They may be biotic or abiotic. Disturbance is any event that disrupts an ecosystem. A disturbance event may be internal or external. Furthermore, disturbances may act singly on individuals, populations, communities, and ecosystems or combinations thereof, or the total system at once. Disturbance may remove organisms, change resource availability, open gaps for colonization, or change ecosystem structure.
Disturbance is often a random, or stochastic, event.
It may also be seasonal, such as monsoon cycles. Time scales are important. An event that happens only once every 1000 or 10000 or 100000 or 1000000 years is much harder for species to adapt to than an event that happens once a week, or once a season, or once a year. In addition to temporal characteristics of disturbance, spatial characteristics are also important. On the other hand, it would take a very major and rare event to disrupt the entire North American continent, e.g., major tectonic shift or extra-terrestrial object impact .