Catastrophes

Catastrophes are in one sense, merely an extreme form of environmental stochasticity. It is, however, useful to distinguish them for several reasons:

1. Often distinguished as events happening at random intervals in which a large proportion of the individuals in the population die.

2. Even though catastrophic declines may occur very rarely, they have a large impact on whether populations are able to persist.

3. Catastrophes occur infrequently, and we're not likely to see one or to see how large its effect is while we're watching. Even a relatively long time-series may not include them. Nonetheless, if catastrophes are big enough, meaning that they eliminate a large enough fraction of the population, they may be the greatest threats to a population's persistence, even if they occur only once every 50 or 100 years.