramids

• Pyramids depict relationships in terms of number, biomass, energy
• Types of Pyramids:
  • Pyramid of Numbers
  • Pyramid of Biomass
  • Pyramid of Energy
• Characteristics:
  • Base: Producers
  • Apex: Top-level consumers
• Not all pyramids are upright (e.g., inverted pyramid of biomass in oceans)

Summary

• Ecosystems: Structural and functional units of nature
• Interaction between abiotic and biotic components
• Main components: Productivity, decomposition, energy flow, nutrient cycling
• Various cycles and processes sustain ecosystem functions
• Productive services like air and water purification

Exercises

• Fill in the blanks and questions about ecosystem components, productivity, decomposition, energy flow, and ecological pyramids.
• Encouragement to differentiate between similar concepts and describe various ecosystem functions.