Short answers, pulled from the story.
An ecological threshold marks the specific moment when a small disturbance in external conditions triggers a rapid change within an ecosystem. This system responds with non-linearity to pressures from human activities or natural processes rather than gradual linear responses.
The ecosystem crosses its threshold when it passes a point of no return where recovery becomes extremely unlikely through inherent resilience alone. Ecological extinction serves as a definitive example of such irreversible loss that occurs after this crossing.
Scientists identify thresholds by processing time series data thought to display a significant shift and looking for possible jumps within historical information. Time series analysis remains a primary tool for locating abrupt changes in ecosystem states using methods to enhance and localize detected jumps.
Documented examples exist in the thresholds database maintained by Resilience Alliance which includes over one hundred cases. The Santa Fe Institute also contributes to this collection of recorded instances showing clear lakes turning into turbid ones.
Sudden shifts in ecosystem states induce changes in human understanding of management needs and alter institutions responsible for carrying out work. These feedback loops between nature and governance create complex adaptive patterns over decades that reshape societal responses.