Trophic Levels

Trophic Levels (troph - feeding) generally describe how an organism gets its food. The term, "food" describes molecules that can be broken down through cellular respiration to provide energy.

Autotrophs (auto - self) are any organisms that can make its own food inside of its cells
Heterotrophs (hetero - other) have to get their food from other sources besides their own cells

Autotrophs

Autotrophs (also called, "producers") can make their own food, but they need an energy source, and carbon molecules that can be joined together to store the energy in their bonds.

Photosynthesis captures the energy from the sun, and stores it in glucose molecules made from carbon dioxide and water.
- Examples include plants, algae, phytoplankton, or cyanobacteria
Chemosynthesis also makes glucose, but it captures energy from heat and inorganic molecules.
- Chemosynthetic organisms are rare, but bacteria living near deep-sea vents are the common example organism.

Heterotrophs

Heterotrophs (also called, "consumers") need to bring in organic molecules that store energy.

Consumers must have a way to break down food into simple molecules that can be used for respiration.
- Cells have lysosomes to digest (break down) large molecules
- Multicellular organisms have digestive systems that break down larger chunks of food into molecules that can be transported to individual cells.
- Some digestive systems can only break down specific types of food (plant or animal), while others are more general.
Within a food web, organisms with similar food needs are grouped in to trophic levels.
- Primary Consumer (Herbivore) - organisms that eat producers.
  - Terrestrial (on land) primary consumers eat grass, leaves, fruit, seeds or roots.
  - Aquatic (in water) primary consumers feed on aquatic plants, algae or phytoplankton.
  - Terrestrial Examples: Deer, Grasshoppers, Fruit Bats,
  - Aquatic Examples: Minnows that eat algae, Krill (small shrimp like animals that eat phytoplankton)
- Secondary Consumers - carnivores that eat herbivores
  - Terrestrial examples: wolf that eats deer; bird that eats grasshoppers
  - Aquatic examples: Bass that eat minnows, Humpback whales that eat krill
- Tertiary Consumers - carnivores that eat carnivores
  - Terrestrial examples: Tree snakes that eat birds that eat insects; Hawks that eat tree snakes (hawks would not be in a higher level; they are still carnivores that eat carnivores)
  - Aquatic Examples: turtles that eat bass, Killer Whales that eat young humpback whales
- Scavengers - organisms that roam in search of dead organisms
  - Terrestrial Examples: vultures, hyenas
  - Aquatic Examples: crabs, beetles
- Decomposers - organisms that grow on and break down dead organisms
  - Terrestrial Examples: fungi (mushrooms), bacteria, insect larvae
  - Aquatic Examples: fungi (water mold), bacteria
Omnivores - (Omni - all; vore - eater) organisms that eat producers and consumers
- They must have digestive systems that are able to break down plant material and animal tissue - most organisms specialize in one or the other
- The term is not usually used as a trophic level
- Examples: many songbirds eat seeds, berries, insects and worms; grizzly bears eat berries and fish