The prey should exhibit mild oscillations, and the predator should fluctuate little. This would stabilize prey abundances. However, if one prey species is abundant and the predator is unable to reduce its numbers, the result might be the maintenance of a continuously high predator density. Such an abundant predator might then eliminate a second prey species. This is a destabilizing effect of an alternative prey.
Predation can have far-reaching effects on biological communities.
A starfish is the top predator upon a community of invertebrates inhabiting tidally inundated rock faces in the Pacific Northwest. The investigator removed the starfish by hand, which of course reduced the number of species to 11. Soon, an acorn barnacle and a mussel began to occupy virtually all available space, outcompeting other species. Species diversity dropped from more than 12 species to essentially 2. The starfish was a keystone predator , keeping the strongest competitors in check.