FIGURE 20.10 Keystone predators. Sea stars are keystone predators in their rocky intertidal communities in Washington State. When sea stars are present, they consume mussels, which are strong competitors for space. This predation creates open spaces that inferior competitors can colonize. As a result, the diversity of species is high. In the absence of sea stars, the mussels dominate the surfaces of the intertidal rocks, and the diversity of species declines dramatically.
(Data from T. T. Paine, “Intertidal community structure: Experimental studies on the relationship between a dominant competitor and its principal predator,” Oecologia 15 (1974): 93–