Review the place of producers, consumers, and decomposers in the ecosystem. Relate how the energy flow goes from sun-producer-consumer-decomposer. Define trophic level and stress that at each level, less and less of the energy originally captured by producers becomes available. There is an energy loss at each trophic level. Show a pyramid of biomass, discuss the biomass difference at each level and relate that to the energy difference.
Invert the pyramid to show how unstable it can become.Discuss and question the effect that changing the biomass in one level has on the biomass (creatures) in a second level. Stress that the changes in population decrease in one level will lead to population decreases in all levels, with harmful results.