fv8 - primary productivity

AP Environmental Science: Unit 1 – The Living World: Ecosystems

Topic: 1.8 Primary Productivity

Overview of Primary Productivity

  • Definition: The amount of energy in an ecosystem determines its capacity to support various species.

  • Gross Primary Productivity (GPP):

    • Represents the total energy captured by producers through photosynthesis.

    • Comparable to a business's total revenue, not accounting for expenses.

Energy Loss in Ecosystems

  • Energy Loss:

    • Some energy is lost during the process of photosynthesis.

    • This loss occurs through respiration, where energy is released into the atmosphere.

  • Net Primary Productivity (NPP):

    • Calculated by subtracting the energy lost to respiration from GPP.

    • Represents the energy available for growth and reproduction of producers.

    • Analogous to profit in a business, as it accounts for maintenance costs.

Productivity and Ecosystem Characteristics

  • Ecosystem Productivity:

    • Ecosystems are generally unproductive; 99% of sunlight is either reflected or not absorbed.

    • Only 1% of sunlight contributes to GPP, and 60% of GPP is lost to respiration.

    • Thus, only 40% of GPP (or 0.4% of total solar energy) is available for supporting growth.

  • Species Richness:

    • Higher productivity levels correlate with greater species diversity and the ability to support more consumers across trophic levels.

Key Terms to Review

  • Gross Primary Productivity (GPP): Total energy captured by plants through photosynthesis.

  • Net Primary Productivity (NPP): Energy remaining after plants use some for respiration.

  • Photosynthesis: Process by which plants convert sunlight, CO2, and water into glucose and oxygen.

  • Respiration: Process of releasing stored energy from organic compounds for life functions.

  • Species Diversity: Variety of different species in an ecosystem, including their abundance.

  • Trophic Levels: Different levels in a food chain where organisms obtain energy, from producers to top predators.

Financial Analogy of NPP

  • NPP as Profit:

    • NPP is akin to a business's gross revenue, representing total energy produced.

    • It reflects energy available for growth after accounting for maintenance costs, similar to profit after expenses.

    • NPP also measures energy loss, comparable to asset depreciation in business.

    • Efficiency of energy transfer between trophic levels is analogous to a business's return on investment