Unit 8: Energy Flow and Ecosystem Dynamics

1. Energy Flow in Ecosystems

• Energy transfer follows the 10% rule—only about 10% of energy is passed to the next trophic level, while the rest is lost as heat.

• Trophic levels:

  • Producers (Autotrophs) – Convert sunlight into chemical energy via photosynthesis (e.g., plants, algae).

  • Primary Consumers (Herbivores) – Eat producers (e.g., rabbits, deer).

  • Secondary Consumers (Carnivores/Omnivores) – Eat herbivores (e.g., snakes, foxes).

  • Tertiary Consumers (Apex Predators) – Eat secondary consumers (e.g., hawks, wolves).

2. Energy Pyramids

• Show the relative amount of energy at each trophic level.

• Types:

  • Energy pyramid – Displays energy flow (measured in kcal or joules).

  • Biomass pyramid – Shows the mass of organisms at each level.

  • Numbers pyramid – Shows the number of individuals at each level.

3. Invasive Species

• Definition: Non-native species that disrupt ecosystems by outcompeting native species.

• Examples:

  • Kudzu vine (USA) – Overgrows and smothers native plants.

  • Zebra mussels – Outcompete native aquatic species.

• Impact: Can cause biodiversity loss, habitat destruction, and economic damage.

4. Ecological Succession

• The gradual change in ecosystems over time.

• Two types:

  • Primary Succession – Starts from barren land with no soil (e.g., volcanic islands, glaciers retreating).

  • Secondary Succession – Occurs after a disturbance (e.g., fire, flood) but soil remains intact.

• Pioneer species: First organisms to colonize (e.g., lichens, mosses).

5. Limiting Factors in Ecosystems

• Factors that restrict population growth.

• Types:

  • Density-dependent factors – Affected by population size (e.g., competition, disease, predation).

  • Density-independent factors – Affect populations regardless of size (e.g., natural disasters, climate change).

Connections to Previous Units:

• Trophic levels relate to photosynthesis (Unit 7) since producers rely on sunlight to create energy.

• Invasive species can disrupt biodiversity (Unit 9) by altering population dynamics.

• Ecological succession is influenced by environmental cycles (Unit 6) such as carbon and nitrogen cycles.