A food web is the structure of a biome and the basis for retrospective in procedural evolution. Food webs are set up by trophic level, having many different niches in each level. Lines between niches show consumption. The number of niches in each level decreases as you go up the levels, and the overall number of niches is determined by the biodiversity or succession stage.
Each biome will require its own food web. The structure of a food web is up to its creator, but extremely important because it will have extreme in-game consequences. Any visual food web must be accompanied by definitions for all of its niches.