Lecture on Trophic Levels and Energy Flow in Ecosystems

Introduction to Trophic Levels

• Trophic levels represent the flow of energy in an ecosystem.
• Producers (typically plants) start most trophic levels.
• Followed by consumers (primary, secondary, tertiary, quaternary, etc.).

Question for Consideration

• Why are upper-level consumers (tertiary and above) often endangered?
  • 2015 study: 77% of top predators were critically endangered.

Energy Flow in Food Webs

• Food web: a representation of energy flow, with arrows indicating direction from eaten to consumer.
• Energy starts from the sun and ends as heat in the atmosphere.

Case Study: North Atlantic Food Web

• Complex with many species.
• Cod is a crucial species; heavily overfished.

Source and Transformation of Energy

• Sun is the ultimate energy source for most ecosystems (except hydrothermal vents).
• Photosynthesis: Conversion of sunlight into food energy by producers.

Laws of Thermodynamics and Biological Systems

• First Law: Energy cannot be created or destroyed.
• Second Law: Energy transformations are inefficient; some energy is lost as heat.

Photosynthesis

• Process converting CO2 and water into glucose using sunlight.
• Glucose: foundation of food, used to build ATP.
• Byproduct: Oxygen gas released during water molecule splitting.

Cellular Respiration

• Conversion of food to ATP (energy form for cellular reactions).
• Requires oxygen, occurs in all living organisms including plants.

Energy Transfer Between Trophic Levels

• Inefficiency: Not all energy in a trophic level is transferred to the next.
• 10% Rule: Only 10% of energy is transferred to the next level.
  • Due to energy being used for metabolism, not all biomass being consumed, and heat loss.

Primary Productivity

• Measures the rate of carbon fixation (photosynthesis) in an ecosystem.
• Factors affecting productivity:
  • Amount of light
  • Water availability
  • Biomass density
  • Nutrient availability (nitrogen, phosphorus, sulfur)

Ecosystem Examples

• Savannahs: High productivity due to sufficient light, water, plant density, and nutrients.
• Deserts: Low productivity due to water scarcity and low plant biomass.

Conservation of Top Predators

• Often endangered due to human impacts and lack of producers/habitat.
• Energy availability starts with producer biomass; crucial for supporting higher trophic levels.
• Conservation efforts should focus on saving producers for energy influx.