Ecological collapse refers to a situation where an ecosystem suffers a drastic, if not permanent, reduction in carrying capacity for all organisms, often resulting in mass extinction. Usually, an ecological collapse can be precipitated by a disastrous event occurring on a small time scale, such as the Cretaceous–Paleogene extinction event which was an ecological collapse widely believed to be caused by an asteroid impact event.
Ecosystems have the ability to rebound from a disruptive agent. The difference between collapse or a gentle rebound is determined by two factors—the toxicity of the introduced element and the resiliency of the original ecosystem.
Through natural selection the planet's species have continuously adapted to change through variation in their biological composition and distribution. Mathematically it can be demonstrated that greater numbers of different biological factors tend to dampen fluctuations in each of the individual factors.