Trophic Levels in Ecosystems (College Board AP® Environmental Science): Study Guide

Energy is required to maintain ecosystems:

• All ecosystems depend on a continuous input of high-quality energy, primarily from the Sun

  • This is essential for maintaining the structure and function of ecosystems

• Energy flows through the ecosystem, allowing organisms to carry out life processes

Energy flows, matter cycles:

• Energy flows in one direction—from the Sun to producers and then through consumers

• Matter, such as carbon, nitrogen, and water, cycles between organisms and the environment

Matter is conserved

• Matter is not created or destroyed

• It is continuously cycled through biogeochemical cycles

Key biogeochemical cycles:

• Carbon cycle:

  • Carbon moves between the atmosphere, organisms, and fossil fuels

• Nitrogen cycle:

  • Nitrogen is cycled through the atmosphere, soil, and organisms

• Phosphorus cycle:

  • Phosphorus moves through rocks, soil, water, and organisms

Ecosystems rely on these cycles:

• Balanced biogeochemical cycles support healthy ecosystems

  • This is because they help to maintain the availability of essential nutrients

Trophic levels are the steps in a food chain or food web

• They represent how energy flows through an ecosystem

In terrestrial and near-surface marine communities:

• Energy flows from the Sun to producers in the lowest trophic levels and then upward to higher trophic levels

Tropic levels:

1. Producers (e.g., plants, algae)

2. Primary consumers (herbivores)

3. Secondary consumers (carnivores/omnivores)

4. Tertiary consumers (top predators)

Producers capture solar energy:

• Producers (e.g., plants, algae, phytoplankton) convert solar energy into chemical energy through photosynthesis

• Example: A prairie ecosystem where grass (producers) captures sunlight to grow

Consumers transfer energy:

• Primary consumers (herbivores) eat producers

• Secondary and tertiary consumers eat other consumers, transferring energy upward in the food chain

• Example: Earthworms decompose organic matter in forests, enriching the soil

Decomposers recycle matter:

• Decomposers like fungi and bacteria break down dead organisms, returning nutrients to the soil or water

• Example: Earthworms decompose organic matter in forests, enriching the soil