What term describes a fundamental change in the overall character of a community?

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Phase shift describes a change in the overall character of a community, meaning the ecosystem moves from one stable regime to another with a different dominant set of species, structure, and functioning. This happens when stress or disturbances push the system past a tipping point, and feedbacks then keep it in the new state even if the original pressure is reduced. Examples include coral reefs becoming algae-dominated after bleaching and overfishing, or a lake shifting from a clear-water state to a turbid, algae-dominated state. Biomass is simply the total mass of living matter in an area and doesn’t by itself denote a change in the community’s identity. A trophic cascade describes a sequence of effects through food levels, not a wholesale shift in the community’s character. A keystone species is about a single species with a disproportionately large influence, not a regime change.