In this model, an ecological pyramid is drawn as four horizontal bars stacked from bottom to top. Which trophic level is shown by the widest bar at the base?

Explanation

Ecological pyramids are drawn with the producers at the base, and each bar above holds the level that feeds on the bar below it. Decomposers fail because they are not one of the ascending trophic bars in this pyramid; they act across every level instead of occupying the base. Secondary consumers fail because they sit two levels above the base rather than at it.