Ecosystem Structure Module
# Ecosystem Structure Module: Energy, Trophism, and Productivity
Energy Inputs and Outputs
Introduction
Energy inputs and outputs are critical to understanding ecosystem functionality.
Energy Inputs
All energy inputs come from the sun.
Energy Outputs
Energy outputs radiate from the Earth back into space.
Nutrient Cycles
Nutrients are cycled within the Earth system, making nutrient flow a closed system.
Open vs. Closed Systems
The flow of energy is an open system as there is a constant influx of solar energy.
Nutrient cycling represents a closed system because nutrients remain within the ecosystem.
Example:
Nitrogen Cycle as a closed system.
Atmospheric nitrogen is fixed by bacteria, taken up by plants, consumed by animals, decomposed back into the atmosphere.
First Law of Thermodynamics
States that energy cannot be created or destroyed, only transformed.
Examples of Energy Transformation:
Chemical energy (food such as ice cream) transformed into kinetic energy (movement).
Light energy transformed into chemical energy (via photosynthesis).
Photosynthesis and Phytoplankton
Photosynthesis Overview
Converts heat and light energy into chemical energy (glucose).
Most photosynthesis occurs in marine ecosystems; phytoplankton are key autotrophs.
Chemical Reaction:
Water + Light Energy → Glucose + Oxygen
Ecosystem Energy Flow
Energy Flow through Ecosystem
Energy enters via sunlight and is harnessed via photosynthesis by producers.
Energy transitions through consumers (herbivores → carnivores) and decomposers.
Illustration of Energy Flow
Red arrows denote energy flow, and green arrows represent nutrient cycling.
Energy is lost as heat when transitioning between trophic levels; it is transformed but not truly lost.
Trophic Structure
Key Terms
Producers: Organisms that produce their own food (e.g., plants, phytoplankton).
Primary Consumers: Herbivores that consume producers.
Secondary Consumers: Carnivores or omnivores that consume primary consumers.
Decomposers: Organisms like bacteria and fungi that break down dead organic material.
Autotrophs vs. Heterotrophs
Autotrophs (producers): Organisms that generate their own energy.
Heterotrophs (consumers): Organisms that obtain energy by consuming others.
Types of Consumers
Herbivores: E.g., geese, iguanas, pandas.
Carnivores: E.g., foxes, sharks, otters.
Omnivores: E.g., raccoons, dogs, bears.
Detritivores: Feed on dead organic material; examples include worms, insects.
Decomposers: Dismantle dead organic matter, e.g., bacteria, fungi.
Energy Transfer in Trophic Levels
Basic Structure of Trophic Levels
Diagram of energy pyramid demonstrates how energy flows from producers to tertiary consumers.
Producers form the base; energy diminishes with each successive consumer level.
Food Chains and Webs
Food Chain: Simple linear model showing successive consumption among organisms.
Food Web: Complex interconnections of various food chains in an ecosystem, showing much richer relationships and energy transfers.
Keystone Species: A term to explore in future lectures as pivotal figures in maintaining ecosystem structure.
Ecosystem Productivity
Definition of Productivity
Productivity measures the rate of energy accumulation in organisms (e.g., biomass).
Gross Primary Productivity (GPP)
Defined as the total energy captured by producers from sunlight. ~1% of sunlight energy captured by plants.
Net Primary Productivity (NPP)
NPP = GPP - Energy used for respiration. Typically lower than GPP due to energy use by organisms for metabolism.
Significance of Productivity
Indicates the health and sustainability of ecosystems.
Variation by Biome
Productivity is often highest in tropical rainforests and coral reefs and lowest in deserts and open oceans.
Seasonal Productivity
Productivity changes seasonally, with variation in sunlight impacting biomass and energy accumulation.
Example: Visual growth cycles from 2000 to 2010 illustrating seasonal differences.
Energy Transfer Efficiency
Energy Transfer: Average 10% energy transfer efficiency between trophic levels.
Mathematical Model:
Energy Flow:
Producers = 100% energy (less than 1% of light energy)
Primary Consumers = 10%
Secondary Consumers = 1%
Tertiary Consumers = 0.1%
Real World Case Study: Energy Efficiency in Silver Springs, Florida
Producers: 21,000 kcal/m²/year
Primary Consumers: ~3,368 kcal
Efficiency Calculation: Percentage of energy transferred calculated by dividing energy at each level by energy at the previous level.
Biomass Pyramid
Biomass Definition: Weight of living material (grams/m²).
Biomass pyramids may differ for terrestrial and aquatic environments:
Terrestrial: Upright pyramids due to ample tree biomass.
Aquatic: Inverted pyramids; high energy yield from phytoplankton, but low biomass weight relative to higher trophic levels (e.g., fish, marine mammals).
Conclusion
Summary of producers, consumers, decomposers, productivity, energy flow, and trophic levels, including ecological efficiency and the distinction between energy pyramids and biomass pyramids.
Note on Chemosynthesis: Some bacteria use chemical processes for energy production similar to photosynthesis but without sunlight.
Achieving Clarity in Complex Systems
Utilize food chains, webs, efficiency data, and varying productivity rates to paint a comprehensive picture of ecosystem functioning.
Study Tips: Focus not only on definitions but also on relationships between terms (e.g., how GPP and NPP relate to trophic levels).