• Organisms can be classified into trophic (feeding) levels depending on how they get their energy.
  • Organisms that get their energy from nonliving sources (sun, organic matter) are called autotrophs (producers) and make up the 1st trophic level.
  • Organisms that get their energy from other living things are called heterotrophs (consumers).
  • Heterotrophs that eat autotrophs make up the 2nd trophic level and are called primary consumers.
  • The third trophic level consists of secondary consumers and eat primary consumers.
  • Ecosystems are normally limited to about 5 trophic levels.
  • All energy in an ecosystem is derived from the sun*.
  • This energy is converted to sugar (chemical energy) by plants through the process of photosynthesis.
  • A food chain shows the transfer of energy from one trophic level to another.
  • Whenever energy is transferred, some get lost.

Energy Pyramids

  • Since energy is lost each time it is transferred, each trophic level receives less energy than the level before it.
  • Also, energy gets used at each level, so only 10% of the energy from one trophic level gets passed onto the next trophic level.
  • This can be shown using an energy pyramid.
  • The size of the boxes represents the amount of energy in each trophic level.

Ecological Niches

  • The function a species serves in its ecosystem, including what it eats, what eats it, and how it behaves.
  • No two species occupy identical niches.

Types of Consumers

  • A sequence of organisms, each feeding on the next, showing how energy is transferred from one organism to another.
  • pine cone -> red squirrel -> weasel -> goshawk
  • Energy is continuously lost from all levels of the food chain.
  • Food chains do not exist in nature.
  • Create a sample food chain using the following organisms: grass, snakes, snails, birds.
  • What happens when one link is broken in a food chain?

Trophic Level

  • The level of an organism in an ecosystem depends on its feeding position along a food chain.
  • First trophic level – producers
  • Second trophic level – primary consumers
  • Third trophic level – secondary consumers
  • Fourth trophic level – tertiary consumers

Ecological Pyramids

  • A representation of energy, numbers, or biomass (the mass of living organisms in a given area) relationships in ecosystems.
  • Energy pyramid – Energy loss and transfer between trophic levels; the size of each layer represents the amount of energy available at that trophic level.
  • Only about 10% of the energy taken in by the individuals at one trophic level is passed on to individuals at the next level.
  • 10% of it is used to build new biomass (the rest going to metabolic processes). In a pyramid of productivity, each step will be 10% the size of the previous step (100, 10, 1, 0.1, 0.01)

Energy Pyramid

  • Pyramid of Energy Flow
  • 10% passed on to next level (a lot energy is lost as HEAT or to fuel prey’s bodily functions)
  • At each trophic level, the bulk of the energy received from the previous level is used in metabolism
  • This energy is released as heat energy and lost to the ecosystem
  • Eventually, all energy is released as heat

Numbers and Biomass Pyramids

  • In a forest ecosystem, the tiny plant-feeding insects in the second trophic level outnumber the trees in the first trophic level.
  • However, the biomass of all the trees is much greater than the biomass of herbivores.
  • Example Biomass Pyramid
author avatar
William Anderson (Schoolworkhelper Editorial Team)
William completed his Bachelor of Science and Master of Arts in 2013. He current serves as a lecturer, tutor and freelance writer. In his spare time, he enjoys reading, walking his dog and parasailing. Article last reviewed: 2022 | St. Rosemary Institution © 2010-2024 | Creative Commons 4.0


  1. 10% of it is used to build new biomass (the rest going to metabolic processes). In a pyramid of productivity each step will be 10% the size of the previous step (100, 10, 1, 0.1, 0.01)

  2. I love this page even if it only displays few informations, one can still learn a lot from it… but what realy is Kcal???

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