Question

What is measured by 'Productivity' in an ecosystem?

• A. The rate of energy transfer between trophic levels
• B. The rate of biomass production by living beings
• C. The rate of nutrient absorption by plants
• D. The rate of decomposition of organic matter

Answer 1

Answer:

B. The rate of biomass production by living beings

Ecosystem Productivity: A Core Ecological Concept

What is Ecosystem Productivity?

• Productivity in an ecosystem refers to the rate at which biomass is produced by living organisms over a given period. It quantifies the energy captured and converted into organic matter within an ecosystem.
• It is a crucial measure of an ecosystem's health and its capacity to support life.

Types of Primary Productivity

• Primary Productivity: This is the rate at which producers (primarily plants and algae through photosynthesis) convert solar energy into organic compounds (biomass).
• Two main types of primary productivity are vital for competitive exams:
  1. Gross Primary Productivity (GPP):
     • GPP is the total amount of organic matter (biomass) produced by photosynthesis in an ecosystem.
     • It represents the total energy captured by producers.
  2. Net Primary Productivity (NPP):
     • NPP is the amount of organic matter remaining after producers have accounted for their own metabolic needs (respiration).
     • NPP = GPP - Respiration (R).
     • NPP represents the energy available for consumption by herbivores and other trophic levels, making it a critical measure of an ecosystem's energy flow and biomass accumulation.

Units of Measurement

• Productivity is typically measured in terms of:
  • Weight (biomass) per unit area per unit time: e.g., grams per square meter per year (g/m²/year) or metric tons per hectare per year (tonnes/ha/year).
  • Energy per unit area per unit time: e.g., kilocalories per square meter per year (kcal/m²/year).

Factors Influencing Primary Productivity

• Sunlight: The primary energy source for photosynthesis; its intensity and duration significantly impact productivity.
• Temperature: Optimal temperature ranges support higher metabolic rates and photosynthetic efficiency.
• Water Availability: Essential for photosynthesis and nutrient transport.
• Nutrients: Availability of essential nutrients like nitrogen, phosphorus, and potassium often limits productivity in various ecosystems.
• Carbon Dioxide (CO2): A key raw material for photosynthesis.

Secondary Productivity

• Secondary Productivity refers to the rate of biomass production by consumers (heterotrophs) through the assimilation of organic matter from other organisms.
• It represents the energy converted into consumer biomass.

Ecological Significance

• Productivity dictates the carrying capacity of an ecosystem and the amount of energy available to higher trophic levels.
• High productivity indicates a healthy and robust ecosystem capable of supporting diverse life forms.
• Understanding productivity is vital for ecosystem management, conservation efforts, and assessing the impact of human activities on natural environments.

Examples of Ecosystem Productivity (for competitive exams)

• Highest NPP Ecosystems:
  • Tropical Rainforests: Due to high rainfall, temperature, and sunlight.
  • Coral Reefs: Highly productive marine ecosystems despite nutrient-poor surrounding waters.
  • Estuaries: High nutrient input from both land and sea.
• Lowest NPP Ecosystems:
  • Deserts: Limited by water availability.
  • Open Oceans (especially deep oceans): Limited by light penetration and nutrient availability.
  • Tundra: Limited by low temperatures and short growing seasons.