Question

Consider this ecological pyramid found in the Great Lakes ecosystem. Ecological pyramids are diagrams that are used to show how much energy, the number of organisms, or how much biomass may be found at each trophic level of all the food webs of a community. Why are the autotrophs, in this case the algae, always placed at the base of the pyramid?

Answer 1

They are placed at the bottom because they are the lowest trophic level, and usually the energy flows upward in such diagrams. 

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Answer 2

they place at this point because they have the higher energy 
and their energy will dividing for the next one