A food web is a diagram of who eats whom in a community. Food webs were first described for relatively simple communities, such as those in tundras. Even in those communities, food webs are complex. Food webs in complex communities are incredibly complex.
Many animals feed from multiple trophic levels and on a large number of species.
One attempt to both simplify food webs and to clarify interactions is to distinguish between strong and weak interactions , i.e., to determine the extent to which eater and eaten affect one another. Keystone species Keystone species are species whose community influence is disproportionately large compared to their biomass. The term was coined by Paine and an outgrowth of his research on intertidal communities. Paine had noticed that, as the proportion of species in a marine zooplankton community increased, the proportion that are predators also increased. He decided to see if this relationship held in marine invertebrate communities.