Ecological threshold

An ecological threshold is a boundary in environmental conditions or pressures beyond which a small additional change can trigger a large or persistent change in an ecosystem.

Alternative stable states: Distinct ecosystem configurations that can persist under similar environmental conditions. Feedbacks can stabilize different ecosystem states on opposite sides of a threshold.
Ecosystem: A community of organisms interacting with one another and with their physical environment. Thresholds describe changes in ecosystems, not only in individual populations.
Planetary boundaries: A framework identifying Earth-system processes and proposed limits for maintaining a stable, habitable planet. It applies threshold reasoning to risks spanning the global Earth system.
Clear-water–turbid-water regime shift: A lake transition between a clear, plant-rich state and a turbid state dominated by algae. Nutrient enrichment can push shallow lakes across a threshold between these states.
Ecological tipping point: A critical point at which a small perturbation can trigger an abrupt, self-reinforcing ecosystem shift. It describes the abrupt transition that can occur when a threshold is crossed.
Ecological resilience: The capacity of an ecosystem to absorb disturbance while retaining its structure and functions. Resilience determines how much pressure an ecosystem can absorb before changing state.
Early warning signal: A measurable change that may indicate an approaching shift in a system's behavior. Monitoring these signals can help detect rising risk before a threshold is crossed.
Coral bleaching: The loss of symbiotic algae from corals, often caused by heat stress. Severe or repeated heat stress can push coral reefs toward persistent decline.
Hysteresis: A system property in which its response depends on its history, so reversing a pressure may not reverse the change. It explains why returning conditions below a threshold may not restore the former ecosystem.
Ecological state variable: A measurable quantity used to describe an ecosystem's condition, such as vegetation cover or nutrient concentration. State variables make threshold-related ecosystem changes measurable.

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