Food chain
These are the trophic levels of a food chain in Lake Ontario. Energy and nutrients flow from photosynthetic green algae at the bottom to the salmon at the top of the food chain. There are only four links in this chain because significant energy is lost between each successive trophic level.
Source
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"OpenStax College, Ecology of Ecosystems. October 17, 2013."
http://cnx.org/content/m44885/latest/Figure_46_01_03.jpg
OpenStax CNX
CC BY 3.0.
