Overview
This lecture explains trophic levels in food chains, covering the roles of producers, consumers, energy transfer, apex predators, omnivores, and decomposers.
Trophic Levels in Food Chains
- Trophic levels are different positions in a food chain.
- The first trophic level is always a producer, such as plants or algae.
- Producers make their own food using photosynthesis and sunlight energy.
- Primary consumers (trophic level 2) eat producers and are called herbivores.
- Secondary consumers (trophic level 3) eat primary consumers and are carnivores.
- Tertiary consumers (trophic level 4) eat secondary consumers and are also carnivores.
- Most food chains have no more than four or five trophic levels.
Energy Transfer in Food Chains
- Only about 10% of the energy at each trophic level is passed to the next level.
- Energy decreases at each level (e.g., 1,000 joules → 100 joules → 10 joules → 1 joule per level).
Special Roles in Food Chains
- Apex predators are at the top trophic level and have no natural predators.
- Omnivores, like bears, eat both producers and consumers and usually fit into trophic level 3, though imperfectly.
Decomposers and Detritivores
- Decomposers (bacteria, fungi) break down dead matter, recycling nutrients to the soil.
- Detritivores (some worms, small animals) also help decompose and recycle nutrients for producers.
Key Terms & Definitions
- Trophic level — a step or position in a food chain
- Producer — organism that makes its own food (usually by photosynthesis)
- Primary consumer — herbivore that eats producers
- Secondary consumer — carnivore that eats primary consumers
- Tertiary consumer — carnivore that eats secondary consumers
- Apex predator — predator at the top of a food chain, with no predators itself
- Omnivore — organism that eats both plants and animals
- Decomposer — organism that breaks down dead material and recycles nutrients
- Detritivore — animal that feeds on dead organic material
Action Items / Next Steps
- Review examples of food chains and identify the trophic levels of each organism.
- Practice calculating the energy transfer between trophic levels.