Individual and Community

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-Tertiary extinction event which was an ecological collapse widely believed to be caused by an impact event.

source: http://en.wikipedia.org/wiki/Ecological_collapse