Ecosystem

Notes on Chapter 12: Ecosystem

12.1 Ecosystem Structure and Function

An ecosystem is defined as the dynamic and complex interaction of living organisms (biotic components) and their environment (abiotic components). Ecosystems can vary in size and complexity, from small ponds to vast forests and oceans. Ecologists often categorize ecosystems into terrestrial (like forests, grasslands, and deserts) and aquatic (like lakes, rivers, and wetlands). Man-made ecosystems, such as crop fields and aquariums, also fall under this classification.

Components of Ecosystem

• Abiotic Components: These include non-living elements like sunlight, temperature, water, air, and minerals.
• Biotic Components: These encompass all living organisms within the ecosystem, categorized into:
  • Producers (autotrophs): Organisms that produce their own food, mainly through photosynthesis. This group primarily includes green plants and phytoplankton in aquatic ecosystems.
  • Consumers (heterotrophs): Organisms that depend on other organisms for food. They can be primary consumers (herbivores), secondary consumers (carnivores), and tertiary consumers.
  • Decomposers: Organisms such as fungi and bacteria that break down dead organic matter, recycling nutrients back into the ecosystem.

Energy Flow and Productivity

Energy flow through an ecosystem follows a one-way pathway:

1. Producers capture solar energy through photosynthesis.
2. Consumers obtain energy by consuming the producers or other consumers.
3. Energy is lost as heat at each trophic level, following the Second Law of Thermodynamics.

Productivity refers to the rate of biomass production, which can be categorized into Gross Primary Productivity (GPP) and Net Primary Productivity (NPP):

• GPP: The total energy captured by all producers in a given time period.
• NPP: Energy left after accounting for the energy used by producers in respiration (NPP = GPP - R).

12.2 Productivity

Primary productivity is crucial for ecosystem function, representing the total biomass produced by autotrophs. Influencing factors include:

• Plant species: Different species have varying photosynthetic efficiencies.
• Environmental factors: Availability of nutrients (nitrogen, phosphorus) and physical conditions (light, temperature).

The net primary productivity (NPP) is critical because it quantifies the energy available for consumption by primary consumers, and further, by secondary consumers.

12.3 Decomposition

Decomposition is essential for recycling nutrients within ecosystems. It involves breakdown of complex organic matter into simpler inorganic substances through several processes:

1. Fragmentation: Breakdown of detritus into smaller pieces by detritivores (e.g., earthworms).
2. Leaching: Loss of water-soluble nutrients from the detritus to the soil.
3. Catabolism: The process by which microbes break down detritus, ultimately releasing nutrients.

Stages of Decomposition

• Humification: Transformation of organic material into humus, a stable form of organic matter that retains nutrients.
• Mineralisation: The conversion of organic material to inorganic substances, making nutrients available for use by plants again.

12.4 Energy Flow

The flow of energy in ecosystems is unidirectional:

• Energy begins with solar input and is captured by producers.
• It then moves through various trophic levels (primary consumers, secondary consumers).

The 10% law highlights that only about 10% of energy is passed on to the next trophic level, with the remainder lost mainly as heat. Trophic levels are defined as:

• First level: Producers
• Second level: Primary consumers
• Third level: Secondary consumers

12.5 Ecological Pyramids

Ecological pyramids can illustrate relationships between different trophic levels in terms of:

• Numbers: The total number of organisms at each trophic level.
• Biomass: The total mass of living material at each level.
• Energy: The energy content available at each level.

Typically, pyramids of numbers and biomass are upright, indicating more producers than consumers. However, exceptions exist, such as the inverted pyramid of biomass in aquatic systems where larger biomass (fishes) exists at higher trophic levels compared to producers (phytoplankton). The energy pyramid remains upright since energy diminishes as it moves up the levels due to continuous loss as heat.

Overall, the pyramid structure emphasizes the efficiency of energy transfer and the overall balance of ecosystem productivity, structure, and function.

1. An ecosystem consists of interacting biotic and abiotic components.
2. Ecosystems can be classified into terrestrial and aquatic types.
3. Productivity (GPP and NPP) refers to the rate of biomass production.
4. Decomposition is crucial for recycling nutrients and involves fragmentation, leaching, and mineralisation.
5. Energy flow is unidirectional, starting from producers and moving up trophic levels.
6. The 10% law indicates that only 10% of energy is transferred to the next trophic level.
7. Ecological pyramids illustrate relationships between trophic levels in terms of numbers, biomass, and energy.
8. Primary productivity is influenced by plant species, environmental factors, and nutrient availability.
9. Decomposers play a significant role in breaking down organic matter and recycling nutrients.
10. Understanding ecosystems helps illustrate the complex interdependencies of life forms and their environments.