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How can predators increase the number of species in a biological community?

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Zenaida macroura: mouring doves — ecology Mourning doves (*Zenaida macroura*) on their nest protected within the prickly branches of a cactus in the Sonoran Desert, Arizona, U.S.

Predators can increase the number of species in a biological community by acting as keystone species, which exert a disproportionately large influence on their environment relative to their abundance.12

They maintain local biodiversity primarily by controlling the populations of dominant species. In many communities, certain prey species are capable of outcompeting others for limited resources, potentially leading to a state where they dominate the landscape and exclude other species. By preying upon these dominant competitors, predators keep their numbers in check, which prevents them from monopolizing the environment and allows a wider variety of other species to establish themselves.12

A classic example is the predatory starfish Pisaster ochraceus. In rocky intertidal zones, this starfish feeds on mussels; when the starfish is removed, the mussel population expands rapidly and covers the shore so exclusively that other species are unable to survive there. Thus, the presence of the predator is essential for supporting the overall species diversity of the community.1