Food webs describe the relationships — links or connections — among species in an ecosystem, but the relationships vary in their importance to energy flow and dynamics of species populations. Some trophic relationships are more important than others in dictating how energy flows through ecosystems. Some connections are more influential on species population change. Based on different ways in which species influence one another, Robert Paine proposed three types of food webs based on the species of a rocky intertidal zone on the coast of Washington (Ricklefs 2008, Figure 2). Connectedness webs (or topological food webs) emphasize feeding relationships among species, portrayed as links in a food web (Paine 1980). Energy flow webs quantify energy flow from one species to another. Thickness of an arrow reflects the strength of the relationship. Functional webs (or interaction food webs) represent the importance of each species in maintaining the integrity of a community and reflect influence on the growth rate of other species' populations. As shown in Figure 2, limpets Acmaea pelta and A. mitra in the community consume considerable food energy (energy flow web), but removal of these consumers has no detectable influence on the abundance of their resources (functional web). The most effective control was exerted by sea urchin Stronglocentrotus and the chiton Katharina (Ricklefs 2008).
