A series of changes in population sizes across trophic levels due to top predators regulating intermediate species; trophic cascades may appear when a top predator is removed.

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Trophic cascades describe how top predators influence multiple levels of a food web through top-down control. When a top predator is present, it suppresses intermediate consumers and herbivores, reducing pressure on lower trophic levels and vegetation, which helps maintain ecosystem structure. If the top predator is removed, these controls disappear, causing downstream changes across several levels—prey populations shift, herbivory changes, and vegetation or habitat structure can respond in a cascade of effects. Examples like wolves limiting elk and allowing vegetation to recover, or sea otters keeping sea urchin numbers in check so kelp forests persist, illustrate this chain of indirect effects.

The other terms refer to different ideas: primary succession is about new communities forming after disturbance; biomass is a measure of the amount of living matter; a phase shift is a rapid, overall change in the ecosystem's state, not specifically the sequential, predator-driven changes across trophic levels.